Biomedical Science - Semester 1

Chemical, cellular, tissue, organ, organ system, organism

Digestive system - breaks down food so we can use it for energy
Endocrine system - Regulates bodily functions such as metabolism, growth, reproduction etc
Nervous system - Transmits nerve impulses around the body, carrying instructions and information
Respiratory system - Responsible for breathing and the exchange of oxygen and carbon dioxide with the external environment
Reproductive system - Responsbile for the production of gametes for procreation
Integymentary system - protects the body from the external environemnt, eg; thermoregulation
Cardiovascular system - transports blood and oxygen to muscles and cells around the body
Muscular system - Responsible for moving the body
Skeletal system - Responsible for structure, protection and voluntary movement
Lymphatic system - responsible for transporting lymph throughout the body
Urinary system - responsible for the removal of waste and filtering of blood

Homeostasis is the maintaining of a relatively stable internal environment regardless of changes in the external environment

1. Detecting a change: Receptors (sensory cells) detect a change in a variable above or below a set point in the internal environment. This change is called the stimulus

2. Counteracting a change: This is the change that will counteract the stimulus, returning the internal state to its set point. This is brought about by effectors, isntructed by the control centre

The negative feedback mechanism is the process by which the control centre recieves information from receptors, signalling a deviation in an internal set point. The control centre sends information (nerves or hormones) to effectors to carry out a process to reverse this effect. Once the set point is reached, signals are sent back to the control centre by receptors to stop the process, which then results in the control centre instructing the effectors to stop the process, known as the negative feedback mechanism.

- Thermoreceptors in the skin detect a chnage in temperature above or below the set point of 37 degrees
- If body temperature is too high, information is sent to the front of the hypothalums (the heat loss centre) whereas if its too low information is sent to the back of the hypothalamus (heat gain centre).

- Instructions are sent via nerves to effectos to carry out responses to return temperature back to normal

The Back of the hypothalamus can instruct the body to generate / trap heat by:
- Shivering - rapid muscular contractions to generate more heat
- Piloerection - hair particles stand on end to trap heat
- Vasocontriction - blood vessesl contrict and move away from surface to reduce heat loss via radiation
- Release of TSH to increase the amount of thyroxin, increasing metabolism and in-turn heat.

The front of the hypothalamus can instruct the body too remove heat by:
- Sweating - heat loss via evaporation
- Reduction in thyroxin produced
- Vasodilation - blood vessles dilate and are brought closer to the surface to increase heat loss by radiation

- Blood glucose has a set value of 90mg / 100ml and if blood glucose levels are too high insulin secreting beta cells of the pancreas (receptor) are released or glucagon-releasing alpha cells of the pancreas are released if blood glucose is too low.
- Once 90mg / 100ml is reached, the pancreas is instructed to stop releasing alpha and beta cells

Insulin secreting beta cells release insulin into the blood stream which encourage more cells to take up glucose, lowering blood glucose to a normal range. Excess glucose is stored in the liver as glycogen

Glucagon releasing alpha cells break down glycogen stores of the liver into glucose, releasing it into the bloodstream to increase blood glucose concentration.

Atoms are basic building blocks of all matter and are made up of three important subatomic particles.
- Neutrons (neutral charge found within the nucleus)
- Protons (positivvely charged found within the nucleus)
- Electrons (negative charge,orbiting the nucleus)

- Covalent bonds
- Ionic bonds
- Hydrogen bonds

Covalent Bonds occur when two atoms share electrons to create, strong stable molecules. The shared electrons allow each atom to reach a stable outer shell (usually 8 electrons, known as the octet rule). Covalent bonds are strong bonds that can be stronger than Ionic.

Ioninc bonds occur when an atom donates or recieves a valence electron from another atom due to electrostatic attraction (the attarction between oppositely charged ions - cation and anions) and a large difference in electronegativity. This creates a positively charged cation and negatively charged anion, together resulting in a polar bond.

An anion may be defined as an atom or molecule that is negatively charged. A cation may be defined as an atom or molecule that is positively charged.

Essentially, a molecule that looses electrons (electron donors) becomes a cation and possess a net positive charge. Similarly, a molecule that gains electrons (electron acceptors) becomes a anion and possesses a net negative charge.

An electrical attraction between anions and cations forms an ionic bond

Polar Covalent bonds are charachteristic of an unequal sharing of valence electrons, creating a slight positive charge (+ve) on one side of the molecule due to one atom having a higher electronegativity. EG; H20 (Water)

Nonpolar bonds are charachterisitc of an equal sharing of valence electrons, creating a more stable, stronger bond. eg; 02 (oxygen)

Ionic bonds involve a complete transfer of electrons from a metal atom (which becomes a positively charged cation) to a nonmetal atom (which becomes a negatively charged anion) causing an unequal sharing of electrons due to the electronegativity of one atom being significantly stronger than the other.

EG; Sodium Chloride or table salt is made as sodium (Na) looses its electron to become positivel charged (Na+) and Chlorine (Cl) recieves an electron to become negatively charged (Cl-)

a measure of an atom's ability to attract shared electrons to itself. Key to understanding how polar bonds / ionic bonds are created (unequal sharing of electrons on outer shell)

Polar molecules have charged ends due to unequal sharing of electrons (eg; ionic bonds and a strong electronegativity). These molecules posses hydrophilic properties

Nonpolar molecules lack charged ends due to a more stable share of electrons and ar egenerall stronger than polar bonds. These molecules possess hydrophobic properties

Carbon is the backbone of all living organisms as it is a primary element in all molecules that make up our body. This is because carbon has 6 protons, electrons and neutrons. Carbon has four valence electrons (electrons on the outer shell) allowing it to form four seperate covalent bonds to fulfill the octet rule and form more complex, longer chains / molecules.

