Neural & Visceral Anatomy - Semester 2

Frontal
2x Parietal
2x Temporal
Occipital
Ethmoid
Sphenoid (skull bone that forms bridges between the skull and facial bones)

- 2 Maxillae which froms the upper jaw
- 2 Palatine bones
- 2 zygomatic bones otherwise known as ‘cheek bones’
- 2 Lacrimal bones
- 2 nasal bones providing the supportive bridge of the upper nose
- 2 inferior nasal concha
- 1 Vomer bone
- 1 Mandible which forms the lower jaw

The skullcap or calvaria consists of superior portions of the frontal, parietal and occipital bones. This is removed during a routine autopsy. At its most rostral/distal point in the saggital plane the suture is the vertex

The sutures of the skull are solid, fibrous joints (synarthroses), joining the bones of the skull together
Coronal Suture - between frontal and parietal bones
Saggital Suture - between left and right parietal bones
Squamous Suture - between temporal and parietal bones
Lambdoid Suture - between occipital and parietal bones

Bregma - Junction where coronal and saggital sutures meet. This anatomical landmark marks the anterior fontanelle (diamond-shaped soft spot) in infants which closes around 18 months

Lambda - Junction of the saggital and lambdoid sutures. This corresponds to the posterior fontanelle (traingular-shaped soft spot) in infants which closes within the first few months of life

Pterion - Region where the frontal, temporal, parietal and sphenoid (greater wing) bones meet, forming a 'H' shape. This is clinically signficant as it is the weakest part of the skull where the middle meningeal artery runs underneath it. Thus trauma to this area can cause an epidural hematoma, a life-threatening pooling of blood outside the blood vessel.

Asterion - Junction of the temporal, occipital and parietal bones. This area is used as a surgical landmark

a pyramid-shaped section of bone located at the base of the skull, between the sphenoid and occipital bones. It's a dense, hard portion of the temporal bone that houses the middle and inner ear structures and provides passageway for important nerves and blood vessels, such as the internal carotid artery, internal jugular vein, and facial nerve.

The most anterior and highest cranial fossa (scooped out area)
- Formed by the frontal bone, cribrifom plate of the ethmoid bone and the lesser wings / anterior body of the sphenoid bone
- Houses the frontal lobe of the brain and olfactory nerves which pass through the cribriform plate

The middle cranial fossa that is deeper than the anterior
- Formed by the greater wings and sella turcica (hypophyseal fossa) of the sphenoid bones and the petrous portion of the temporal bones
- Contains the temporal lobes and the pituitary gland which sits in the sella turcica (shallow depression)

The most posterior and deepest cranial fossa with the foramen magnum
- Formed by the occipital bone, petrous parts of the temporal bone and parietal bones
- Houses the cerebellum and brainstem with other important structures passing through eg: Spinal cord through foramen magnum

Anterior / Rostral = towards the front of the brain (or top of spinal cord)
Posterior / Caudal = towards the back of the brain (or bottom of spinal cord)
Superior / Dorsal = towards the top of the brain (or back of spinal cord)
Inferior / Ventral = towards the bottom of brain (or front of spinal cord)
Medial = towards midline of brain
Lateral = away from midline of brain

Sulci refers to the grooves or depressions seperating gyri (think 'sulci' meaning sulky or depressed).

Gyri refers to the ridges or folds on the surface of the cerebral cortex (think 'Gyri' meaning Gyros requiring folding)

Central sulcus - divides the frontal and parietal lobes
Lateral sulcus (Sylvia fissure) - divides the temporal lobe from the frontal and parietal lobes
Parieto-occipital sulcus - divides the parietal lobe from the occipital lobe
Calcarine sulcus - medial surface of occipital lobe, it contains the primary visual cortex

Precentral Gyrus - On the Frontal lobe before the central Sulcus
Postcentral Gyrus - On the Parietal Lobe after the central sulcus
Superior temporal Gyrus - On the Temporal lobe inferior to the lateral sulcus
Cingulate Gyrus - Viewed only mid-saggitally (brain cut in half) on the medial surface of each cerebral hemisphere. It is a component of the limbic system, a collection of brain structures involved in processing emotions, memory, and motivation.

- Controls higher cognitive processes such as decision making, problem solving and planning (prefrontal cortex), and gustatory cortex (perception of taste)
- Contains the primary motor cortex (voluntary movement) and areas responsible for speech production (Broca’s area)

- Processes sensory information like touch, temperature and pain
- Contains the primary somatosensory cortex, which maps sensations from different parts of the body

- Handles auditory processing, language comprehension, memory formation and olfactory stimuli
- Contains the primary auditory cortex and the hippocampus, essential for long-term memory

- Dedicated to visual processing, including the recognition of objects, shapes and colours
- Contains the primary visual cortex (calcarine sulcus)

Ventral means Inferior, therefore we are looking at the brainstem and cerebellum:

Pons - Bulging area of brainstem between midbrain and medulla, responsible for relaying signals
Medulla Oblongata - Inferior to Pons - controls autonomic functions like breathing and heart rate
Cerebellum - Posterior and inferior, involved in coordination, balance and fine tuning movements
Olfactory Bulbs - On the inferor surface of the frontal lobes - involved in smell

The meninges are three layers of protective membranes that surround the brain and spinal cord, collectively known as the central nervous system
- Meningitis is an inflammation of the meninges

From outermost to innermost:
1. Dura mater – Tough, fibrous outer layer.
2. Arachnoid mater – Thin, web-like middle layer.
3. Pia mater – Delicate inner layer that closely follows the brain's surface contours.

The dura mater is the outermost layer of the meninges and can be seperated into two layers:
Periosteal layer - attached to the inner surface of the skull
Meningeal layer - lies closer to the brain and forms dural reflections / sheets

The dura mater is are mostly fused but separate at certain points to form venous sinuses eg; superior sagittal sinus

Falx cerebri - between the cerebral hemispheres

Falx cerebelli - between the cerebellar hemispheres (cerebellum hemispheres)

Tentorium cerebelli - between the cerebrum and cerebellum

Diaphragma sellae - covers the pituitary gland in the sella turcica

A saddle-shaped depression located within the middle cranial fossa in the sphenoid bone at the base of the skull, housing the pituitary gland by forming a bone enclosure. The pituitary gland, also known as the hypophysis, sits within the sella turcica's deepest part, called the hypophyseal fossa.

The dura mater is highly vascular with the dura supplied by the middle meningeal artery which leaves through grooves in the skull. The middle meningeal artery runs from the maxillary artery, which is a branch of the external carotid artery and enters through the foramen spinosum.

The arachnoid mater lays just under the dura and is connected to the pia mater via the arachnoid trabeculae (spider web-like structure). The arachnoid mater does not follow the brains sulci, only bridging over them. Between the arachnoid and pia mater is the subarachnoid space, filled with cerebrospinal fluid (CSF), blood vessels and arachnoid trabeculae.

The arachnoid has enlarged subarachnoid spaces to accomodate increased CSF known as cisterns
1. Cisterna magna (cerebellomedullary cistern) – between the cerebellum and medulla
2. Pontine cistern – infront of the pons
3. Interpeduncular cistern – between the cerebral peduncles
4. Superior cistern (quadrigeminal cistern) – behind the midbrain, above the cerebellum

The pia mater is the innermost meningeal layer as it closely adheres to the brains surface. In particular, it follows all gyri and sulci of the brain. The pia mater is highly vascular, allowing blood vessels to pass into brain tissue.

The ventricular system is a network of interconnected, fluid-filled cavities within the brain called ventricles.

• Protection: Acts as a cushion, reducing the impact of trauma to the brain and spinal cord.
• Buoyancy: Reduces the effective weight of the brain, preventing pressure damage on the base of the brain.
• Chemical stability: Maintains a stable chemical environment by removing waste (catabolites) and delivering nutrients (Vitamins, growth factors and leptin).
• Immunological support: Helps protect against infection by acting as a barrier and clearing waste.

1. Lateral ventricles (1st and 2nd ventricles) – One sits in each hemisphere and is located deep within the frontal, parietal, temporal and occipital lobes
2. Third ventricle – narrow, midline structure located in the diencephalon (between the two halves of the thalamus)
3. Fourth ventricle – located dorsal (posterior) to the pons and medulla (of the brainstem) and ventral (anterior) to the cerebellum

CSF is produced by the choroid plexus, which is a network of capillaries and ependymal cells. It is found in the floor of the lateral ventricles and the roofs of the third and fourth ventricles. An estimated 500ml of CSF is produced daily but only about 150ml is present at any one time

A type of glial cell that lines the ventricles of the brain and the central canal of the spinal cord

Here is the pathway of CSF from production to resorption:
1. CSF is produced by the choroid plexus in the lateral ventricles
2. It flows through the interventricular foramen into the third ventricle where more CSF is added
3. CSF then flows through the cerebral aqueduct into the fourth ventricle where additional CSF is produced
4. From the fourth ventricle, CSF flows into the subarachnoid space via the median aperture or the lateral apertures.
5. CSF circulates around the brain and spinal cord in the subarachnoid space
6. CSF is reabsorbed into the venous system via the arachnoid villi / granulations which flow into the superior sagittal sinus (dural mater venous sinus).

The circle of Willis is a circular anastomosis of arteries located at the base of the brain, providing collateral bloodflow to the brain.

It is formed by the:
Basilar artery --> Posterior cerebral artery (PCA)
Posterior communicating artery - connects the internal carotids to PCA
Internal carotid arteries (ICA)
Anterior cerebral arteries (ACA)
Anterior communicating artery - connects the two ACA's

The brain supplied by two arterial systems; the internal carotid system anteriorly and the vertebrobasilar system posteriorly.

1. Internal carotid (left and right) arteries – arise from the common carotid arteries then enter the skull via the carotid canal. The internal carotid terminates at the Circle of Willis
2. These then emerge into the subarachnoid space, giving rise to middle cerebral artery (MCA), anterior cerebral artery (ACA), posterior communicating artery and the Ophthalmic artery (to the eye)

1. Vertebral arteries (left and right) arise from the subclavian arteries and ascend through the transverse foramina of cervical vertebral to enter the skull through the foramen magnum with the spinal cord
2. These merge at the base of the brain to form the basilar artery which travels along the posterior surface of the pons
3. The basilar artery gives off serveral branches then splits into two posterior cerebral arteries (PCA)

ACA supplies the medial, frontal and parietal lobes and then superior parts of the motor and sensory cortex

MCA supplies lateral surfaces of the frontal, parietal and temporal lobes

PCA provides the whole occipital lobe, inferior lateral temporal lobe and the thalamus and midbrain

The cerebral hemispheres of the brain are primarily supplied by internal carotid arteries (ACA & MCA) and the vertebral-basilar system (PCA)

The brainstem however is supplied mainly by branches of the vertebral arteries and the basilar artery, thus the brainstem relies more heavily on the vertebral-basilar system while the brain relies more on the internal carotid circulation.

Superior saggital sinus - runs along the top of the falx cerebri
Inferior saggital sinus - within the lower margin of falx cerebri
Straight sinus - formed by union of inferior saggital sinus and great cerebral vein
Confluence of sinuses - meeting point of the superio saggitla, straight and occipital sinuses
Transverse sinus - runs laterally from the confluence
Sigmoid sinus - Sinus continuing from the transverse sinus, draining into the internal jugular vein
Cavernous sinus - located on either side of the sella turcica

Grey matter contains neuron cell bodies, dendrites and synapses.
- It is found on the outer cortex of the brain and the inside of the spinal cord
- It is responsible for processing and cognition

White matter contains myelinated axons (nerve fibres)
- It is found deeper within the brain (beneath the grey matter) and on the outside of the spinal cord
- Responsible for communication between brain areas and spinal cord

• Corpus Callosum: Large C-shaped band of white matter that connects the two cerebral hemispheres, allowing communication between them.

• Internal Capsule: A V-shaped structure that contains ascending and descending nerve fibers (motor and sensory information) connecting the cerebral cortex with the brainstem and spinal cord. It passes between the thalamus and basal ganglia.

White fibre tracts are bundles of myelinated axons that act as communication pathways within the brain, connecting different regions and enabling information transfer.

o Association fibres – Connect areas within the same hemisphere (e.g., arcuate fasciculus).
o Commissural fibres – Connect corresponding areas in opposite hemispheres (e.g., corpus callosum connecting the two hemispheres).
o Projection fibres – Connect cortex with lower brain / spinal cord (e.g., internal capsule connecting the brainstem / spinal cord with the cerebral cortex).