Carbon is a key feature to the four macromolecules contributing to human function and structure
1) Carbohydrates such as sugars and starches fare made up of carbon, hydrogen and oxygen in the ration 1:2:1, for example C₆H₁₂O₆ for glucose
2) Lipids such as fats and oils are made of long hydrocarbon chains (nonpolar covalent bond)
3) Proteins made up of amino acids feature carbon as a key element
4) Nucleic acid such as DNA and RNA requires carbon. For example a nucleotide is made up of a pentose sugar backbone (involving carbon), a phosphate group and a nitrogenous base (also involving carbon)

A phospholipid bilayer is a structure made of two layers of phospholipids that form the basis of cell membranes.
• Phospholipids are amphipathic molecules, meaning they have both hydrophilic and hydrophobic parts.
• The hydrophilic heads (polar) face the water, while the hydrophobic tails (non polar) are shielded from the water.
• The bilayer forms a stable barrier between two aqueous compartments, such as the inside and outside of a cell.
• The bilayer is selectively permeable, allowing some molecules to pass through while blocking others.

Hydrophobic means 'water repelling' and refers to substances that do not dissolve in or interact with water, eg; All non-polar molecules such as the tails of a phospholipid

Hydrophilic means 'water loving' and refers to substances that readily dissolve in or interact with water eg; All polar molecules such as Phospholipid heads

Made of carbon, hydrogen and oxygen and include monosaccharides (simple sugars like glucose), disaccharides (joining of two monosaccharides) and polysaccharides (the combining of mono or disaccharides). They provide energy, store energy (glycogen in animals, starch in plants), and contribute to cell structure

Lipids are made of glycerol and fatty acids responsible for storing energy, insulation, the protection of vital organs and the formation of cell membranes

Triglyceride is made up of 1 glycerol and 3 fatty acids

Metabolsim refers to all chemical reactions occuring in cells and tissues of our body at any given time to provide energy to maintain homeostasis, growth and maintenance. Metabolism often involves the use of exergonic reactions (catabolism) to provide energy to drive an endergonic reaction (anabolism)

1. Catabolsim (exergonic reactions - a reaction that releases free energy in the process of the reaction)

2. Anabolism (endergonic - a reaction that requires energy to be absorbed in order for it to take place)

Catabolism or 'breakdown reactions' involves larger molecules being broken down into smaller, more simpler molecules, releasing energy when bonds are broken.

Catabolsim usually involves an oxidation or hydrolysis reaction ⭐

For example cellular respiration as Glucose is broken down into ATP via hydrolysis as water is consumed

Anabolism or 'building reactions' involve the formation of larger, more complex molecules from simpler molecules, requiring energy in the process.

Anabolism usually involves a reduction or condensation reaction ⭐

For example the synthesis of proteins from amino acids or photosynthesis as water is produced via condensation

A dehydration reaction (also called condensation reaction) occurs when monomers combine to form larger molecules (polymers) by removing a water molecule (H₂O).
- Formation of polysaccharides from carbohydrates
- Formation of Proteins from peptide bonds
- Formation of trigylcerides from glycerol and fatty acids

A Monomer is a molecule that can react together with other monomer molecules to form a larger polymer chain or three-dimensional network in a process called polymerization

A hydrolysis reaction occurs when larger molecules (polymers) are broken down into smaller monomers by adding water (H₂O). The process involves the addition of a water molecule where the hydrogen (H) of the water molecule attaches to one part of the molecule, whilst the hydroxyl group (-OH) bonds to another, breaking the bond
- Breakdown of polysaccahrides
- Breakdwon of proteins
- Breakdown of triglycerides
- Breakdown of Glucose into ATP

Proteins are made up of amino acids and are the building blocks for life, eg; skin, muscles, hormones, enzymes. They are made through the processes of polypeptide synthesis, involving transcription (the process whereby DNA is transcribed into mRNA) and translation (the process where by mRNA is translated into polypeptide chains).

S - Structure (collagen)
H - Hormones (Insulin)
I - Immunity (antibodies - immunoglobins)
T - Transport (Hemoglobin)
S - Sensation (opsins - family of light sensitive proteins)
M - Movement (actin and myosin for muscular contractions)
E - Enzymes (amylase, protease - digestive enzymes)

- A cell membrane, formed by a phospholipid bilayer
- Cytoplasm (gel-like fluid inside cells and everything outside the nucleus)
- Nucleus
- Cytosol (the aqueous component of the cytoplasm)
- Intracellular fluid, consisting of interstitial fluid (75%) and plasma (25%)
- Membranous organelles (have their own plasma membrane) like mitochondria
- Non-membranous organelles (no plasma membrane) like ribosomes

- A phospholipid bilayer which will control what enters and exits the cell through polar (hydrophilic heads) and non-polar (hydrophobic tails), eg; water
- Proteins such as peripheral proteins and integral proteins
- Integral proteins are part of the membrane structure and can be divided into multiple functions, eg; a channel protein (a pore for which ions can travel through) and carrier / transporter proteins (carry substances across the cell membrane like amino acids)

- Cell membranes provide structure for the cell, clearly defining the internal and external contents of the cell, supporting the cytoskeleton (internal protein framework, providing strength and flexibility)
- Cell membranes are selectively permeable, meaning they can control what enters and exits the cell, thus keeping essential nutrients and removing waste products.
- Cell membranes also facilitate the movement of substances across its barrier through mechanisms like diffusion, osmosis and active transport (transport proteins)

The cytoskeleton is responsible for maintaining cell shape and structure, organising internal components, enabling movement and facillitating cell division

Microfilaments such as actin and myosin which provide mechanical support and generate movement

Intermediate filaments which strengthen and maintain cell shape whilst stabilising the position of organelles and the cell

Microtubules which are hollow tubes of tubulin which help determine cell shape and function in the movement of organelles such as chromosome during cell division

Centrosomes are non-membrane bound organelles known as microtubule organising centres (MTOC). These form the central part of chromosomes where mitotic spindle fibres extend from in cell division

Centrioles are located within centrosome and are paired barrel-shapped organelles playing a key role in organising microtubules in which form the cells cytoskeleton

The nucleus is an essential organelle found in most eukaryotic cells serving as a control centre, overseeing cellular activities and housing genetic material

It features a:
- Nuclear envelope which is a double membrane structure the surronds the nucleus, seperating it from the cytoplasm.
- Chromatin within the envelope which condenses to form chromosomes in cell division
- Nucleolus, a dense spherical structure inside the nucleus responsible for producing ribosomal RNA
- Nucleoplasm, a gel like substance filling the nucleus and providing a medium

Stores the cell's DNA
Controls gene expression through trasncription of DNA into RNA
Ribosome production essential for protein synthesis
Ensures cell division accuracy (replication and segregation of genetic material)

Passive processes are those that do not require ATP or cellular energy to perfrorm but rather rely on a conenctration gradient to transport substances across the cell membrane

Active processes are those that require cellular energy (ATP) to move substances across the cell membrane, against the concentration gradient.

Simple diffusion - movement of molecules from an area of higher concentration to an area of lower concentration

Facillitated diffusion - the use of specific proteins (protein carrier and channels) to transport substances across the membrane that couldn't originally get across the hydrophobic pores of the cell membrane, eg; too large.

Osmosis - the movement of water molecules from an area of low solute concentration / higher water conenctration to an area of high solute concentration / lower water concentration. Water moves from hypotonic to hypertonic

(REMEMBER a higher solute concentration means less water to salt ratio and thus a low solute conenctration means more water to salt)

Primary active transport (PAT) - involves the direct use of ATP to transport substances against the concentration gradient

Secondary active transport - Uses the energy stored in the electrochemical gradient of one substance (created by PAT) to drive the movement of another susbtance. Uses antiports to set up the gradient by transporting stored energy to the outside of the cell (PAT), then a symport uses the stored energy to bypass the membrane and make its way into the cell.

Vesciles -

Transcription - the process whereby messenger RNA is formed by a single DNA strand

1. The enzyme RNA polymerase binds to a sequence of DNA known as the promoter, where it begins to unwind the DNA molecule, breaking hydrogen bonds.
2. The sense or coding strand of DNA is used to form a complementray mRNA strand via complementary base pairing using freely found nucleotides (A-T C-G)
3. The sequence of the bases will be the same as the antisense or non-coding strand except Thymine will be replaced by Uracil
4. This mRNA strand will exit the nucleus via pores and make its way into the ctyoplasm where ribosomes are located

Translation - the process whereby messenger RNA is used to form polypeptide chains which join to form final product proteins

1. Ribosomes move along the mRNA strand, reading the codons of mRNA and attaching the corresponding tRNA molecules to it
2. These tRNA carrier molecules carry the anticodon (complementary bases to the codon of mRNA) at one end and the produced amino acid at the other
3. When mRNA and tRNA bind, the amino acid splices off via an enzyme and joins a growing polypeptide chain
4. Once this polypeptide chain is complete, it is processed in the cell where it may join and fold with two or more other polypeptide chains to form its final product protein

Incomplete dominance is where neither allele is dominant over the other, resulting in a blend of the two alleles, giving an intermediate appearance - Pink flowers

Co-dominance is where both alleles are expressed in the heterozygous offspring - Cows with brow and white fur / coats

Multifactorial dominance is where there are multiple alleles for that single trait and they are also heavily influenced by environmental factors - Cleft palate or skin colour, weight etc

X-linked dominance is where the genes on the X chromosome carries information other than determining the sex of the individual - male pattern baldness

Interphase - The cell replicates its DNA preparing it for cell division
Prophase - The chromosomes pair up and condense into there X-shaped structure while the membrane around the cell disolves away and the centrioles of the cell move to opposite poles
Metaphase - The chromosomes line up end to end along the equator of the cell whilst the mitotic spindle fibres extend from the centrioles on opposite poles of the cell
Anaphase - The contracting spindle fibres attached to the centromere of the homologous chromosomes pulling the sister chromatids apart to opposite sides of the cell
Telophase - A membrane forms around each complete set of chromosomes at both sides of the cell, cytokinesis simultenously occurs as the single cell pinches in the middle to form two genetically identical daughter cells each containing a full set of chromosomes within a nucleus

G0 Phase (the resting phase) - where some cells not involved in cell division such as muscle and nerve cells enter a non-dividing state known as G0
G1 Phase (Growth phase 1) - where the cell grows in size, synthesising organelles and proteins. Conditions in the internal environment are closely monitored in this stage to ensure if its suitable for DNA replication.
S Phase (synthesis phase) - DNA replication occurs as each chromosome is copied to synthesise identical sister chromatids
G2 Phase (Growth phase 2) - The cell checks DNA for errors and repairs any damage whilst also producing the final proteins and organelles needed for cell division

Mitosis is a single division producing two genetically identical diploid daughter cells for cell growth and repair

Meoisis is a reduction division involving two seperate cell divisions to produce 4 genetically unique haploid daughter cells (sex cells) f=to increase genetic variation in offspring

Metaphase & Anaphase in Mitosis = Chromosomes line up end to end on the equator of cell and sister chromatids are pulled apart by mitotic spindle fibres

Metaphase & Anaphase in Meoisis = Chromosomes line up next to eachother (Metaphase I) and whole chromosomes are pulled to oppsotie sides of the cell (Independant assortment - Anaphase I). Metaphase II and Anaphase II are similar to mitosis except the law of random segregation occurs to create 4 haploid gentically different daughter cells

Muscular tissue
Nervous tissue
Epithelial tissue
Connective tissue

In order to aggregate these cells into tissue types cells are required to be connected together. This is done through cell junctions. Cell junctions anchor cells, stabilising cell position and ultimately forming the epithelium structure.