Hemispheric lateralisation refers to the specialisation of function in each cerebral hemisphere. While both hemispheres are structurally similar, certain functions are more dominant in one:

• Left Hemisphere:
o Language (Broca’s and Wernicke’s areas)
o Logical reasoning
o Mathematics

• Right Hemisphere:
o Spatial and visual processing
o Creativity and imagination
o Emotional interpretation

The hypothalamus is a brain region located above the pituitary gland, acting as a control centre for hormone release. The pituitary gland is a pea-sized gland which sits at the base of the brain directly below the hypothalamus. They are interconnected by the pituitary stalk (infundibulum) and a network of blood vessels, enabling effective communication and regulation of hormone release. The hypothalamus controls
- Body temperature
- Blood circulation
- Regulation of food and water intake
- Sleep – wake cycle
- Sexual behaviour
- Stress responses

The hypothalamus sends signals (neurohormones) to the pituitary gland, telling it when to release its hormones. These signals are in the form of releasing hormones that travel through a network of blood vessels via the pituitary stalk/infundibular stalk. The pituitary gland produces and releases several hormones that affect other endocrine glands and the overall endocrine system. This interconnected relationship is known as the hypothalamic-pituitary axis.

The hypothalamus communicates with the anterior pituitary through a network of blood vessels called the hypophyseal portal system while its connected with the posterior pituitary via the pituitary stalk.

The anterior pituitary produces and secretes its own hormones whilst the posterior pituitary stores and releases hormones produced by the hypothalamus (does not synthesize its own hormones).

The Posterior Pituitary gland
- Produces two neurohormones: Oxytocin and Vasopressin (ADH)
- Oxytocin is responsible for stimulating lactation, uterine contraction during labour, social bonding and sexual reproduction
- Vasopressin is responsible for regulating blood volume and salt concentration

The Anterior Pituitary Gland
- Releases two types of hormones: Releasing factors (stimulate hormone release from anterior pituitary) and Inhibiting factors (inhibit hormone release from anterior pituitary)
LIST OF HORMONES
- Human growth hormone (Hgh): Stimulates the production of Inuslin growth factors (IGF's) for growth, protein synthesis etc
- Thyroid-stimulating hormone (TSH): stimulates synthesis and production of thyroid hormones
- Follicle stimulating hormone (FSH): Sperm production in males and oocytes (developing egg) in females
- Luteinizing hormone (LH): stimulates the secretion of estrogen, progesterone, causing ovulation. Supports the formation of the corpus luteum
- Prolactin: Promotes milk production
- Adrenocorticotropic hormone: Stimulates the secretion of glucocorticoids or steroids eg; cortisol
- Melanocyte-stimulating hormone: Unknown

Inputs to the Hypothalamus include:
- Limbic System (cortical to hypothalamus): Emotional regulation
- Retina (vision): Retinal ganglion cells (intrinsically photosensitive)
- Olfactory system: Pheromones for social behaviours
- Somatosensory system (Pain and sexual behaviour)

1) Stress response:
- During stress there is an increased activity of the medial prefrontal cortex (cingulate gyrus) this releases Corticotropin-releasing hormone (CRH) which is a peptide hormone which acts as a releasing hormone stimulating the anterior pituitary to release ACTH which in turn triggers the release of cortisol from the adrenal cortex. Moreover the ANS (sympathetic system) is activated

2) Control of cardiovascular function:
- Medial prefrontal cortex and amygdala again project to the hypothalamus which in turn innervates brainstem regions that regulate cardiovascular response. The brainstem modulates cardiovascular rates:
- In response to pain, respiratory distress or gastrointestinal issues
- For thermoregulation
- To maintain blood pressure during erect posture (upright)

Tonically active
- Decreased cardiac output
- Pupil Constriction
- Tears

Phasically Active
- Accommodation (process of sight focus)
- Tears (crying)
- Watery saliva production
- Pancreatic secretion
- Stomach motility (eating)
- Altered airway resistance (during activity v rest)
- Urination
- Sexual activity

The cranial parasympathetic division is responsible for functions such as secretion, vasodilation, pupillary constriction and accommodation. Parasympathetic fibers in the brainstem arise from four main cranial nuclei. These nuclei provide autonomic (visceral motor) output to glands, smooth muscle, and mucous membranes in the head, neck, thorax, and abdomen.

Edinger-Westphal Nucleus (Midbrain)
- CN III
- Controls pupil constriction via sphincter pupillae muscles and lens accommodation via the ciliary muscle

Superior Salivatory Nucleus (Pons)
- CN VII (facial nerve)
- Sends fibers to lacrimal glands for tear production and submandibular and sublingual glands for saliva production

Inferior salivatory Nucleus (Medulla)
- CN IX (glossopharyngeal nerve)
- Sends fibers to the otic ganglion (innervation of parotid gland) and the parotid salivary gland for salivation

Dorsal Vagus nucleus (Medulla)
- CN X (Vagus nerve)
- Sends preganglionic parasympathetic fibers to thoracic and abdominal viscera eg; hearts, lungs and GI tract
- This regulates heart rate, digestive secretions, bronchoconstriction

Tonically active (constant)
- Skin, muscle and gut vasoconstriction
- Inhibition of gut secretion and motility (immediate survival needs)
- Bladder inhibition

Phasically Active (sometimes)
- Sudomotor (sweating)
- Piloerection (goosebumps/hair standing on ends)
- Thick saliva production
- Increased cardiac output
- Pupil dilation
- Sexual activity

Paravertebral (sympathetic chain) ganglia (cervical, thoracic, lumbar, sacral and coccygeal ganglia)
- Runs bilaterally alongside the vertebral column (from the base of the skull to the coccyx), laying anterior to the transverse processes and lateral to the vertebral bodies


Prevertebral ganglia (Celiac, superior/inferior mesenteric ganglion superior hypogastric plexus)
- Lie anterior to the vertebral column and close to large abdominal arteries

Celiac Plexus
- Surrounds the celiac trunk just inferior to the diaphragm (T12-L1). It lies behind the stomach and anterior to the aorta
- Major autonomic plexus supplying the foregut organs (stomach, liver, pancreas, spleen)

Superior mesenteric ganglion
- Lies near the origin of the superior mesenteric artery, just below the celiac plexus
- Supplies midgut organs

Inferior Mesenteric ganglion
- L3 vertebral level near the origin of the inferior mesenteric artery, laing anterior to the aorta between the superior mesenteric and hypogastric plexus
- Supplies hindgut organs

Superior hypogastric plexus
- Lies anterior to L5 vertebral body just above the bifurcation of the aorta
- Carries sympathetic fibers to pelvic organs (urogenital system)

The enteric system coordinates peristalsis (the involuntary muscle contractions that move food through the digestive tract), secretion and local reflexes. The enteric nervous system is embedded in the walls of the gastrointestinal tracts, from the esophagus to the anus. It is often called the ‘second brain’ due to its semi-autonomous function as it is modulated by the sympathetic (inhibitory) and parasympathetic (excitatory) nervous systems but can act independently.

Myenteric plexus (beneath serosa membrane and between muscles)
- Located between the circular and longitudinal muscle layers of gastrointestines
- Controls gut motility eg; peristalsis (movement/motor action)

Submucosal Plexus (think parietal layer)
- Located in the submucosa layer of gastrointestines
- Controls secretions, blood flow and mucosal regulation

The basal ganglia is a cluster of nuclei found deep to the neocortex of the brain. The basal ganglia is continually monitoring what is going on in the cerebral cortex. Its motor effects are exerted through cerebral cortex. The basal ganglia has two pathways:

1. Promote Movement via direct pathway
2. Inhibit movement via indirect pathway

- C-shaped structure running alongside the lateral ventricle. Has a head (in the frontal body), a body and a tail (ending near the amygdala)
- Involved in motor control (eye movement - occulomotor loop), learning and reward systems

Putamen
- Lies lateral to the internal capsule forming the outer portion of the lentiform nucleus
- Involved in regulation of movement (limb and trunk)

The striatum is a deep-brain nucleus that links motivation to motor movements and is involved in the execution of simple motor tasks as well as more complex cognitive tasks, such as reward processing, decision-making, and social interactions. The striatum primarily includes: Caudate and Putamen

Globus pallidus (lateral and medial)
- Lies medial to the putamen forming the middle layer of the lentiform nucleus
- Lateral segment = indirect pathway of movement inhibition sending signals to subthalamic nucleus
- Medial segment = direct pathway of promoting movement

Subthalamic Nucleus
- Below the thalamus, found in the diencephalon.
- Crucial part of the indirect motor pathway for movement suppression/inhibition

Substantia Nigra
- Located anterior to the cerebral aqueduct, in the midbrain. Has two divisions: Pars compacta and Pars reticulata
- Pars compacta functions to produce dopamine for the basal ganglia circuit while pars reticulata is the major output nuclei for motor movement etc.

1) Cortical Input: Motor cortex, prefrontal cortex, cingulate cortex (limbic system), Frontal eyelids etc

2) Striatum: Putamen or caudate

3) Output: Globus Pallidus Internal segment or Substantia pars reticulata

4) Thalamus

5) Frontal cortex or the desired region for movement / action

1) Cortical Input

2) Striatum: Putamen or Caudate

3) Intrinsic Nuclei: Globus Pallidus External segment and Subthalamic Nucleus

5) Output: Globus Palldius Internal segment or substantia nigra pars reticulata

6) Thalamus

7: Output: Movement or action

1) Skeletomotor loop - controls facial, limb and trunk musculature, facilitating desired movement and inhibiting unwanted movements. Primary motor cortex --> Putamen

2) Occulomotor loop - controls eye movements (especially saccades). Frontal eye lids (prefrontal cortex) --> Caudate Nucleus

3) Prefrontal cortex loop – planning, decision making, and executive functions. Prefrontal cortex --> Caudate Nucleus

4) Limbic Loop – Involved in emotions, motivation and reward-related behaviour. Links emotion with movement eg; happy when smiling. Cingulate gyrus / Limbic system --> Ventral striatum

Parkinsons disease
- Loss of dopamine in substantia nigra (pars compacta) which means less direct pathway movements and more indirect pathway movement for movement inhibition
- Causes tremors, rigidity and bradykinesia (speed and amplitude of voluntary movement)

Huntington’s disease
- Degeneration of striatum (indirect pathways)

The cerebellum is the largest part of the hindbrain (rhombencephalon) and has two hemispheres joined by vermis. The cerebellum is responsible for posture and voluntary movement tuning and adjustments.

Anterior lobe – Above the primary fissure, important for limb/trunk movement

Posterior lobe – Largest lobe, important for fine motor coordination

Flocculonodular lobe – Smallest lobe, involved in balance and eye movements

Peduncles are bundles of white matter that connect the cerebellum to the brainstem. The three peduncles are:

Superior cerebellar Peduncle (SCP)
- Connects to midbrain with its main function being to send motor plans to the cortex and for the reception of spinal input
- Its main pathway is efferent (motor neurons) towards the motor cortex via the thalamus and afferents from the spinocerebellar

Middle Cerebellar Peduncle (MCP)
- Biggest peduncle connecting to the pons with its main function being the transmission of motor commands from the cortex to cerebellum
- Thus its main pathway is afferents (sensory neurons) from contralateral pontine nuclei (from cortex)

Inferior cerebellar peduncle (ICP)
- Connects to the medulla and carries mostly afferents from spinal cord and brainstem.
- Its main function is concerned with balance, proprioception and motor learning

Afferent (sensory neuron) projections arise from the:
- Cortex via pontine nuclei (MCP)
- Cortex via red nucleus and inferior olive (ICP)
- Spinal cord (ICP)
- Vestibular nuclei (ICP)

All efferent (motor neuron) projections arise from the:
- Deep cerebellar nuclei

Vestibulocerebellum (Flocculonodular lobe)
- For balance and eye movements
- Associated with vestibular nuclei (ICP)

Spinocerebellum (vermis and intermediate zones)
- For posture, muscle tone, trunk and limb coordination
- Associated with spinal cord input

Cerebrocerebellum / Neocerebellum (Lateral hemispheres)
- For planning, timing, precision of skilled movements
- Associated with motor and premotor cortex

There are four bilaterally paired deep nuclei that act as the primary output pathway for the cerebellum, processing information from the cerebellar cortex and sending signals to other brain areas, primarily to the brainstem and thalamus, from medial to lateral they include:
- Fastigial
- Globose (interposed nuclei)
- Emboliform (interposed nuclei)
- Dentate

Fat Guys Eat Donuts

Fastigial nucleus recieves its input from the vermis (spinocerebellum) and flocculonodular lobe (vestibulocerebellum). It sends this information to the vestibular nuclei and reticular formation for balance, posture and control of eye movements via vestibular system.