A type of cell junction obstructing passage between cells and sealing them together via interlocking membrane proteins

A type of cell junction that allows small molecules to pass directly between adjacent cells through a channel via diffusion. This involves specialised proteins called connexons which interlock membranes and create this passageway

Junctions that join cells together, preventing seperation during contractile activity. Involves interlocking membrane proteins (cadherins) that form a layer of protein known as plaque, which connects it to the actin filaments (or microfilaments) of the cytoskeleton, serving as an adhesion 'belt' around the adjacent cell membranes

Desmosomes are the strongest cell junction in which provides resistance to mechanical forces and increases adhesion between cells. It uses desmosomal cadherins to anchor these tightly pakced cells to intermediate filaments of the cytoskeleton

Hemidesmosomes are half of the desmosome which rather than linking adjecant cells to one another, they anchor the cells to a base membrane. EG; the basal layer of the epidermis, relies on hemidesmosomes (that is, our skin)

In order to be effective, epithelial tissue must completely cover of line the parts of the body. Epithelial tissue
- Seperates and provides physical protection between biological compartments
- Provides sensation, controls permeability, influencing homeostasis
- Provides specialised secretion of cells

Cellularity - Comprised almost entirely of the same closely packed cells with some extracellular matricx
Polarity - Has an apical surface (exposed to the environment or cavity) and a basal surface (attached to a basement membrane, then to connective tissue)
Avascularity - Lacks blood vessels thus relying heavily on underlying tissue, such as connective tissue to provide nutrients to meet its demands
Innervated - Provides sensory input and output for regulation
Regenerative capabilities - Replace and repair lost or damaged tissue

Microvilli - small finger like projections that increase SA:V for absorbtion in the small intestine

Cilia - hair like projections that move substances across the surface of the respiratory tract

Squamos tissue is thin and flat with a large surface area, eg; alveoli of lungs

Cuboidal tissue is cubed-shaped tissue

Columnar tissue is tall and skinny

In addition to simple squamous, cuboidal and columnar epithelial tissue, the arrangement of layers determines its name.

Simple = a single layer
Stratified = layered (multiple layers) EG; Stratified squamous = epidermis or skin
Pseudostratified = appears to be layered (pseudostratified columnar is common)
Transitional = tissue that has elastic properties and is able to strech and return to a less relaxed position, Squamous when streched (flat) and cuboidal when relaxed

Glandular epithelium or glandular tissue is a specialised type of epithelial tissue that produces and secretes substances like hormones, enzymes and mucus, forming glands.

Exocrine glands release secretions into ducts which open onto the epithelial surface, for example sweat glands, salvivary glands and mammary glands

Endocrine glands secrete their products (eg hormones) directly into the bloodstream, for example thyroid glands, pituitary gland (hormones), adrenal glands (stress response)

Merocrine - most common type of secretion involving exocytosis to secrete waste without damaging the cell

Apocrine - where a portion of the cell is pinched off and released with the secretion

Holocrine - where the entire cell ruptures and bursts releasing its content and becoming apart of the secretion

Membranes line the body surfaces, with most consiting of epithelium supported by connective tissue, the main types of membranes include:

Mucous membranes - line body cavities that open to the outside of the cell EG; Digestive, repsiratory and urinary tract

Serous membranes - lines internal cavities and secretes fluid to reduce friction (not open to the outside environment). It has two layers, a parietal layer that lines the body cavity and a visceral layer that envelops the organs. It secretes a thin, watery transudate called serous fluid, which reduces friction between the contacting surfaces of the parietal and visceral layers

Cutaneous membranes - for protection and prevention of water loss, EG: skin

Synovial membranes - lines joints of the body, responsible for secreting synovial fluid fo lubrication and reduced friction.

Mucous made of stratified squamous epithelium and connective tissue
Serous is made of simple squamous epithelium
Cutaneous is made of stratified squamous epithelium and connective tissue
Synovial is made of loose connective tissue and no epithelium

Connective tissue is made up of two primary components, cells and extracellular matrix. The cells in connective tissue are either permanent (meaning they liveeside in connective tissue) or they can be migratory (come in for specific purposes and leave after). The permanent cells of the connective tissue is reponsible for producing and maintining the extracellular matrix. The extracellular matrix is made up of protein fibres such as collagen, and ground substance, which is a substance that provides the bulk of the connective tissue

Fibroplasts - secrete fibres and ground substance
Macrophages - undergo phagocytosis to remove waste
Mast cells - release histamine for inflammatory response
Plasma cells - produce antibodies
Adipocytes - store fat
Leukocytes (WBC) - Immunity and pathogen response

- Collagen fibres – Strong, flexible, resist stretching (e.g., tendons, ligaments)
- Elastic fibres – Stretch and recoil (e.g., lungs, arteries)
- Reticular fibres – Form soft supportive mesh (e.g., lymph nodes, spleen)

Proper connective tissue can be broken into
1) Dense connective tissue - Dense regular, dense irregular and elastic
2) Loose connective tissue - Areolar, adipose, reticular

Specialised connective tissue can be broken into
1) Cartilage - hyaline, elastic and fibrocartilage
2) Bone - compact / cortical or spongy / cancellous

Fluid connective tissue includes
1) Blood
2) Lymph

The shaft of the bone, providing strength and support
The ends of the bone, responsible for the formation of joints
Section of bone between diaphysis and epiphyses
Contains yellow marrow (fat storage)
a fibrous sheath that covers bones except for where there is cartilage / a joint. It contains the blood vessels and nerves that provide nourishment and sensation to the bone.
Lines medullary cavity for bone growth and remodelling
A glossy, smooth, translucent tissue that covers the ends of bones where they meet to form joints

Compact bone is dense and strong bone located on the outer layer of bone for weight-bearing

The fundamental component of compact bone is know as the harvesion system or osteons

Spongy bone has a porous structure and is located in the epiphyses and flat bones. Spongy bone provides lightness for compact bone, enhancing stability and movement. Moreover spongy bone contains spcaes for red bone marrow storage, the site of haemotopoesis (blood cell production)

1) Hyaline cartilage template serves as a framework for the bone to grow into
2) The formation of a primary ossification centre in the diaphysis of the long bone. Blood vessels invade the cartilage model, releasing osteoblasts (bone producing cells) which deposit bone around the model
3) A secondary ossiifcation centre forms in the epiphyses of the long bone. Again osteoblasts begin to deposit bone around the model
4) A layer of cartilage remains between the two formation centres, known as the epiphyseal plate. This plate will only fuse in adults lower limbs around age 25

Blood is a liquid connective tissue in the respect that it has a role in connecting the body itself, through processes such as the transportation of nutrients (oxygen, energy) or the removal of waste.