Interposed Nuclei recieve input from the intermediate zone of the spinocerebellum and send this to the red nucleus and to the motor cortex via the thalamus. They function for the coordination of limb movements, especially corrective action.

Dentate nucleus recieves its input from the lateral cerebeller hemispheres (cerebrocerebellum) and send its information to the contralateral motor and premotor cortex via the thalamus. Its function is planning, initiation and precision of voluntary movement.

The cerebellum is supplied by three paired arteries, branches of the vertebrobasilar system. From dorsal to ventral (high - low) these include the:

Superior Cerebellar artery (SCA) – From basilar artery supplying superior surface and dentate nucleus (most lateral nuclei)

Anterior Inferior Cerebellar Artery (AICA) – From basilar artery supplying anterior inferior surface and flocculus (small lobe for eye movement control & VOR)

Posterior Inferior cerebellar artery (PICA) – From the vertebral artery supplying posterior inferior surfaces, including the nodulus (a small node, especially on the vermis)

1. Midbrain (mesencephalon) – connects diencephalon to pons.
2. Pons – bulging middle section, connects cerebrum and cerebellum, bridge for tracts.
3. Medulla Oblongata – lowest part, continuous with spinal cord.

1) Origin or target of cranial nerves for sensory and motor function in head and neck
2) Ascending sensory tracts or descending motor tracts
3) Site that underlies critical functioning such as cardiovascular rate, respiratory rate and level of consciousness

• Anterior (rostral or ventral):
o Cerebral peduncles – large bundles of corticospinal & corticobulbar fibres; appear as two thick columns.
o Substantia Nigra - part of the basal ganglia and plays a crucial role in motor control and reward systems (Dopaminergic nucleus)
o Red Nuclei - plays a role in motor control and coordination. It's known for its high iron content, giving it a reddish appearance

• Posterior (caudal or dorsal): Four bubbles
o Superior colliculi – visual reflex centres.
o Inferior colliculi – auditory reflex centres.

• Anterior (ventral) surface:
o Pons – Large bulge due to transverse pontine fibres. Relays signals between cerebrum and cerebellum also contains cranial nerve nuclei

• Posterior (Dorsal) surface: (GO ABOVE TO VIEW THESE)
o 4th Ventricle – CSF-filled space between brainstem and cerebellum
o Cerebellar Peduncles – SCP = midbrain ↔ cerebellum, MCP = (pons ↔ cerebellum & ICP = medulla ↔ cerebellum

• Anterior surface:
o Pyramids – contain corticospinal tracts, visible along midline.
o Pyramidal Decussation - where the majority of motor fibres from the corticospinal tract cross over to the opposite side of the brainstem.
o Olives – oval swellings lateral to pyramids; contain olivary nuclei for motor learning.
o Inferior olivary Nucleus – Posterior to pyramids but anterior to ICP

• Posterior surface (dorsal):
o Floor of the 4th ventricle (upper medulla).
o Gracile Nucleus – medial to cuneate nucleus, processes sensory information from lower body including vibration, touch and proprioception
o Cuneate Nucleus and Tract – fine touch and proprioception for the upper body
o Vestibular Nuclei – near 4th ventricle, for balance and spatial orientation receiving its input from the inner ear
o Hypoglossal Nucleus – medial medulla near the midline at the floor of the 4th ventricle. For motor control of tongue muscles
o Medial Lemniscus – Runs centrally through medulla and pons providing an ascending sensory pathway (fine touch, vibration and proprioception)

Midbrain
• Posterior cerebral artery (PCA)
• Superior cerebellar artery (SCA)
• Basilar artery (small branches)

Pons
• Basilar artery (paramedian & circumferential branches)
• Anterior inferior cerebellar artery (AICA)
• Superior cerebellar artery (SCA) (upper pons)

Medulla
• Anterior spinal artery (medial medulla)
• Posterior inferior cerebellar artery (PICA) (lateral medulla)
• Vertebral arteries (small branches)

The somatic motor system is concerned with voluntary skeletal movement. The basic pathways involves two motor neurons; Upper motor neurons (UMN) and Lower motor neurons (LMN). Coordinated movements also involve inputs from brainstem regions (navigational movements and posture), the cerebellum (corrective action) and basal ganglia (refinement of movement plans).

Function – Voluntary movement, especially distal limb control
Pathway – motor cortex --> Internal capsule --> Cerebral peduncles --> Pons --> Medullary pyramids (decussation occurs to form anterior and lateral corticospinal tracts)

Decussation – this means crossing over to the opposite side of the CNS, so the left hemisphere controls the right side of the body. Most fibres cross (90%) at the pyramidal decussation in the medulla to form the lateral corticospinal tract; uncrossed fibres form the anterior corticospinal tract.

Lateral = Limbs
Anterior = Axial muscles in neck and trunk

Function – Connects motor cortex to brainstem for voluntary control of cranial nerve motor nuclei for motor innervation of intrinsic and extrinsic tongue musculature (facial expression, speech and swallowing)

Pathway – Motor cortex (precentral gyrus) --> Internal capsule --> Brainstem (separate from corticospinal tract and synapse with the motor nuclei of cranial nerves in the pons and medulla) --> These cranial nerves control muscles of facial expression eg; hypoglossal nerve for tongue or trigeminal nerve for mastication

Function – Reflex head, neck and eye movements to visual/auditory stimuli

Pathway – Superior colliculus (midbrain) --> Decussates in dorsal tegmentum (central region of the brainstem) --> Descends to cervical spinal cord and LMNs (neck muscles)

Function – Posture, locomotion and muscle tone modulation

Pathway – Pontine reticulospinal (facilitates extensor tone) --> Medullary reticulospinal (inhibits extensor tone) --> descend ipsilitaerally and bilaterally to trunk and proximal limb LMNs

Function – maintain balance and posture in response to movement

Pathway – Lateral vestibulospinal tract is ipsilateral (no decussation) to all levels and activates extensors while the medial vestibulospinal is bilateral (both sides of body) to cervicalpper thoracic levels and controls head position. After leaving the vestibular nucleus it targets ventral horn LMNs of axial & limb extensors.

Function - Facilitates flexors, inhibits extensors (mainly upper limb).

Pathway - Originates in the red nucleus of the midbrain and targets LMNs in lateral ventral horn (upper limb flexors)

Classification of Cranial nerves: Remember Afferent = sensory information TO the brain and Efferent is motor information FROM the brain
- General somatic afferent (GSA) – sensory for skin
- General visceral afferent (GVA) – Internal sensation
- Special sensory afferent (SSA) – Smell, sight, taste and hearing
- General somatic efferent (GSE) – Motor to skin/muscles
- General visceral efferent (GVE) – internal motor (eg baroreceptors)

Oh
Oh
Oh
To
Touch
And
Feel
Very
Good
Velvet
And
Heaven

Some - Sensory
Say
Money - Motor
Matters
But - Both
My
Brother
Says
Big
Brains
Matter
More

Function: Olfactory nerve is a SSA with its sensory receptors located in the olfactory epithelium. It functions purely for sensory – smell. One of two cranial nerves with direct connection to the cerebrum, meaning it originates form the cerebrum rather than brainstem. Also is the only afferent not to bypass the thalamus

Pathway: Olfactory receptor cells in nasal mucosa (travel through foramen in the cribriform plate → ethmoid bone) → olfactory bulb → olfactory tract → primary olfactory cortex (temporal lobe).

Lesion: Anosmia (loss of smell) which can affect taste

Function: Optic nerve is a SSA with its photoreceptors located in the retina. With CNI, its the only nerve to orginate from the cerebrum

Pathway: Retina → optic nerve → optic chiasm (partial crossing) → optic tracts → lateral geniculate nucleus (thalamus) → primary visual cortex (occipital lobe).

Lesion: Complete or partial loss of vision

Function: Occulomotor nerve is a GSE and GVE with its somatic function innervating 4/6 extraocular eye muscles and the visceral function is parasympathetic to innervate sphincter pupillae (pupillary constriction) & ciliary muscle (accommodation).

Pathway: Midbrain (occulomotor nucleus (somatic) & Edinger–Westphal nucleus (visceral) ) → cavernous sinus → superior orbital fissure → eye muscles.

Lesion: Lesion to GSE = Ptosis (drooping eyelid), “down and out” eye position & Lesion to GVE = pupil dilation, diplopia (two images of a single object)

Function: Trochlear Nerve is a GSE that innervates the extraocular muscle, superior oblique. This muscle moves the eye down and in. The trochlea is a pulley-like structure made of cartilage that guides the superior oblique muscle

Pathway: Midbrain (dorsal surface) → passes around brainstem → superior orbital fissure → superior oblique

Lesion: Vertical diplopia (double vision) and inability to look down when the eye is adducted (superior oblique muscle action)

Largest cranial nerve with as well as motor information to the muscles of mastication (V3). It has three main branches:
- Ophthalmic (V1) for sensory information (GSA)
- Maxillary (V2) for sensory information (GSA)
- Mandibular (V3) for both sensory and motor information (GSA & GSE)

The sensory components originate from the trigeminal ganglion and the motor component originates from the motor nucleus in the pons
V1: Eyes --> Conjunctiva --> Lacrimal gland --> nasal cavity --> frontal and ethmoid sinuses --> upper eyelid --> Dorsum of nose
V2: Dura in anterior/middle cranial fossa --> Nasopharynx --> Palate --> Nasal cavity --> Teeth (maxilla) --> Maxillary sinus --> Skin (nose, cheek, upper lip, lower eyelid)
V3: Foramen ovale --> Lower jaw sensation + motor to muscles of mastication (temporalis, masseter, medial and lateral pterygoid)

Lesion: Loss of facial sensation and motor function for mastication

Function: Abducens nerve is a GSE that innervates the last extraocular eye muscle - lateral rectus

Pathway: Pons → Cavernous sinus → Superior orbital fissure → lateral rectus

Lesion: No lateral eye movement

Function: Facial Nerve has five branches for multiple modalities (GSE, GVE, GSA, SSA). The branches can be remembered by the mnemonic Two Zebras Bit My Cat, the main functions of the facial nerve include taste to anterior 2 / 3 of tongue, facial expression and parasympathetic fibres to lacrimal and salivary glands

Pathway: Pons → internal acoustic meatus → facial canal → stylomastoid foramen → 5 branches (Temporal, Zygomatic, Buccal, Mandibular, Cervical).

Lesion: Loss of taste on anterior 2 / 3 of tongue, Paralysis of facial muscles (bells palsy), dry mouth or eyes

Function: The vestibulocochlear nerve is a SSA responsible for balance and spatial orientation. It uses the vestibular apparatus (eg; semicircular canals) and cochlear / vestibular nucleus' in the CNS

Pathway: Inner ear (cochlea, semicircular canals) → internal acoustic meatus → brainstem (pons/medulla).

Lesion: Hearing loss, vertigo, imbalance

Function: The glossopharyngeal nerve is a GVA, SSA, GVE and GSE fibres for mixed functions.
GVA = Carotid body and sinus, palatine tonsils, upper pharynx
SSA = taste on posterior 1/3 of tongue (somatic + special)
GVE – Parotid salivary gland
GSE – Stylopharyngeus muscle (elevating and widening pharynx and larynx for swallowing/speaking)

Pathway: Medulla → jugular foramen → tongue & pharynx.

Lesion: Loss of gag reflex, loss of taste on posterior tongue, dry mouth

Function: The vagus nerve is a large mixed modality nerve mainly for parasympathetic function (efferent)
GSE – Muscles of pharynx, larynx and soft palate.
GVE – Smooth muscles and glands in the pharynx, larynx, abdominal and thoracic vertebra
GVA – baroreceptors in aortic arch, mucous membranes of lungs, heart, abdominal viscera, pharynx, larynx and oesophagus
GSA – Skin posterior ear, dura in posterior cranial fossa
SSA – Taste in the epiglottis

Pathway: Medulla → jugular foramen → neck, thorax, abdomen.

Lesion: Soft palate deviation, vocal cord paralysis, loss of parasympathetic function

Function: The accessory nerve is a General somatic efferent (GSE) responsible for innervating sternocleidomastoid and trapezius muscles

Pathway: Spinal roots (C1–C5) → foramen magnum → joins cranial root briefly → exits via jugular foramen → SCM & trapezius.

Lesion: Weak shoulder shrug and head turning movements

Function: The hypoglossal nerve is a General somatic efferent (GSE) providing sensation to intrinsic and extrinsic tongue muscles

Pathway: Medulla (hypoglossal nucleus) → hypoglossal canal → tongue.

Lesion: Muscle atrophy, speech disturbance, tongue deviates toward lesion side, difficulty swallowing

CNI = Cribiform plate in ethmoid bone
CNII = Optic Canal
CNIII, CNIV, CNV (v1) & CNVI = superior orbital fissure
CNV (v2) = foramen rotundum
CNV (v3) = foraman ovale
CNVII and CNVIII = internal acoustic meatus
CNIX, CNX, CNXI = Jugular foramen (CNXI Originates from spinal cord (C1–C5) → enters skull via foramen magnum → then exits through jugular foramen)
CNXII - Hypoglossal canal

Ventral horn is the grey matter forming the anterior section of the spinal cord, containing cell bodies of LMNs, functioning to send motor output to skeletal muscles. The axons exit via ventral roots

Dorsal Horn is the grey matter forming the posterior section of the spinal cord which contains interneurons and sensory relay neurons, functioning to receive sensory input from dorsal roots - that is the sensory axons entering the spinal cord

Anterior median fissure is a deep groove along the midline of the spinal cord which functions to allow passageway of blood vessels into SC

The central canal is a narrow canal running through the centre of the spinal cord which is filled with cerebrospinal fluid (CBF), which thus functions to circulate CBF, providing cushioning and nutrient transport

The dorsal horn carries interneurons recieving input from somatic and visceral sensory neurons. Somatic sensory is at the top of the horn, with visceral sensory below it

The ventral horn carries visceral motor and somatic motor neurons ready to recieve the sensory information relayed from the interneurons between the sensory neurons of the dorsal horn. These motor neurons will then leave the spinal cord (CNS) via the ventral root. Visceral is ontop of the somatic motor neurons in this.

Think Visceral sensory and motor are paired in middle with the somatic GSE / GSA at the top of their horns respectively.

Two types of arterial supply in the spinal cord; Longitudinal arteries and segmental arteries.
Longitudinal arteries run the length of the cord while segmental / radicular arteries reinforce the spinal cord along the way

Anterior Spinal artery
- Formed by branches of each vertebral artery at the medulla, running down the anterior median fissure.
- Supplies the anterior 2/3rds of the spinal cord (including ventral horns).

Posterior spinal arteries (2)
- Arise from vertebral arteries (sometimes Posterior inferior cerebellar artery or PICA)
- Run along posterolateral sulci of spinal cord
- Supply posterior 1/3 of cord

- Enter via intervertebral foramina to reinforce longitudinal arteries. These then bifurcate (divide) into anterior and posterior radicular arteries to supply the roots of the spinal cord
(Start as segmental arteries of the aorta then split into radicular when close to the spinal cord)

- Examples include artery of Adamkiewicz aka the great anterior segmental medullary artery which arises from lower thoracicpper lumbar aorta and is a major supply to lumbar enlargement

Lens - a transparent bi-convex disc that focuses light onto the retina and is responsible for accommodation (the process whereby the eye is fine tuned or the curvature of the lens changes for near & far distances)

Pupil – The opening of the eye in the centre of the iris responsible for regulating the amount of light entering the eye. Constriction = less light and dilation = more light

Ciliary muscle – the smooth muscle ring around the lens which controls lens shape via suspensory ligaments (zonules)

Retina – innermost neural layer at the back of the eye which contains photoreceptors (rods and cones) that convert light into neural signals for the optic nerve

Cornea – a transparent dome-shaped outer layer covering the iris and pupil. It’s the primary refractive surface for the eye (bends incoming light to focus on retina)

Fovea – small central pit in macula of retina which is the area of highest visual acuity, meaning it is the highest in cones (photoreceptors receiving colour) and NOT Rods

Optic Nerve (CN II) – a cranial nerve that exits retina at the optic disc transmitting cisual information to ganglion cell axons in the brain for processing in the visual cortex (occipital lobe)

Accommodation refers to the ability of the lens to change its curvature (convexity) to focus on objects at any distance.

For Distant vision: The light rays entering the eye are more or less parallel, and do not need to be converged sharply. The ciliary muscles relax, drawing the sclera back and causing the suspensory ligaments to be pulled taut. This lengthens the lens (flattening it), decreasing the curvature and reducing refractive power of the lens.

For Near vision: The light rays must be refracted more. The ciliary muscles contract (towards lens), drawing the sclera forward and causing the suspensory ligaments to slacken. This makes the lens rounder, increasing the curvature (concavity) and thus the refractive power of the lens.

Myopia (short-sightedness) = eye can focus on near objects, but the focal length when viewing distant objects is too short. The causes include:
● Eyeball too elongated so image falls in front of retina
● Lens cannot become thin enough to focus distant objects (lens is too rounded - convex)
● Refractive power of cornea is too great

Hyperopia (long-sightedness) = eye can focus on distant objects, but the focal length when viewing near objects is too long. The causes Include:
● Eyeball is too short so image falls behind retina
● Lens cannot become round enough to focus close objects (concave)
● Refractive power of cornea is inadequate

Cataracts = any loss of transparency of the lens, causing blindness if untreated. The causes Include:
● Ageing process
● Congenital (birth) abnormalities
● Disease e.g. diabetes or glaucoma

Rods
- Approximately 120 million and has a high distributed throughout the peripheral retina except at the fovea
- Functions for night vision and motion detection only picking up grey and black (monochrome) EM waves. These are highly sensitive, picking up low light

Cones
- Approximately 6 million and has a low distribution throughout the retina except at the fovea (central retina)
- Functions for colour vision picking up RBG EM waves (trichromatic vision) and has low sensitivity, meaning it only picks up bright light

This is the process in the eye's photoreceptor cells (rods and cones) where light energy is converted into an electrical signal that the brain can understand.

(light = hyperpolarisation whereas dark = depolarisation)

1. cGMP levels are higher in outer segments and these bind to Na channels keeping NA channel open

2. This allows the influx of Na for photoreceptor depolarization

3. This AP releases neurotransmitters from the terminal of the neuron

1. cGMP levels in the outer segment drop in the presence of light due to activation of rhodopsin

2. cGMP no longer binds to Na channels and thus these channels close

3. An increased negative charge occurs causing photoreceptor hyperpolarisation meaning there is no neurotransmitter release

4. Hyperpolarization reduces/inhibits glutamate release. This decrease in glutamate triggers an excitatory response in ON bipolar cells and an inhibitory response in OFF bipolar cells, allowing for the transmission of visual information to the brain at synapse so the signal is then relayed to bipolar cells → ganglion cells → optic nerve.

Bipolar cells are interneurons in the eye's retina that relay visual information from photoreceptor cells (rods and cones) to retinal ganglion cells, which then send signals to the brain.

- ON bipolar cells respond to light and cause depolarisation (excitatory response) as their metabotropic glutamate receptors (mGluRs) are blocked in the absence of glutamate release causing a conductance increase = depolarisation.

- OFF bipolar cells respond to dark and cause depolarisation in dark in response to glutamate release and hyperpolarisation in light due to an absence of glutamate = ionotropic channels close

1. Photoreceptors (rods and cones) detect light and synapse on bipolar cells (interneurons)

2. These bipolar cells synapse with retinal ganglion cells (RGCs) which axons form the optic nerve (CNII)

3. At the optic chiasm, nasal retinal fibers cross whilst temporal fibers remain ipsilateral

4. These fibres continue as the optic tract until they synapse in lateral geniculate nucleus (LGN) of the thalamus

5. LGN then transmits this information to the primary visual cortex in the occipital lobe.

Fungiform Papillae
• Mushroom-shaped, scattered across anterior 2/3 of tongue.
• Contain taste buds.

Circumvallate (Vallate) Papillae
• Large, dome-shaped, arranged in a V-shape near posterior tongue.
• Contain most of the taste buds.

Foliate Papillae
• Leaf-like ridges on lateral tongue (posterior).
• Contain taste buds, more prominent in children.

Filiform Papillae
• Thin, conical, cover most of tongue surface.
• No taste buds – mechanical role (friction, texture).

Fat C*nts Find Food

1. Taste receptors in taste buds (on papillae) detect taste (sweet, sour, salty, bitter or umami)

2. These signals are carried by cranial nerves 7, 9 and 10. The facial nerve carries taste through Chorda tympani for the anterior 2/3 of tongue, the glossopharyngeal carries taste for the posterior 1/3 of tongue and the vagus nerve is responsible for taste in the epiglottis and pharynx

3. These nerves project to the solitary nucleus in medulla (gustatory nucleus)

4. From here the information is given to the ventral posterior medial (VPM) nucleus of the thalamus

5. VPM → Primary Gustatory Cortex (insula + frontal operculum).

To Hypothalamus: regulates feeding behavior (hunger/satiety, homeostasis).

To Amygdala: links taste to emotion (e.g., disgust, cravings, aversion).

To Orbitofrontal Cortex: integrates taste with smell and vision → perception of flavor

To Brainstem Autonomic Centers: influences salivation, gag reflex, digestive secretions

Olfactory receptor neurons (ORNs) are chemoreceptors and bipolar cells located in the olfactory epithelium. These bipolar neurons have:
- an apical dendrite which projects into the nasal cavity and ends in the olfactory knob with cilia projections that contain odorant receptors.
- a cell body embedded in olfactory epithelium
- a basal axon that passes through the cribriform plate of the ethmoid bone and synapses in olfactory bulb (Projects in olfactory bulb and through cribriform plate)

Smell is the only sense that DOES NOT project to thalamus before cortex.
1. Odorant molecules dissolve in mucus and bind to G-protein coupled receptors on cilia

2. Signal transduction occurs causing the depolarization of olfactory receptor neurons

3. Axons of ORNs bundle to form the olfactory nerve (CNI) and passes through the cribriform plate, synapsing at the olfactory bulb.

4. Within the bulb, the ORN axons synapse onto mitral and tufted cells in glomeruli. These mitral/tufted cell axons form the olfactory tract

5. These fibres directly project to primary olfactory cortex (no thalamic relay) which includes the piriform cortex in temporal lobe, amygdala, olfactory tubercle and entorhinal cortex.

The olfactory bulb targets the piriform cortex which then sends information to the orbitofrontal cortex which integrates olfaction with taste → perception of flavor.

The olfactory bulb targets the amydala / olfactory tubercle which links odors to emotions (e.g., fear, disgust, comfort). It also sends information to the Hypothalamus which influences feeding, salivation, appetite, and autonomic responses and the orbitofrontal cortex for taste / flavour perception

Lastly, information from the entorhinal cortex (part of olfactory cortex) sends information to the hippocampus to form a strong link between smell & memory

- Special receptors are located in head and relate to vision, hearing, balance, olfaction and taste eg; retinal photoreceptors (rods and cones). These have very complex apparatus and nerve endings

- General receptors are located all over the body and are activated by touch, temperature, pain and movement eg; mechanoreceptors in skin

• Mechanoreceptors – touch, pressure, vibration, stretch (e.g., Pacinian corpuscles, Meissner’s corpuscles).
• Thermoreceptors – temperature changes.
• Chemoreceptors – pH, O₂, CO₂, taste, smell.
• Photoreceptors – light (rods and cones).
• Nociceptors – pain (mechanical, thermal, chemical damage).
• Proprioceptors – specialised mechanoreceptors giving body position sense

Proprioceptors (specialized mechanoreceptors giving body position sense):
• Muscle spindles – detect muscle length/stretch.
• Golgi tendon organs – detect muscle tension/force.
• Joint receptors – detect joint position & movement.
• Low threshold mechanoreceptors (LTMs) – Ruffini ending and Pacinian corpuscles

Proprioceptive information ascends in dorsal column medial leminscal pathway then synapses at:
Gracile nucleus – lower limbs and torso (in medulla)
Cuneate nucleus – upper limbs and torso
Trigeminal nucleus – face

This information is then projected to primary somatosensory cortex

1. Nociceptors activated → first-order neuron (Aδ fibers = fast (20m / s) sharp; C fibers = slow (2 m / s, polymoidal receptor).

2. Synapse in dorsal horn.

3. Second-order neuron decussates in spinal cord.

4. Ascends via spinothalamic tract (lateral = pain, temperature whilst anterior = crude touch and pressure) → thalamus → primary somatosensory cortex & limbic areas.