Plasma (50 - 55%)
- mainly water, with smaller amounts of proteins and solutes (eg; electroyltes)

Formed elements (45 - 50%)
- Red blood cells to carry oxygen
- White blood cells for immunity
- Platelets for clotting

Smooth muscular tissue
- Involuntary
- Lines internal organs, driving movement within the body eg; vasodilation
- non-striated, spindle shaped and uninucleated

Cardiac muscular tissue
- Involuntrary and highly specialised
- Lines the heart (walls of the heart)
- Straited, branched and uninucleated

Skeletal muscular tissue
- Volunatary
- Attached to the skeleton, repsonsible for producing body movements
- Striated, tubular and multinucleated because of their size

Neurons - Communicating cells that cannot divide under normal conditions, i.e. The neurons you have now are the neurons you are born with

Glial cells - The cells that support and repair the nervous tissue. They do this by producing myelin for protection and regulating the movement of ions for neural communication

Tissues are a group of similar cells working together for a shared and specific function whereas organs are comprised of multiple different types of tissue working togther for the same function.

For example, the heart, an organ, is comprised of muscular tissue (cardiac tissue), connective tissue (supporting the endothelium), nervous tissue and epithelial tissue (simple squamous Endothelium).

1st layer - Epidermis
2nd layer - dermis
3rd layer - hypodermis

- Made up of stratified squamous epithelium and is avascular, meaning that it lacks blood vessels and blood supply.
- The epidermis functions to provide protection, including waterproofing, barrier against pathogens and a surface protecting us from direct contact/damage
- The epidermis also provides sensation through Merkel cells for touch
- Desmosomes join epithelial cells in the epidermis together whilst hemidesmosomes join the epidermis to the basement layer of the epidermis, known as the stratum Basale

- The middle layer is known as the dermis and houses blood vessels, nerves, hair follicles, sweat and sebaceous glands.
- It is made up of dense irregular connective tissue, collagen and elastic fibers, providing strength, support and flexibility.
- Responsible for sensation via nerves and themroregulation via sweat glands

- The bottom layer is known as the hypodermis or the subcutaneous layer.
- This layer is made up of loose connective tissue and adipose tissue (fat storing loose connective tissue)
- This layer contains fat, large blood vessels and lymphatic vessels, for immunity, shock absorption and insulation and energy storage.

Skin renewal or epidermal turnover is the process whereby the skin replaces itself (every 28 days)
1) Basal cell proliferation
- Stem cells in the stratum basale (the basement layer of the epidermis, connecting the epidermis to dermis) divide to produce new keratinocytes
- Keratinocytes contain keratin, a protein that strengthens the skin

2) Mutation and Migration
- These new keratinocytes move upwards towards the surface, maturing and producing more keratine
- As they move they flatten and form abarrier via tight junctions

3) Keratinization
- Keratinization, also known as cornification, is the process whereby these cells become fully keratinized and begin to die, forming a tough, waterproof layer on the outermost layer of the epidermis

1) Gap junctions (direct contact)
2) Autocrine signalling - Cells release signaling molecules that bind to receptors on their own surface, triggering a response in the same cell
3) Paracrine signalling - Cells release signalling molecules that bind to receptors on the surface of other cells
4) Endocrine signalling - Cells release hormones into the bloodstream, which travel to distant target cells and affect them.

1) Chemical signal released by one cell
2) The target cell must have receptor proteins that can detect and respond to the signal
3) The binding of the signal to receptor protein
4) Activation of receptor protein casuing susbequent intracellular signalling
5) modification of exisiting proteins or production of new ones = A REPSONE

Neural signalling uses electrical signals (action potentials) and neurotransmitters to transport signals to other neurons whilst endocrine signalling involves the release of hormones or chemicals intot he blood stream to reach target cells.

Neural signalling is faster but short-lived comapred to endocrine signalling which is slower but long-lived (until the hormone is broken down)

Lipid-soluble hormones
• Insoluble in water and require carrier proteins in the blood to circulate them but they can readily pass through cell membranes
• Steroid hormones, thyroid hormones.
• These circulate bound to transport proteins
• Bind to receptors within target cells

Water-soluble hormones
• Are readily dissolved in blood and thus can be transported freely, but cannot easily pass through cell membranes
• Amine hormones (derived from amino acids), peptide and protein hormones
• These circulate freely in the plasma
• Bind onto receptors on the surface of the target cell (cell membrane)

The hypothalamus is a brain region located above the pituitary gland (a small pea sized gland sitting at the base of the brain). They are interconnected by the pituitary stalk (infundibulum) and a network of blood vessels, enabling effective communication and regulation of hormone release.

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

Eg: ADH and Oxytocin is from the pituitary gland via the production by neurosecretory cells of the hypothalamus

- 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

The thyroid gland is a butterfly-shaped gland located in the neck responsible for producing hormones that regulate metabolism, assist in thermoregulation, assist in energy production by allowing the use of glucose and fatty acids for ATP production

The adrenal glands are located on the top of each kidney and is divided into tow regions, the outer cortex and the medulla all covered by a capsule. The adrenal cortex is repsonsible for the production of glucocorticoids and androgens whilst the adrenal medulla produces catecholamines.