Corticospinal Tract
- Carries motor commands - the lateral CT controls lower limb while the anterior CT carries upper limb
- Decussates at the pyramids of medulla
- Delivers information to motor cortex

Spinothalamic Tract
- Carries sensory infromation such as pain, touch and temperature - lateral = pain and temp while anterior = crude touch and pressure
- Decussates at spinal cord
- Delivers sensory information to the somatosensory cortex

Dorsal column
- Carries sensory information from the dorsal root
- Decussates at medulla oblongata
- Delivers sensory information

Cochlea - Spiral-shaped organ filled with fluid and lined with hair cells that converts vibrations into electrical signals

Ossicles - Three tiny bones in the middle ear consisting of the malleus (hammer), the incus (anvil), and the stapes (stirrup). These bones amplify the vibrations and continue to allow the sound energy to be efficiently transmitted and amplified to the fluid-filled Cochlea via the oval window.

External auditory meatus (EAM) - The canal leading from the outer ear to the tympanic membrane (eardrum), directing sound to it. This is lined with skin, hair, sebaceous glands and ceruminous glands (producing earwax).

The cochlea lies in the petrous part (bony labriynth) of the temporal bone and has three fluid-filled compartments
- Scala vestibuli (upper): Carries high Na and low K fluid (perilymph)
- Scala tympani (lower): Carries high Na and low K fluid (perilymph)
- Scala media (cochlear duct): Carries high K and low Na fluid (endolymph)

These are divided by two membranes:
- Reissner’s (vestibular) membrane separating scala vestibuli from scala media

- Basilar membrane separating scala media/cochlear duct from scala tympani and supports the organ of Corti

The organ of Corti sits on top of the basilar membrane and contains three rows of outer cells for detection and amplification of sound then one row of inner hair cells for fine discrimination

Sound Waves Enter the Ear or EAM:
• Pinna: The process begins when sound waves are collected by the pinna (the outer part of the ear). The pinna's shape helps funnel these sound waves into the ear canal/EAM.
• EAM: The sound waves travel down the ear canal, directing them towards the ear drum (tympanic membrane).

Sound Waves to Mechanical Energy:
• Tympanic membrane: When the sound waves reach the eardrum, they cause it to vibrate. The eardrum transforms the sound wave energy (acoustic energy) into mechanical energy through its vibrations.
• Ossicles (Hammer, Anvil, and Stirrup): The vibrating eardrum is connected to a series of three tiny bones in the middle ear: the hammer (malleus), anvil (incus), and stirrup (stapes). The eardrum's vibrations are transmitted to the hammer, which then passes these vibrations to the anvil and then to the stirrup. These bones amplify the vibrations and continue to transmit the mechanical energy.

Mechanical Energy to Fluid Waves:
• Stirrup and Oval Window: The stirrup / stapes is connected to the oval window, a membrane-covered opening that leads into the cochlea. When the stirrup vibrates, it pushes on the oval window, creating pressure waves in the perilymph of scala vestibuli.
• Cochlea: Inside the cochlea, the fluid waves move through the spiral structure and basilar membrane, causing the hair cells / stereocilia (specialized sensory cells) to move.

Mechanical Energy to Electrical Signals (mechanotransduction):
• Hair Cells in Cochlea: As the fluid waves move through the cochlea, they cause the tiny hair cells lining the cochlea to bend. The bending of these hair cells opens mechanically gated K channels causing an influx of K from endolymph (high in K) to depolarise the hair cell due to unqiue inner ear concentrations
• Voltage-gated Ca channels open causing glutamate release (neurotransmitter) onto spiral ganglion neurons. This ultimately converts the mechanical energy into electrical energy through the generation of an AP.

Electrical Signals to the Brain:
• Auditory Nerve: The electrical signals or APs generated by the hair cells are then transmitted to the brain through the auditory nerve.
• Brain Interpretation: The brain receives and interprets these electrical signals as sound, allowing us to perceive and recognize what we hear.

Na influx = cell depolarisation or TMP becomes more positive
K Influx = cell depolarisation or TMP becomes more positve
Na efflux = cell repolarisation or TMP becomes more negative
K efflux = cell repolarisation or TMP becomes more negative

Remember Na and K are cations or positive ions, thus if entering a cell will make it more positive or if leaving more negative

1. Hair cells → spiral ganglion cells → cochlear nerve (CN VIII).

2. Synapse in cochlear nuclei (medulla).

3. Bilateral projections to superior olivary complex in medulla (important for sound localisation).

4. Ascend via lateral lemniscus → inferior colliculus (midbrain).

5. Project to medial geniculate nucleus (MGN, thalamus).

6. Final projection to primary auditory cortex (Heschl’s gyrus, temporal lobe).

Tonotopy is the frequency-to-place mapping in the auditory system, where different locations in the brain and ear are specialized for processing sounds of different frequencies

The base (inner most part) of the cochlea detects low-frequency sounds while the outer part detects high frequency sounds

The most lateral part of the temporal lobe = low frequnecy while medial = high frequency sounds

Semicircular Canals
- Three canals – Anterior, posterior and lateral
- Each canal has a dilated region at its base called the ampulla, which contains the crista ampullaris
- The semicircular canals function to detect angular and rotational acceleration (head turns, nods and tilts)

Utricle
- Located in the vestibule it contains the macula utriculi
- This functions to detect horizontal linear acceleration eg; moving forward in a car

Saccule
- Also in the vestibule, adjacent to the utricle this contains macula sacculi
- Functions to detect vertical linear acceleration eg; moving in an elevator + Gravity

Crista ampullaris (in semicircular canals):
o Contains hair cells embedded in a gelatinous structure called the cupula.
o Cupula bends with fluid (endolymph) movement when head rotates.

Maculae (in utricle & saccule)
o Hair cells embedded in a gelatinous membrane that contains otoliths (calcium carbonate crystals).
o Otoliths add weight, making maculae sensitive to gravity and linear acceleration.

Therefore, Crista ampullaris detects rotation and has no otoliths while macule features otoliths and detects linear acceleration and head position relative to gravity

Hair cells are the sensory receptors (like in cochlea).

Stereocilia deflected by cupula (semicircular canals) or otolithic membrane (utricle/saccule).

Deflection towards kinocilium (specialised stereocilia) → opens K⁺ channels → depolarisation → glutamate release → ↑ firing rate of vestibular nerve fibers (excitation)

Deflection away from kinocilium → hyperpolarisation → ↓ firing rate (inhibition)

Signals carried by vestibular portion of CN VIII → vestibular nuclei (brainstem) and cerebellum.

The Nasal cavity is the uppermost part of the respiratory tract and its functions to filter, warm and moisten air entering the airways. Features very light and fragile bones with open spaces known as sinuses.

1. Nasal Vestibule – lined by skin and hair follicles

2. Respiratory region – lined by respiratory epithelium with rich neurovascular supply

3. Olfactory region – lined by olfactory epithelium containing olfactory receptors

• Anteriorly – opens at the nares (nostrils) and is seperated by nasal septum

• Posteriorly – communicates with the nasopharynx via the choanae (opening between nasal cavity and nasopharynx)

• Roof – formed by nasal, frontal, ethmoid (cribriform plate), and sphenoid bones.

• Floor – mainly palatine process of maxilla and horizontal plate of palatine bone (hard palate).

The lateral wall has three curved shelves known as conchae (turbinate) which are covered with mucosa and opens to the nasopharynx via choanae
- Superior
- Middle
- Inferior

Conchae increase surface area, create turbulence and help warm, humidify and filter air. Beneath each conchae lies a meatus (four air chambers) that drains sinuses and ducts.
- Superior Meatus
- Middle meatus
- Inferior meatus

Olfactory nerve (CN I):
• Olfactory receptor neurons in the roof of the nasal cavity (olfactory epithelium) passing through cribriform plate (ethmoid bone).
• Function: smell

Trigeminal nerve (CN V):
• V1 (ophthalmic branch, via nasociliary nerve): sensation from anterior-superior nasal cavity.
• V2 (maxillary branch, via nasopalatine and greater palatine nerves): General sensation from posteroinferior nasal cavity.
• Function: general sensation (touch, pain, temperature)
.
Autonomic nerves (via pterygopalatine ganglion - Facial Nerve):
• Parasympathetic (Facial Nerve – CN VII → greater petrosal nerve): controls secretions from nasal glands
• Sympathetic (via deep petrosal nerve): regulates blood flow in mucosa.

Arterial supply is from branches of both internal and external carotid arteries. The main include:
• Anterior & posterior ethmoidal arteries (ophthalmic artery, ICA branch)

• Sphenopalatine artery – largest vessel (terminal branch of maxillary artery, ECA branch)

• Greater palatine artery - gums of teeth (gingiva) (branch of maxillary artery).

• Superior labial artery (facial artery).

• These form Kiesselbach’s plexus (Little’s area) on the anterior septum — common site of epistaxis (nosebleeds).

Air-filled spaces within certain cranial bones, lined by respiratory mucosa that is ciliated to lighten skull, produce mucus and add resonance to voice. Four pairs:
• Frontal sinuses – in frontal bone; drain into middle meatus.

• Ethmoidal air cells – anterior, middle, posterior; drain into middle & superior meatus.

• Maxillary sinuses – in maxilla (largest); drain into middle meatus (note: drainage is high on the medial wall, making them prone to infection).

• Sphenoidal sinuses – in body of sphenoid located posterior to spheno-ethmoidal recess; drain into sphenoethmoidal recess.

The nasopharynx is the first part of the pharynx and is located posterior to choanae and superior to the soft palate. It features mucosal elevations and folds covering various openingd and muscles including the pharyngotympanic (audiotory) tube

1. Oral Vestibule – region between dental arches and the lips and the cheeks
2. Oral cavity proper – lies within the confines of teeth

Roof – hard palate (maxilla & palatine bones) and soft palate (continuation of hard palate - muscle). Palate seperates oral cavity from nasal cavity

Floor - two suprahyoid muscles – mylohyoid, geniohyoid muscles).

Lateral wall – cheek muscles – Buccinator

Anterior wall – lips

Extrinsic muscles (change position of tongue) innervated by hypoglossal nerve except palatoglossus. SH (shh) PG

• Styloglossus – retracts and elevates tongue, from styloid process

• Hyoglossus – depresses tongue, from hyoid bone

• Palatoglossus – elevates posterior tongue (innervated by CN X, not CN XII), from soft palate

• Genioglossus – protrudes tongue and depresses centre, from mandible

Intrinsic muscles (change shape of tongue):
- superior / inferior longitudinal (2 muscles)
- transverse
- vertical

• Motor:
o All muscles (both intrinsic and extrinsic) supplied by CN XII (hypoglossal) except palatoglossus (CN X).

• Sensory:
o Anterior 2/3: General sensation (lingual nerve, V3 of trigeminal), Taste (chorda tympani, CN VII – facial nerve).
o Posterior 1/3: Taste Glossopharyngeal (CN IX).
o Root/epiglottis: CN X.

Parotid gland:
• Location: anterior/inferior to ear, overlying masseter.
• Duct opens opposite 2nd upper molar.
• Parasympathetic innervation: CN IX (glossopharyngeal) via otic ganglion → auriculotemporal nerve. The facial nerve pierces through but does not innervate it

Submandibular gland:
• Beneath mandible, duct opens beside lingual frenulum.
• Parasympathetic innervation: CN VII (Facial Nerve – chorda tympani via lingual nerve).

Sublingual gland:
• Floor of mouth under tongue.
• Parasympathetic innervation: CN VII (Facial Nerve – chorda tympani via lingual nerve)

Masseter
• Origin: zygomatic arch.
• Insertion: lateral surface of mandibular ramus.
• Action: elevates mandible (closes jaw).

Temporalis
• Origin: temporal fossa.
• Insertion: coronoid process of mandible.
• Action: elevates and retracts mandible.

Medial pterygoid
• Origin: medial surface of lateral pterygoid plate (most lateral projection of pterygoid process of sphenoid bone)
• Insertion: medial surface of mandibular ramus.
• Action: elevates mandible, side-to-side grinding.

Lateral pterygoid
• Origin: lateral surface of lateral pterygoid plate (most lateral projection of pterygoid process of sphenoid bone)
• Insertion: neck of mandible & articular disc of TMJ.
• Action: protrudes mandible, side-to-side movement.