Glucocorticoids (steroids) like cortisol are responsible for Stress response, controlling protein breakdown, glucose formation, lipolysis, inflammation and immune responses

Androgens (sex hormones) are also made in the adrenal glands despite the ovaries and testes being the main producers. The adrenal cortex produces adrogens like DHEA, which are precursors to other sex hormones like estrogen and testosterone

Catecholamines including epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine which are the hormones are involved in the "fight-or-flight" response

- A cell body or soma that contains the nucleus and other organelles
- Dendrites, which are fine branching extensions at one end of the neuron which recieve messages from other neurons and direct towards the cell body
- An axon, which is a long extension of the cell body, conducting the action potential away from the cell body towards the axon terminal which release neurotransmitters. The axon is usually myelinated, meaning it is covered by a myeline sheath, insulating it and speeding up the electrical transmission

Efferent or Motor neurons are responsible for carrying signals from the CNS to the PNS and effector cells (Typically multipolar)

Afferent or Sensory neurons are responsible for carrying signals from the PNS to the CNS (Typically unipolar)

Interneurons are located within the CNS and are responsible for the transfer of information between sensory and motor neurons (Multi polar)

Astrocytes - star-shaped cells that maintain the blood-brain barrier and ensure the selective transport of substances between the bloodstream and brain
Oligodendrocytes - Form the myelin sheath around axons in the CNS, enhancing the efficiency of action potentials
Microglia (macrophages) - The immune defence of the CNS, engulfing pathogens, damaged cells and debris via phagocytosis
Ependymal cells - Line the ventricles of the brain and the central canal of the spinal cord, responsible for the production, circulation and regulation of cerebrospinal fluid (CBF)

Schwann cells - Form the myeline sheath around axons in the PNS, similar to oligodendrocytes except they myelinate one axon at a time compared to oligodendrocytes which myeliante mutliple simultaneously
Satellite cells - Functional equivalent of astrocytes in the PNS --> Regulating the microenvironemnt, movement of ions and nutrients. They also surrond and support the cell bodies of neurons within ganglia (clusters of neurons in the PNS)

Cerebrum (made up of both central hemispheres)
Diencephalon (thalamus, hypothalamus, epithalamus and subthalamus)
Brainstem (Pons, medulla oblongata and midbrain)
Cerebellum

Cerebrum - cognitive processes like decision-making, memory, emotions and voluntary motor control (movement)

Diencephalon - Thalamus acts a relay centre for sensory information and coordinates motor signals to the cerebral cortex whilst the Hypothalamus regulates autonomic functions like appetite, temperature and hormone secretion via the pituitary gland

Brainstem - Controls motor and visceral functions (the physiological operations of the internal organs), particularly subconscious motor control (reflexes)

Cerebellum - Coordinates and fine-tunes voluntary muscle movements and balance, helping to maintain posture and motor learning

Frontal lobe - higher cognitive processes, such as decison making. Contains the primary motor cortex (voluntary movement) and areas responsible for speech production (broca's area)

Parietal lobe - processes sensory information like touch and pain. Contains the primary somatosensory cortex, responsible for mapping sensations all over the body

Temporal lobe - handles auditory processing, comprehension and memory formation. Houses the primary auditory cortex and the hippocampus, essential for long-term memory

Occipital lobe - Dedicated to visual processing, including recognition and colours. Holds the primary visual cortex

A typical cell has a resting membrane potential around -70mV with a greater concentration of Potassium (K) and negatively charged proteins inside the cell compared to the outside of the cell with a higher conenctration of sodium (Na), chloride (Cl) and Calcium (Ca) --> All ions

This uneven distrubution creates an electrical gradient

A combination of three processes
- Ion channels / leak channels
- Selective permeability
- The soduim-potassium pump

This mechanism involves the active transport of 3 sodium molecules (Na) out and 2 potassium molecules (K) into the cell to maintain proper concentration of potassium ions K+ and sodium ions Na+ inside and outside of the cell.

Both K and Na are cations, meaning they are negatively charged and thus carry positive charge away with them due to an electrostatic attraction / Ionic bonding

Ion channels are specialized protein structures embedded in cell membranes that act as selective tunnels, allowing specific charged ions to pass through down their electrochemical gradient. The main types include:
- Leak channels: allows the passive diffusion of ions across the mebrane
- Ligate-gated channels: Opens when a specific chemical (ligate) binds to the channel, allowing ion flow
- Mechnaically-gated channels: Open in response to mechanical stimuli like pressure, vibration
- Voltage-gated channels: Open or close in response to changes in membrane potential (action potentials) --> Depolarisation is a voltage-gated channel process (voltage-gated sodium channels which allow Na to rush into the cell, making the inside more positive)

An action potential is a rapid, temporary change in membrane potential that allows neurons to transmit electrical signals

1) The neuron is a rest, with a high concentration of K inside the cell and a NA outside the cell. Leak channels allow K to exit the cell, carrying with it positive charge, mainting the RMP of -70mV whils the NA / K pump also actively transports ions to preserve this gradient
2) Depolarisation occurs as there is a sudden influx of positive ions in response to a stimulus (neurotransmitters etc), Once the membrane potential reaches the threshold of -55mV, the axon hillock’s voltage-gated Na channels open, allowing Na to rush into the cell, carrying with it positive ions, thus making the cell less negative/more positive.
3) Once the membrane potential reaches +30mV the voltage-gated Na channel deactivates whilst the Voltage-gated K channel opens allowing K to exit the cell, carrying with it positive ions, returning the membrane potential to negative in a process known as REPOLARISATION
4) These K channels stay open for slightly longer than needed, causing temporary HYPERPOLARISATION. The K channels the deactivate and the sodium-potassium pump returns -80mV to RMP (-70mV)

Action potentials reach the axon terminal where neurotransmitter release occurs as the voltage-gated calcium channels open, causing an influx of Ca, triggering the exocytosis of neutransmitter filled vesicles. Ultimately, once released, these neurotransmitters bind to ligate-gated channels on the target cell / neuron, causing an action potential (<-- This is the stimuli for depolarisation)

Myelinated axons are quicker and more efficient due to saltatory conduction (a rapid method of nerve impulse transmission in myelinated axons where action potentials "jump" between the nodes of Ranvier, the gaps in the myelin sheath, rather than traveling continuously along the entire axon membrane.)