Visceral - most anterior and central covered by pretracheal fascia

Vertebral - largest, most posterior containing spinal cord, cervical vertebrae and associated muscles. Covered by prevertebral sheath

Vascular x2 - Covered by paired carotid sheaths on either side of the neck, which contains common carotid, internal jugular and vagus nerve

Anterior compartment contains
- Hyoid muscles – suprahyoid and infrahyoid
- Platysma
- Carotid arteries – common carotid and internal carotid
- Internal jugular vein
- Nerves (Facial, glossopharyngeal, vagus, accessory and hypoglossal)
- Thyroid gland

Boundaries (anterior triangle):
• Anterior border of sternocleidomastoid – separating anterior and posterior compartments
• Midline of neck (medial)
• Inferior border of mandible (superior)

Posterior compartment contains
- Hyoid muscle – Omohyoid
- Other muscles – Splenius capitus, levator scapulae and scalenes
- External jugular vein
- Nerves (accessory and brachial plexus)

Boundaries (Posterior triangle):
• Posterior border of Sternocleidomastoid (anterior)
• Anterior border of trapezius (posterior)
• Middle third of clavicle (inferior)

The thyroid gland is a large endocrine gland laying in the anterior triangle (C5-T1) that regulates metabolism and calcium homeostasis. It has a visceral compartment made up of two lobes and receives its blood from the superior and inferior thyroid arteries

The hyoid bone is a U-shaped muscle at C3 level that does not articulate with any other bones. It has two arms – greater and lesser horns which provides attachment points for many muscles and structures in the head and neck.

Suprahyoid muscles (elevate hyoid, assist swallowing): Miss Dig (MS DG)

• Digastric (ant. belly CN V v3, post. belly CN VII) – Lowers mandible and raises hyoid, posterior belly pulls hyoid up and back

• Stylohyoid (CN VII) – pulls hyoid back

• Mylohyoid (CN V v3) – elevates hyoid (forms floor of oral cavity

• Geniohyoid (C1 via CN XII) – pulls hyoid forward when mandible is fixed and mandible down when hyoid is fixed (forms floor of oral cavity)

Innervation = T F T F + HYPOGLOSSAL

Infrahyoid muscles (depress hyoid/larynx): TOSS

• Sternohyoid (C1-3) – depresses hyoid after swallowing

• Omohyoid (C1-3) – depresses and fixes hyoid

• Sternothyroid (C1-3) – draws larynx downward

• Thyrohyoid (C1) – depresses and fixes hyoid, raises larynx during swallowing.

• All innervated by ansa cervicalis except thyrohyoid = C1 via CN XII (hypoglossal Nerve). The ansa cervicalis is a neural loop in the neck formed by branches from the cervical plexus, specifically spinal nerves C1-C3

The common carotid artery bifurcates at C3-C4 into the internal carotid and external carotid. The internal carotid goes staright to the brain while the external carotid branches up the neck.
1. Superior thyroid (SOME)
2. Ascending pharyngeal (ANCIENT)
3. Lingual (LOVERS)
4. Facial (FIND)
5. Occipital (OLD)
6. Posterior auricular (POSITIONS)
7. Maxillary (MORE)
8. Superficial temporal (STIMULATING)

• External jugular vein (EJV): drains skull/face → subclavian vein

• Internal jugular vein (IJV): drains brain & superficial face/neck → brachiocephalic vein (junction between subclavian and internal jugular veins)

CN VII (Facial) - stylomastoid foramen, innervating posterior belly of digastric and stylohyoid

CN IX (Glossopharyngeal) - jugular foramen to stylopharyngeus & pharynx

CN X (Vagus) - Jugular foramen to larynx, pharynx and palatoglossus

CN XI (Accessory) - Jugular foramen to sternocleidomastoid and trapezius

CN XII (Hypoglossal) - Hypoglossal canal to tongue muscles except palatoglossus, geniohyoid

1. Nasopharynx:
• Superior → base of skull
• Inferior → soft palate
• Anterior → posterior nasal choanae
• Posterior → pharyngeal wall
• Contents: pharyngeal tonsil (adenoids), opening of pharyngotympanic (eustachian) tube

2. Oropharynx:
• Superior → soft palate
• Inferior → superior border of epiglottis
• Anterior → oral cavity (via oropharyngeal isthmus)
• Posterior → pharyngeal wall
• Contents: palatine tonsils, lingual tonsil.

3. Laryngopharynx (hypopharynx):
• Superior → epiglottis
• Inferior → cricoid cartilage (C6) → continues as oesophagus
• Anterior → laryngeal inlet
• Posterior → pharyngeal wall
• Special feature: piriform recesses (common site of food lodgement).

The pharynx has three outer circular muscles known as constrictors which all function to constrict the pharynx. These are innervated by Vagus nerve

The pharynx also has an inner layer of three longitudinal muscles which function to shorten and elevate the pharynx during swallowing and speaking
- Salpingopharyngeus = elevation of pharynx + opening of eustachian tube (CN X)
- Palatopharyngeal = elevation of pharynx (CN X)
- Stylopharyngeus = elevation of pharynx (CN IX)

Vallecula (between tongue and epiglottis).

Piriform recess (small depression in laryngopharynx, lateral to laryngeal inlet).

The pharynx is mainly supplied by the ascending pharyngeal artery (a branch of the external carotid artery). It also recieves contributions from facial artery, maxillary artery, lingual artery and superior / inferior thyroid artery

Veins drain from the face into the the pharyngeal venous plexus which drains into the internal jugular vein

Motor Innervation:
All muscles of the pharynx are innervated by the Vagus Nerve (CN X) except the stylopharyngeus which is innervated by the glossopharyngeal nerve (CN IX)

Sensory Innervation:
Nasopharynx = Trigeminal v2, Oropharynx = Glossopharyngeal Nerve, Laryngopharynx = Vagus Nerve

The larynx is essential for phonation (the production of voice) and is a component of the upper respiratory tract. It is found in the anterior neck, in the visceral compartment covered by pretracheal fascia

- Approximately at C3 (Hyoid bone) to C6 (largynotracheal junction)

The larynx is composed of 9 cartilage -3 unpaired and 3 paired

1) Thyroid cartilage - largest, forming the laryngeal prominence or Adams apple. Has two horns

2) Cricoid cartilage - ring-shaped cartilage that froms the base of the larynx. It has a complete ring sitting at C6 (above the trachea but below the thyroid cartilage)

3) Epiglottis - Leaf-shaped cartilage that folds back during swallowing to cover inlet and prevent food and liquid from entering airway

1) Arytenoid cartilages - a pyramid-shaped cartilage that anchors the vocal cords. Its base articulates with cricoid

2) Corniculate cartilages - small cartilages sitting on arytenoids, articulating with its apex (top)

3) Cuneiform cartilages - embedded in aryepiglottic folds or the fibroelastic membrane of larynx to provide support

We have two laryngeal ligaments – Vocal and Vestibular ligaments. These hold the vocal and vestibular folds in place, providng structure and support for phonation

• Vocal ligaments (true cords):
o Stretch from thyroid cartilage → arytenoid cartilage.
o Vibrate to produce sound.

• Vestibular ligaments (false cords):
o Superior to vocal ligaments.
o Protect airway, minimal role in phonation.

Rima glottis = opening between vocal folds (mucous membrane) and the arytenoid cartilages

Posterior cricoarytenoid - Only abductor of vocal cords

Lateral cricoarytenoid - Adductor of vocal cords for the clsing of rimma glottis

Transverse arytenoids and Oblique arytenoids - adducts arytenoid cartilages to close the rima glottis

Cricothryoid - tenses and elongates vocal cords for higher pitch

Thyroarytenoid - relaxes vocal cords for lower pitch

Vocalis - fine control of tension in cords

Two main arteries

1) Superior laryngeal artery - a branch of superior thryoid from the external carotid

2) Inferior laryngeal artery - a branch of inferior thyroid from thyrocervical trunk off the subclavian artery

1) Superior laryngeal vein - flows to superior thyroid into the internal jugular vein

2) Inferior laryngeal vein - flows to inferior thyroid vein into the brachiocephalic vein
- the brachiocephalic vein is the joining of the internal jugular and subclavian

Muscles of the Larynx are innervated by branches of Vagus (X) by two branches.
- Recurrent laryngeal nerve (CN X): supplies all intrinsic muscles except cricothyroid. This nerve originates in neck and ascends after passing inferiorly to subclavian
- External branch of superior laryngeal nerve (CN X): supplies cricothyroid. This nerve originates in thorax and ascends after passing aortic arch

For sensory innervation
Above vocal cords → internal branch of superior laryngeal nerve (CN X).
Below vocal cords → recurrent laryngeal nerve (CN X).

The thoracic inlet – first rib, T1 and manubrium

The thoracic outlet – costal margin, T12 Vertebra and 12th Ribs – filled by diaphragm

Diaphragm is innervated by phrenic nerves (C3-C5). It recieves its blood from inferior and superior phrenic arteries

Intercostals are innervated by intercostal nerves (T1-T11) and recieve their blood supply from anterior and posterior intercostal arteries. The anterior intercostal artery is a branch off the aorta whilst the posterior intercostal artery is a branch off the internal thoracic artery

Costal pleura - along ribs and sternum

Mediastinal pleura - along mediastinum

Diaphragmatic pleura - covering diaphragm

Cervical pleura - extends into root of neck above first rib

The right Lung has three lobes - Superior, middle and inferior. Seperated by two fissures. Horizontal fissure seperates superior and middle lobe while oblique fissure seperates middle and inferior lobes.

The left lung is smaller due to space for the heart. It has two lobes, superior and inferior and only one fissure - the oblique fissure.

The root of the lung is the tubular collection of structures that attach to the lungs including; pulmonary artery, pulmonary vein, main bronchus, bronchial artery / veins, and nerves / lympahtics
- The hilum is the depression in the surface of the lung where root structures enter the lung

The trachea (or windpipe) is a flexible tube that extends from the Larynx (C6) to carina (T4-T5) where it bifurcates into right and left primary bronchi. The trachea is reinforced by the C-shaped hyaline cartilage rings in which open posteriorly but are encased by trachealis muscle.

The trachea is also lined by respiratory epithelium (ciliated pseudostratified columnar epithelium with goblet cells)

The right lung has 10 segments whereas the left lung has 8-10 segments with some of them often fused

The lungs have two types of blood supply - one for gaseous exchnage and the other for nutrient supply.
- Pulmonary ciriculation is for gaseous exchange
- Bronchial circulation is for nutrional supply, involing bronchial arteries which aris from thoracic aorta to provide lung tissue. Bronhcial veins drain into azygous and hemiazygous veins

The lungs and innervated by the ANS:
Parasympathetic (Vagus nerve – CN X)
• Bronchoconstriction (narrowing bronchioles for rest), Vasodilator
• Increased glandular secretion

Sympathetic (from sympathetic chain, T1–T5):
• Bronchodilation (relaxation of smooth muscle – more air can enter during fight or flight). Vasoconstrictor
• Decreased secretions.

Visceral sensory fibers:
• Travel with vagus and sympathetic pathways.
• Mediate reflexes and pain sensation.

Superior - Houses great vessels (aorta, brachiocephalic artery, common carotid artery, subcalvian artery)

Middle - Houses the heart

Anterior - houses the thymus

Posterior - houses the sympathetic chain, azygous veinous system and the oesophagus

The heart sits in the fibrous pericardial sac and has two layers. The fibrous pericardium is the outermost layer, attaching to diaphragm and great vessels. The serous pericardium is the inner layer which can be divided into:
- Visceral (epicardium – covers heart surface)
- Parietal (lines fibrous pericardium)

The RCA runs in the coronary sulcus (space between right atrium and ventricle) and gives off two branches.

1) Marginal branch supplying RV

2) Posterior Interventricular / descending artery (PDA) supplying RV, LV and IV septum

The LCA is a short stem that branches into two arteries

1) The anterior interventricular artery (LAD) which supplies LV, Anterior septum and the apex of the heart

2) Circumflex artery which drains into coronary sulcus and supplies blood to LA + LV. This will bifrucate into left marginala arteries on the posterior heart

Great cardiac vein – Runs with LAD artery

Middle cardiac vein – runs with posterior interventricular artery (PDA)

Small cardiac vein – runs with RCA in coronary sulcus

Posterior cardiac vein – drains the posterior left ventricle

ALL DRAIN INTO Coronary sinus – A large venous channel in the posterior coronary sulcus that drains into the right atrium just medial to the IVC. It serves as the largest cardiac vein collecting deoxygenated blood and emptying into the right atrium

• Parasympathetic (Vagus nerve, CN X):
o Decreases heart rate (negative chronotropy).
o Reduces force of contraction (negative inotropy, mainly atria).
o Constricts coronary arteries slightly.