Unmyelianted axons are thus slower and less energy efficient as they use continuous conduction rather than saltatory conduction

Communication between neurons is referred to as synaptic transmission. A synapse is the junction between neurons or a neuron and an effector. There are two kinds of synaptic transmissions:
Electrical Synapse
- Where gap junctions (connexons) connect cells and allow the transfer of information to synchronise the activity of a group of cells
Chemical Synapse
- The one-way transfer of information from a presynaptic neuron to a postsynaptic neuron via neurotransmitters

1) The action potential travels down the axon of the presynaptic neuron, reaching the axon terminal
2) Voltage-gated calcium channels open, causing an influx of Ca into the cell, ultimately causing the exocytosis of neurotransmitter-filled vesicles
3) These neurotransmitters diffuse across the synaptic cleft and bind to ligate-gated ion channels (receptors) on the post-synaptic membrane
4) This binding of the neurotransmitters on the dendrites of the post-synaptic neuron cause the opening of ligate-gated ion channels. Depending on the receptor this can result in the:
- Excitatory Post-Synaptic potential (EPSP) causing the depolarisation of the post-synaptic neuron due to influx of Na --> Causing another action potential to be fired if -55mV is reached
- Inhibitory Post-Synaptic potential (IPSP) causing the hyperpolarisation of the post-synaptic membrane potential due to loss of K or entry of Cl --> This makes the membrane potential more negative meaning the action potential is less likely to occur.

The ability of neurons to modify the strength of existing synapses, as well as form new synaptic connections, is called neuroplasticity. This repeated use of a synapse leads to changes in its strength or efficiency --> Known as synaptic plasticity

Long-term Potentiation (LTP)
- Persistent strengthening of synapses based on recent / reoccurring patterns of activity (high frequency)

Long-term Depression (LDP)
- Persistent weakening of synapses due to low-frequency or prolonged stimulation

High frequency stimulation of a synapse increases the amounts of neurotransmitters released and the sensitivity of the post-synaptic neuron by adding more receptors to its membrane and improving intracellular signalling pathways.
- This ultimately results in faster and more reliable communication between neurons  LTP

A stroke occurs as bloodflow to the brain is blocked or interrupted, depriving brain tissue of oxygen and nutrients, ultimately causing cell death in affected areas. This cell death results in;
• Loss of function (speech, movement cognition), depending on the area damaged
• Disruption of neuron communication, therefore weakening of synaptic plasticity.

However after a stroke, the brain can ‘rewire itself’ by reorganising neural pathways and forming connections to compensate for lost functions

The sensory nervous system involves detecting a sensation, which is the conscious or subconscious awareness of changes in the internal or external environment, detected by sensory receptors

Sensory reeptors are classified depending on stimulus type or location

Receptors by Stimulus Type:
Mechanoreceptors - detect touch, pressure, vibration and strech
Thermoreceptors - respond to temperature change
Photoreceptors - respond to changes in light intensity and availability
Nociceptors - detect pain from damage or threat (eg; extreme hot/cold, excessive pressure)
Chemoreceptors – detect chemicals in solution, air, smelled or tasted
Osmoreceptors – detect changes in osmotic pressure (in the hypothalamus)

Receptors by Location:
Exteroceptors – respond to external stimuli, either outside the body or near body surface (touch, pain, vision)
Interoceptors (visceroceptors) – monitor internal environment (e.g., blood pH).
Proprioceptors – like interoceptors in the respect that they respond to internal stimuli, however the location is much more restricted, eg; muscle tissue. Detects body and limb positioning and advise the brain on this information (in muscles, joints and tendons)

Meissner's corpuscles detect light pressure and touch on the dermal papillae (fingertips) --> Extend from dermis to epidermis

Merkel discs are found in the basal epidermis and detect pressure and texture

Pacinian corpuscles are found in the hypodermis or subcutaneous layers and are responsible for detecting deep pressure and high frequency vibrations

Ruffini endings / corpuscles are slowly adapting mechanoreceptors located in the cutaneous tissue between the dermal papillae and the hypodermis (DERMIS)

Free nerve endings are found throughout the epidermis and dermis and can work as many different types of receptors, eg; can detect temperature (thermoreceptors), mechanical stimuli (touch, pressure, stretch) or danger (nociception).

Proprioceptors are sensory receptors that provide the body with information about its position and movement, also known as the sense of body position or proprioception.

Receptors within skeletal muscle spindles detect muscle stretch

Receptors within Tendons are called golgi tendon organs, which detect and sense tendon tension

Receptors within synovial joints are known as joint kineasthetic receptors and are responsible for sensing joint angle and motion

1) Odor molecules bind to receptors on olfactory sensory neurons within the nasal cavity

2) Signals travel via the olfactory nerve to the olfactory bulb

3) This information is processed by the olfactory cortex in the temporal lobe

1) Taste buds on the tongue detect chemicals within foods
2) Receptors send signals via facial, glossopharangyeal and vagus nerves
3) Information travels to the gustatory cortex in the parietal lobe

1) Light enters the eye and focusses on the retina
2) Photoreceptors (rods and cones) detect grey, white and colours and convert this to electromagentic waves / signals
3) The signal is passed through the optic nerve towards the thalamus and ultimately the visual cortex in the occipital lobe

1) Sound waves enter the ear and travel down the ear canal towards the ear drum (tympanic membrane)
2) The ear drum converts this sound to mechanical energy via its vibrations.
3) The three small bones in the mid ear (Ossicles --> Hammer, Stirrup and Anvil) amplify these sounds and move it towards the oval window
4) The vibrations push on the oval window creating pressure waves inside of the fluid-filled cochlea. These fluid waves move through the spiral structure where specialised hair cells begin to detect thuis mechanical energy and transfer it to electrical energy as they direct it to the auditory nerve
5) This information passes through the auditory nerve and sends these electrical signals made by the bending of the hair cells to the auditory cortex in the temporal lobe of the brain where it is processed

The neuromuscular junction (NMJ) is a specialized synapse where a motor neuron communicates with a skeletal muscle fiber to trigger muscle contraction.
It involves chemical transmission — the release of a neurotransmitter to pass the signal from the nerve to the muscle.