• Sympathetic (T1–T5 spinal nerves → sympathetic chain → cardiac nerves):
o Increases heart rate.
o Increases force of contraction.
o Dilates coronary arteries.

• Cardiac Plexus (Parasympathetic and sympathetic): Network of autonomic fibers around aortic arch and coronary arteries → distributes innervation for the SA node

There are 9 regions of the abdomen which are divided by 2 vertical lines (midclavicular) and 2 horizontal lines (subcostal plane and transtubercular plane)

Right Hypochondrium | Epigastric | Left Hypochondrium
| |
Right Lumbar | Umbilical | Left lumbar
| |
Right Inguinal | Hypogastric | Left Inguinal

• Peritoneum: Serous membrane lining abdominal cavity. Thin and translucent
o Parietal peritoneum lines walls. Somatic innervation
o Visceral peritoneum covers organs. Visceral innervation

• Omenta: Specific fold of visceral peritoneum
o Greater omentum – large apron-like fold from greater curvature of stomach → covers intestines. Fat-rich, immune role.
o Lesser omentum – connects lesser curvature of stomach & proximal duodenum → liver.

• Mesenteries: Double layer of peritoneum that suspends intestines from posterior abdominal wall (carries vessels, nerves, lymph).

• Peritoneal (intraperitoneal): Suspended by mesentery, fully covered by visceral peritoneum. (Stomach, liver, spleen, jejunum, ileum, transverse & sigmoid colon).

• Retroperitoneal: Lie behind peritoneum, only anterior surface covered. (Kidneys, pancreas, duodenum [2nd–4th parts], ascending & descending colon, adrenal glands)

• Parasympathetic (Vagus nerve, CN X):
o Increases motility (peristalsis). Smooth muscle contraction
o Increases secretion of gastric glands and production of acid (gastric emptying)

• Sympathetic (via celiac plexus, greater splanchnic nerves):
o Decreases motility & secretion (Inhibits peristalsis)
o Constricts blood vessels (vasoconstriction)

• Enteric nervous system: Local control via myenteric & submucosal plexuses

• Duodenum – first, C-shaped part; receives bile and pancreatic enzymes.
• Jejunum – middle portion; major site for absorption.
• Ileum – distal portion; absorbs bile salts and vitamin B₁₂.

Responsible for digestion and absorption of nutrients passing through the GI tract.

1. Superior (1st part): Intraperitoneal for ~5 cm then becomes retroperitoneal.
2. Descending (2nd part): Retroperitoneal; receives bile duct and pancreatic duct at the major duodenal papilla.
3. Horizontal (3rd part): Retroperitoneal; crosses anterior to the aorta and inferior vena cava.
4. Ascending (4th part): Retroperitoneal; ascends to duodenojejunal flexure (suspended by ligament of Treitz).

The superior mesenteric artery (SMA) supplies the small intestine. However the SMA forms a series of interconnected arterial arcades within the mesentery. Projecting from these arcades are numberous vasa recta (straight vessels) which arise to supply blood directly to the small intestine.

The jejunum is richer in arcades and vasa recta, giving it a more intense red colour

1. Caecum: Blind pouch below ileocecal valve; houses appendix.
2. Ascending colon: Retroperitoneal; extends to hepatic flexure.
3. Transverse colon: Intraperitoneal; from hepatic to splenic flexure.
4. Descending colon: Retroperitoneal; from splenic flexure to sigmoid.
5. Sigmoid colon: Intraperitoneal; leads into rectum.
6. Rectum

Haustra - Sacculations or pocuhes formed by tonic (constant) contractions of taenia coli. (The rounded shape of the large intestine)

Taenia Coli - three bands of longtitudinal smooth muscle which merge at the rectum (these contract to form those pocuhes)

Hepatic Flexure is the right colic flexure between the ascending and transverse colon

Splenic flexure is the left colic flexure between the transverse and descending colon

SMA providing blood to the cecum, ascending colon, and the proximal part of the transverse colon, while the IMA supplies the rest eg; transverse, descending and sigmoid colon to rectum

Parasympathetic: Cranial and Sacral outflow
• Vagus nerve (CN X) – supplies foregut & midgut (to ~2/3 transverse colon).
• Pelvic splanchnic nerves (S2–S4) – supply hindgut (distal colon & rectum).
• Function: ↑ Motility & secretion, ↑ glandular secretions, relaxation of sphincters.

Sympathetic: Thoracic and Lumbar outflow – Celiac and SMN / IMN
• From thoracic & lumbar splanchnic nerves via prevertebral ganglia (celiac, superior & inferior mesenteric).
• Function: ↓ Motility, ↓ absorption + secretion, ↓ glandular secretions, constrict vessels, close/contraction of sphincters.

Enteric Nervous System (ENS)
• Intrinsic network controlling GIT independently, known as the ‘little brain’. Made of 100 million neurons.

• Two plexuses:
o Myenteric (Auerbach’s) plexus – between muscle layers throughout GIT from oesophagus to rectum; regulates motility and motor aspects of gut function.

o Submucosal (Meissner’s) plexus – in submucosa in small and large intestine; regulates secretion and blood flow.

The rectum is just the continuation of the sigmoid colon as it passes through the pelvic floor to from the anus. The main muscle is puborectalis which forms a sling around the anorectal joint.

There are two sphincters - Internal and External anal sphincters
Internal anal sphincter is autonomic smooth muscle while the external anal sphincter is skeletal muscle that is voluntarily controlled via the pudendal nerve

The liver lays in the right hypochondriac and epigastric regions with a small portion extending into the left hypochondriac region. It sits just below the diaphragm deep to ribs 7-11 and is largely protected by the rib cage.

The Liver has two surfaces a diaphragmatic and visceral surface

Ligaments of the liver are folds of peritoneum anchoring the liver in position. The main ligament is the falciform ligament connecting the anterior liver to the anterior abdominal wall and diaphragm

The lesser omentum is another ligament-like structure connecting the liver to the stomach and duodenum

Anatomically, the liver has four lobes:
• Right lobe – largest; occupies most of right hypochondrium.
• Left lobe – smaller; lies in epigastric and left hypochondrium.
• Caudate lobe – on posterior surface, near IVC.
• Quadrate lobe – on inferior surface, between gallbladder and ligamentum teres.

Functionally, the liver is divided into right and left lobes by the middle hepatic vein and plane of the gallbladder fossa to the IVC, corresponding to the distribution of the hepatic arteries and bile ducts.

Porta hepatis is a short, deep transverse fissure that lies between caudate and quadrate lobes. It is known as the 'doorway to the liver' as it transmits the structures of the portal triad

The portal triad includes:
- Hepatic artery
- Portal vein
- Bile duct
- Nerves and Lymphatics

Lobules are the functional units of the liver and are hexagonal in shape.

Blood flow:
1. Blood enters via hepatic artery and portal vein at porta hepatis.
2. Both mix in hepatic sinusoids (capillary-like channels) within liver lobules.
3. Exchange occurs with hepatocytes → detoxification, metabolism, storage.
4. Blood collects in central veins of each lobule.
5. Central veins → hepatic veins → inferior vena cava.

1. Hepatocytes secrete bile into bile canaliculi (small channels between cells).
2. Canaliculi drain into bile ducts (in portal triad at periphery of lobule).
3. Bile ducts merge into right and left hepatic ducts → common hepatic duct.
4. Common hepatic duct joins with the cystic duct from the gallbladder to form the the common bile duct which then joins the main pancreatic duct at the ampulla of vater
4. Bile then flows to gallbladder (via cystic duct) or to duodenum (via sphincter of Oddi)

Blood supply is from the common hepatic artery - a branch from the celiac trunk
- The common hepatic artery then transitions into the proper hepatic artery
- The hepatic artery proper bifurcates into the left and right hepatic arteries

The portal vein also provides nutrient rich blood from digestive organs via the superior and mesenteric veins and splenic veins

Duct system:
• Cystic duct: Connects gallbladder neck to common hepatic duct.
• Common bile duct: Union of cystic and common hepatic ducts; runs posterior to first part of duodenum and head of pancreas to reach duodenum.

Blood supply:
• Arterial: Cystic artery (branch of right hepatic artery).
• Venous: Cystic veins → drain directly into liver or portal vein.

The pancreas is located in the epigastric region and left hypochondrium region of the abdomen across the posterior abdominal wall at L1-L2. The pancreas' head is nestled in the C-shaped curve of the duodenum and its body and tail extends horizontally to the spleen.

The main pancreatic duct or the Duct of Wirsung joins the common bile duct at the ampulla of Vater then proceeding to run the entire length of the pancreas. Pancreatic juice and bile flow through this duct and its release into the duodenum is controlled by the sphincter of Oddi at the major duodenal papilla.

The Accessory duct or Duct of Santorini drains the upper part of the head and empties into the duodenum via the minor duodenal papilla

Blood supply is complex with some arterial supply branching off the celiac trunk and others from the superior mesenteric artery.
- The head is supplied by the SMA
- The body and tail is supplied by pancreatic branches of the splenic artery (one of the three main branches off the celiac trunk)

The exocrine function involves Acini and Duct cells with the role of releasing digestive juice into ducts, which eventually make its way into the duodenum.

• Acinar cells → secrete digestive enzymes (pancreatic amylase, lipase, proteases, nucleases, trypsin, chymotrypsin).

• Duct cells → secrete bicarbonate-rich fluid (neutralizes acidic chyme by raisng pH).

The Endocrine Pancreas (Islets of Langerhans) – release hormones into blood
• α (alpha) cells (17%) → Glucagon → raises blood glucose (stimulates glycogenolysis, gluconeogenesis, lipolysis).
• β (beta) cells (70%) → Insulin → lowers blood glucose (stimulates glucose uptake, glycogenesis, lipogenesis, protein synthesis).
• δ (delta) cells (7%) → Somatostatin → inhibits insulin + glucagon, slows digestion (paracrine control).
• PP (F) cells (6%) → Pancreatic polypeptide → regulates exocrine secretion + bile release, inhibits gallbladder contraction and somatostatin

The ligaments of the spleen are similar to that of the liver, in that they are just folds of the peritoneum in which anchor the spleen to other structures.

Gastrosplenic ligament connects the spleen to the stomach (greater curvature of peritoneum)

Splenorenal ligament connects the spleen to the left kidney

• Renal cortex:
o Outer granular layer beneath the capsule.
o Contains renal corpuscles (glomeruli + Bowman's capsule).
o Extends inward between pyramids as renal columns.

• Renal medulla:
o Inner, striated layer made of renal pyramids.
o Each pyramid’s apex = renal papilla, which projects into a minor calyx.

• Minor calyces: Collect urine from each papilla.

• Major calyces: Formed by fusion of 2–3 minor calyces.

• Renal pelvis: Funnel-shaped cavity continuous with the ureter at the hilum.

The kidneys recieve major blood supply with approximately 20% of cardiac output at rest going to kidneys. The kidneys is supplied by the right and left renal arteries which divide into:
- Segmental arteries
- Interlobar arteries (run between pyramids)
- Arcuate arteries (arch over pyramid base)
- Interlobular arteries which turn to
- Afferent arterioles which lead into the glomerulus

Renal veins drain into the Inferior Vena Cava (IVC)

Urine production occurs via the nephron (the functional unit of the kidney with approximately 1 million per kidney).

1. Renal corpuscle (in cortex):
o Glomerulus (capillary tuft) + Bowman’s capsule
o Function: Filtration of blood plasma → filtrate (primitive urine)

2. Proximal convoluted tubule (PCT):
o Reabsorbs ~65% of filtrate (water, ions, glucose, amino acids)
o Function: Selective reabsorption

3. Loop of Henle:
o Descending limb → water reabsorption
o Ascending limb → Na⁺, Cl⁻ reabsorption
o Function: Creates osmotic gradient (concentrates urine)

4. Distal convoluted tubule (DCT):
o Regulates salt and pH
o Responds to aldosterone

5. Collecting duct:
o Adjusts water reabsorption under ADH (antidiuretic hormone)
o Function: Final concentration and transport of urine

Apex – the points anteriorly attached to anterior abdominal wall by the median umbilical ligament

Base (fundus/posterior) – orientated posteriorly it is related to the rectum or vagina

Body – main central portion

Neck – inferior region which leads into urethra by puboprostatic ligaments in females, or pub vesical ligaments

Trigone – smooth triangular area on internal surface between ureteric openings and internal urethral orifice.

The bladder's base (fundus) and neck is anchored by several ligaments with the most important being:
- Puboprostatic ligaments in Males connecting the prostate to the pubic bone
- Pubovesical ligaments in Females supporting the bladder and urethra

The main muscle of the bladder is the detrusor muscle with is a smooth mucle layer forming the bladder wall. This can stretch to store urine and contracts to expel it. Other muscles include the internal (involuntary) and external (voluntary) urethral sphincters

The bladder is supplied by:
• The superior vesical arteries (from the umbilical artery to the internal iliac)

• The inferior vesical arteries (from the internal iliac artery)

Abdominal aorta → Common iliac → Internal Iliac → Umbilical artery → Superior Vesical artery
OR
Abdominal aorta → Common iliac → Internal Iliac → Inferior vesical artery

The vesical venous plexus drains into the internal iliac veins which eventually makes its way to the inferior vena cava.

In males, bladder venous drainage recieves contribtuons from the prostatic venous plexus aswell

The Bladder, being a visceral organ, is controlled by the ANS.

Parasympathetic innervation
• Pelvic splanchnic nerves (S2-S4)
• Act to contract detrusor muscles and relax internal sphincter to promote urination

Sympathetic Innervation
• Hypogastric plexus (T11-S2)
• Relaxes detrusor and contracts internal sphincter to promote urine storage

Micturition is the process of emptying the urinary bladder, also known as pissing. In order for micturition to occur, three things must occur simultaenously.
1) The detrusor muscle must contract
2) The internal sphincter must relax or open
3) The external urethral sphincter must relax or open

Therefore the process is as follows:
1) The urinary bladder fills, stretching the bladder wall
2) Afferent impulses from stretch receptors send information to increase parasympathetic activity and inhibit sympathetic activity.
3) The detrusor muscle contracts and the internal sphincter opens (relaxes)
4) Urination or micturition occurs.

The pelvic skeleton is formed by four bones: Two hip bones, a sacrum and and coccyx

Each hip bone is formed by the fusion of three bones to form the innominate bone
• Ilium – superior, fan-shaped portion
• Ischium – posteroinferior portion (forms the “sit bone”)
• Pubis – anteroinferior portion

These three bones meet at the acetabulum, the deep socket that articulates with the femoral head

• Sacroiliac joint
o Between sacrum and ilium.
o Type: Synovial (anterior) + fibrous (posterior).
o Function: Transfer weight from upper body to lower limbs.

• Pubic symphasis
o Between pubic bodies.
o Type: Secondary cartilaginous joint (fibrocartilaginous disc).
o Allows slight movement (important in childbirth).

• Lumbosacral joint
o Between L5 and S1

• Sacrococcygeal joint
o Between sacrum and coccyx (slightly movable).

• Anterior and posterior sacroiliac ligaments - strengthen the SI joint

• Sacrospinous ligament - from the sacrum to the ischial spine forming the greater sciatic foramen with the sacrotuberous

• Sacrotuberous ligament - from the sacrum to the ischial tuberosity to form the greater and lesser sciatic foramen

The main muscles of the pelvic diaphragm
The pelvic diaphragm (floor) supports the pelvic organs and helps maintain continence.
Main Muscles:
1. Levator ani group: From closest to vaginal canal to the coccygeus
o Puborectalis (forms a sling around the anorectal junction
o Pubococcygeus
o Iliococcygeus

2. Coccygeus (ischiococcygeus):
o From ischial spine to sacrum/coccyx.
o Supports pelvic floor, pulls coccyx forward after defecation.

Innervation:
• Pudendal nerve (S2–S4) and direct branches of S3–S4.

The pelvis recives nerves from two main plexuses: The lumbrosacral plexus and the coccygeal plexus

Lumbosacral Plexus
• Sciatic nerve (L4–S3): exits via greater sciatic foramen below piriformis.
• Pudendal nerve (S2–S4): exits pelvis via greater sciatic foramen, re-enters via lesser sciatic foramen → supplies perineum and external genitalia (motor and sensory)

From the Coccygeal Plexus:
• Coccygeal Nerve: Nerve to levator ani and external anal sphincter

Perineum is the diamond-shaped area of skin and tissue between the anus and the genitals. In males, it is the area between the anus and the scrotum, and in females, it is between the anus and the vulva.

It can be divided into two triangles by an imaginary line between the ischial tuberosities
• Urogenital triangle (anterior)
• Anal triangle (posterior)

The perineum has a deep and superficial layer. The deep layer houses:
• The pelvic diaphragm
• The perineal membrane (tough fibrous sheet seperating deep and superficial perineal pouches, also providing attachment for erectile tissue and external genitalia muscles.
• The deep perineal pouch (Above the perineal membrane which contains the external urethral sphincter, the bulbourethral glands in males and part of the urethra and vagina in females)

The superificial layer features the superficial perineal pouch situated below the perineal membrane housing:
o Ischiocavernosus (lock in the rigidity of an erection)
o Bulbospongiosus (help expel semen)
o Superficial transverse perineal muscle

• Structures:
o Erectile tissues:
Males: Crura of penis form the → corpora cavernosa; bulb of penis → corpus spongiosum (middle part)

Females: Clitoris, bulbospongiosis, ishiocavernosis

The internal Iliac artery is the primary blood supply to pelvic organs, perineum and gluteal region. The internal iliac, as we have seen, branches into many smaller arteries to supply different areas.
• Superior vesical arteries - Bladder
• Inferior vesical artery - Bladder, prostate

Located below the bladder, this small chest-nut sized organ is to produce a fluid (prostatic fluid) that nourishes and transports sperm, which mixes with sperm to form semen.

Scrotum – the pouch of skin housing the testes epididymides, and distal spermatic cords

The testis (singular form) is the site of spermatogenesis and is covered by tunica albuginea (dense connective tissue capsule

The epididymis is a long-coiled cut posterior to the testis that collects, matures and stores sperm. It connects the testicles to the vas deferens which transports sperm out of the body.

Tunica albuginea is the dense fibrous inner layer that directly covers the testicles itself while the tunica vaginalis is the outer-double layered serous membrane (parietal and visceral layers) that encloses the testes.

The tunica vaginalis is the continuation of the peritoneum

After these layers of tunic, the scrotum is covered by different types of spermatic fascia until it is finally enclosed by the skin and dartos (smooth muscle layer).

The penis is three cylinders of erectile tissue - two corpora cavernosum and one corpus spongiosum.

Corpora cavernosum - engorges or swells with blood during erection

Corpus spongiousm - situs underneath, supporting urethral collapse during erection

The three perineum muscles we focus one are:

Ischiocavernosus – compresses crus and helps maintain and stabilise erection

Bulbospongiosus – helps empty urethra after urination, compresses erectile tissue, contraction during ejaculation to help expel semen

Transverse perineal muscle – stabilises the perineal body

Thankfully, many of the arteries in the male reproductive tract are named based on their location eg; posterior scrotal, deep artery of penis etc. However we must know these major arteries or branches such as the internal and external pudendal artery.

Testes – testicular arteries, a branch directly from the abdominal aorta at L2

Epididymis + Ductus deferens – Artery to ductus deferens from inferior vesical artery

Pudendal artery is a branch off the internal iliac artery supplying many male reproductive structures

The male reproductive system is mainly innervated by the ANS system with the pudendal nerve providing some motor control and innervation to the external genitalia, eg; external urethral and anal sphincters.

The Mnemonic we use is 'Point and Shoot'.
- Parasymathetic innervation or point uses pelvic splanchnic nerves (S2-S4) to promote vasodilation and ultimately erection (which points)

- Sympathetic innervation or shoot uses the hypogastric plexus to promote the closure of the internal sphincter (so urine doesnt mix with semen, or semen returns to the bladder) and cause ejaculation (which shoots semen)

The uterus is held in place by fibromuscular ligaments and the pelvic diaphragm. The main ligaments supporting the Uterus include:

• Broad Ligamet (Large double fold of peritoneum extending from the uterus to lateral pelvic walls to provide 'sling-like' support)

• Round Ligament (extending from uterine horns through the inguinal canal to the labia majora)

• Uterosacral Ligament (extending from cervix to sacrum posteriorly which maintains uterine position and prevents prolapse)

• Transverse cervical (cardinal) Ligament (extends from cervix to lateral pelvic walls)

• Pubocervical (from cervix to the posterior surface of the pubic symphasis)

The broad ligament is the double fold sheet of peritoneum that is sandwiched together oon both sides of the uterus. The broad ligament is composed of three parts:

Mesometrium
- The largest portion that extends from the lateral uterus to pelvic wall containing the uterine vessels.

Mesosalpinx
- Superior portion enclosing the uterine tube

Mesovarium
- Posterior portion attaching ovary to broad ligament

Within the broad ligament lays:
- The uterus (a pear shaped organ between the bladder and rectum)
- The uterine or fallopian tubes (transports oocytes from ovaries to uterus)
- Ovaries (site of oogenesis and hormone secretion)
- Round ligament (extend from uterine horns, through inguinal canal to labia majora)

Again, as with the male reproductive system, arteries tend to be named by where they are located or what they supply. Nonetheless, we must know that its the internal iliac artery that splits into anterior and posterior trunks whereby the anterior trunk houses many of the important arteries.
- Vaginal artery
- Uterine artery
- Internal pudendal artery

The abdomianl aorta also contributes by supplying the ovarian artery which travels with the suspensory ligament to supply the ovary and uterine tube. This artery will enlrage during pregnancy

For the external perineum of the female reproductive tract we should know and be able to identify
- Labia majora (outer fold of skin)
- Labia minora (inner thin folds)
- Clitoris (erectile tissue)
- Vagina (the fibromuscular tube that extends from cervix to vestibule)
- Mons pubis (the fat pad above pubic symphasis)

The female reproductive system recieves somatic sensation and motor innervation from the pudendal nerve. This efferent nerve provides excitatory innervation to bulbocavernosus, ischiocavernosus and the pelvic diaphragm muscles during orgasm

The ANS system also plays a role similar to the male reproductive system:
Sympathetic innervation from the hypogastric plexus caused vasoconstriction, uterine contraction an orgasm response and a loss of erection.

Parasympathetic innervation from the pelvic splanchnic nerves caused vasodilation of clitoral arteries, the relaxation of smooth muscles and expansion of sinusoidal spaces to cause engorgement and lubrication

Ejaculation is one of the rare cases where we see the sympathetic and parasympathetic systems working together in the same organ

The lymphatic system is responsible for:
• returning interstitial fluid (plasma leaks from capillaries) back into the venous system.
• transporting lipids and lipid soluble vitamins from the small intestine via lacteals
• filtering lymph through lymph nodes to trap pathogens and debris
• promote immune response surveillance via lymphocytes and macrophages in lymphoid tissue

Lymph - clear fluid similar to plasma but low in proteins contianing lymphocytes and waste products

Lymphatic vessels - thin-walled channels with valves to transport lymph

Lymph nodes - small bean shaped filters that remve pathogens and are located aling lymphatic vessels

The lymphatic system lacks an organ like the heart to act as a pump so in its normal conditions lymphatic vessels are low pressure channels with mechanisms similar to venous return. The general pathway of lymph is as follows:
• Intersitial fluid enters lymphatic capillaries
• Capillaries move this lymph to lymphatic vessels
• These afferent vessels move past lymph nodes which filter the lymph and inititate immune responses if needed.
• Now Efferent, these vessels carry lymph to larger lymph trunks to drain into lymphatic ducts like the thoracic duct

Lymph from the upper right side of the body (right upper limb, head, neck, thorax etc) drains into the right subclavian vein via the right lymphatic duct which is situated between the internal jugular vein and right subclavian

Lymph from the left side and rest of the body (both lower limbs, abdomen etc) drains into the left subclavian vein via the thoracic duct which similarly is situated between the left internal jugular vein and left subclavian

Lymphoid tissue houses and provides a proliferation site for lymphocytes and an ideal vantage and surveillance point for lymphocytea and macrophages in immune response. The primary lymphoid tissue is the thymus where T cells grow and mature and Bone marrow where B cells mature.

Other lymphoid tissue seen in the body includes:
Spleen – filters blood, recycles RBCs and mounts immune response
Tonsils – protect upper respiratory and digestive tracts
Peyer’s Patches (Ileum) – Monitor intestinal bacteria

The glymphatic system is a waste clearance pathway in the CNS much like the bodies lymphatic system. It is glial-dependant using CSF to flush out metabolic waste from the brain eg; proteins and toxic solutes.

This process is far more active during sleep, as the brain increases its volume of intersitial fluid to enhance waste removal.

All waste drains into meningeal lymphatic vessels which connect to cervical lymph nodes.