- Action potential reaches the axon terminal of the presynaptic motor neuron
- Voltage-gated Ca ion channels open causing an influx of Ca into the presynaptic motor neuron, causing synaptic vesicles carrying neurotransmitters (acetylcholine or ACh) to leave the cell via exocytosis
- In the synaptic cleft (the small gap between the neuron and muscle cell, the enzyme acetylcholinesterase (AChE) is found.
- ACh binds to the Nicotinic ACh receptors on the muscle cell, causing this ligand-gated ion channel to open.
- This receptor opens allowing Na to enter the cell and K to exit the cell in a process known as depolarisation. If the depolarisation reaches the membrane potential threshold (EPSP), a muscle action potential is triggered (muscle contraction) known as ‘endplate potential’.
- ACh is broken down by AChE into acetate and choline

The somatic (body cells) motor system is responsible for voluntary skeletal muscle movement. There are two basic pathways involving two different motor neurons. The upper motor neuron’s lie entirely within the CNS, particularly their cell bodies lie in the primary motor cortex. Their axons descend through the brainstem and spinal cord playing crucial roles in initiating and controlling voluntary movements by sending the signals to lower motor neurons.
- Note: UMN’s do not directly innervate muscles but rather synapse onto lower motor neurons in the brainstem or spinal cord which will innervate muscles.

Lower motor neurons (LMM’s) are located within the brainstem and spinal cord with their axons projecting into the PNS via the; ventral roots, spinal nerves or cranial nerves. LMN’s are responsible for directly innervating skeletal muscle as they carry motor commands from the upper motor neurons to the muscle fibres, triggering contraction.

- Neural Activation: An action potential travels from an upper motor neuron to a lower motor neuron, which releases acetylcholine (ACh) at the neuromuscular junction (NMJ). ACh binds to receptors on the sarcolemma (muscle cell membrane), triggering depolarization.
- Calcium Release: The action potential spreads through T-tubules, stimulating the sarcoplasmic reticulum to release calcium ions (Ca²⁺) into the cytoplasm.
- Crossbridge Formation: Calcium binds to troponin, exposing actin binding sites. Myosin heads attach to actin filaments, forming crossbridges within the sarcomere (the contractile unit of skeletal muscle).
- Contraction: Myosin heads pivot, pulling actin filaments inward. This shortens the sarcomere, generating muscle contraction.

A reflex arc is the simplest functional unit of the nervous system that allows for rapid automatic responses to stimuli, relfexes help protect the body from damage and maintain homeostasis

1. Sensory receptor - detects a stimulus (eg; strech, pain, heat etc)

2. Sensory (afferent) neuron - carries the impulse towards the spinal cord or brain

3. Integration centre - located within the grey matter of the spinal cord, potentially involving one or more interneurons (for polysnaptic reflexes) whilst in monosynaptic reflexes the afferent neuron synapses directly with a efferent neuron

4. Motor (efferent) neuron - conducts impulses away from the CNS to an effector

5. Effector - the muscle or gland that responds to the stimulus. For somatic reflexes its skeletal muscle, whilst for autonomic reflexes it could be smooth or cardiac muscle

1. Central pattern generators (CPG's) - these are networks in the spinal cord that generate rhythmic, repetitive movements like walking

2. Motor cortex - the region of the brain important for iniatiating voluntary movement and planning / modyfing gait to avoid obstacles etc

3. Cerebellum - coordinates timing and smooths movements

4. Sensory feedback systems - proprioceptors (muscle spindles, golgi tendon groups) which monitor postioning and tension, the visual system which provides guidance, especially on uneven surfaces.

The autonomic nervous system (ANS) is a division of the peripheral nervous system that regulates involuntary functions such as heart rate, digestion and glandular activity. The ANS has two main branches with opposing effects:

- The parasympathetic nervous system (Rest and Digest)
- The sympathetic nervous system (Fight or Flight)

The role of this system is to promote energy conservation and the restoration of body energy during rest. It supports functions like digestion, nutrient absorption and recovery.

General effects of this system include the slowing of heart rate, stimlation of digestion and salvia production, constriction of pupils and bronchioles

The role of the sympathetic nervous system is to prepare the body for emergency or high stress situations. It does this by activating systems that help with rapid responses.

General effects of this system include increased heart rate and blood pressure (via vasoconstriction), dilation of pupils to enhance visual acuity, relaxing of airways t increase o2 uptake, stimulates glucose release from liver, stimulates the release of catecholamines from the Adrenal medulla

Pacemaker cells are specialized heart cells that initiate the electrical impulses that cause the heart to beat, these cells have a unique ability to spontaneously generate electrical impulses, allowing them to act as the heart's natural pacemaker.

Skeletal muscle is voluntarily controlled via the somatic nervous system, it does not feature any pacemaker cells. There is no electrical coupling, rather each fibre contracts independantly. Skeletal muscle is charachterised by rapud onset and short durations to produce short and foreceful bursts of contraction. AP's spread down the T-tubules are invanginations on the sarcolemma (muscle cell membrane). The source of calcium is from the Sarcoplasmic reticulum (SR). Lastly skeletal muscle contraction is controlled via neural input as its voluntary / involuntary --> neuromuscular junctions

Cardiac muscle is involuntarily controlled by the autonomic nervous system and by pacemaker cells. Cardiac muscles are electrically coupled via gap junctions to produce synchronised contractions. Cardiac muscle contracts intermediately and is rapid but rhythmic to maintain homeostasis. AP spreads from cell to cell via gap junctions with the calcium being sourced from both Sarcoplasmic reticulum and extracellular Ca. Cardiac muscle has the ability to contract spontaneously via pacemaker cells and neural input

Smooth muscle is involuntarily controlled by the autonomic nervous system and by pacemaker cells. Similarly, smooth muscle is also electrically coupled via gap junctions, partcularly in single-unit smooth muscle (for example, your intestines) but not in multi-unit smooth muscle (for example cilliary muscles of the eye). Smooth muscle has a slow onset but a long duration as it is sustained vy contractions. AP's can spread via gap junctions in single-unit smooth muscle. Calcium is predominantly sourced from extracellular calcium with some coming from sacroplasmic reticulum (SR). Lastly, smooth muscle is controlled by neural, hormonal or local factors including strech, pH, neurotransmitters etc.