Muscle Tissue and Skeletal Muscle Anatomy

Is the only tissue in the body that is specialized for contraction.

Muscle contraction allow body parts movement.

The body contain three types of muscle tissue:- Skeletal – smooth –cardiac.

Functions

Movement – Muscles produce body movements and allow walking, running, and other physical activities.
2. Maintain posture – Continuous muscle activity helps keep the body upright and properly aligned.
3. Respiration
4. Production of body heat – Muscle contraction produces heat, a process called thermogenesis.
5. Communication – Facial and body movements help express emotions and communicate.
6. Heart beat – Cardiac muscle contracts rhythmically to pump blood.
7. Contraction of organs and vessels - Smooth muscle contracts in the walls of organs and blood vessels, supporting digestion, blood pressure regulation, and other vital processes.
8. Joint stabilization - Muscles support and protect joints during movement.

Skeletal Muscle Characteristics

Makes up 40% of body weight

Named because attached to bones (skeleton)

Many nuclei per cell (near periphery)

Striated

Longest of muscle types

Skeletal muscle is striated and voluntary, meaning it has a striped appearance under a microscope and can usually be controlled consciously. It is attached to bones and is responsible for:

Conscious movement

Locomotion

Posture maintenance

Heat production

Facial expressions

Abilities of Skeletal Muscles

Contractility: The ability to shorten and produce force.

Excitability: respond to stimulus

Extensibility: can stretch

Elasticity: The ability to return to its original length after being stretched or contracted.

SKELETAL MUSCLE STRUCTURE

Skeletal muscles are attached to bones by tendons.

Muscles are attached to each other by ligaments or aponeurosis

Muscles are made of fascicles > fibers > myofibrils > filaments.
Muscles are organized into several levels:

Muscle: The complete organ.

Fascicles: Bundles of muscle fibers.

Muscle fibers: Individual muscle cells.

Myofibrils: Contractile structures inside muscle fibers.

Filaments: Protein structures, mainly actin and myosin, that interact to produce contraction.

Dense connective tissue surround each fiber, each fascicle and the entire muscle.
.

Epimysium:

connective tissue that surrounds entire skeletal muscle (outside)

Muscle fasciculus:

bundle of muscle fibers

Perimysium:

connective tissue around each muscle fasciculus

Muscle fiber:

- skeletal muscle cells

- many nuclei

Endomysium:

connective tissue that surrounds

Muscle fiber

A muscle fiber is a multinucleated long, thin muscle cell that extend the full length of the muscle.

The cell membrane of the muscle fiber is called the sarcolemma and its cytoplasm is called sarcoplasm

Each muscle fiber is made of many thin threads called myofibrils.

The myofibril

Myofibrils are the contractile elements of each muscle fiber.

A myofibril is made from two types of protein filaments:-

Actin filaments:- thin filaments.

Myosin filaments:- thick filaments.

The arrangement of actin & myosin filaments within a muscle fiber produce the muscle striations.

The sarcomere

A sarcomere is the smallest part of a myofibril that is capable of contraction.

Each sarcomere extend from one ‘z’ line to the next ‘z’ line.

The actin filaments are attached to the ‘z’ lines while the myosin filaments extend in-between the actin filaments.









MUSCLE EXCITATION

In order for muscles to contract they must be stimulated by nerve signals from either the brain or the spinal cord.

Nerve signals are carried by motor neurons to each muscle fiber.

One motor neuron plus all the muscle fibers to which the neuron is attached form a motor unit.

MUSCLE EXCITATION AND CONTRACTION

When a nerve signal carried by a motor neuron reach the axon tip, acetylcholine is released to stimulate the muscle fiber.

The attachment of acetylcholine to the sarcolemma will trigger a series of reactions that causes the muscle fiber sarcomeres to contract.

{sliding filaments theory}

Sliding Filament Theory

The sliding filament theory, proposed through the work of Hugh Huxley and Jean Hanson in 1954, explains how muscles contract. According to the theory, the thick myosin filaments slide past the thin actin filaments inside muscle fibers. The filaments themselves do not become shorter. Instead, their sliding movement causes the muscle fiber and the entire muscle to shorten.

In simplified terms:

A stimulus causes the muscle fiber to activate.

Myosin interacts with actin.

Myosin pulls the actin filaments inward.

The distance between the ends of the contractile unit decreases.

The muscle contracts and produces movement.

Sarcomeres shorten because thick and thin filaments slide past one another

Thin filaments move towards the center of the sarcomere from both ends

MUSCLE CONTRACTION

Muscle twitch:- a single muscle contraction in response to a single stimulus or nerve signal.

Graded response:- as the stimulus strength increases, contractions get stronger and stronger.

Tetanic contractions:- continuous contractions without relaxations

Skeletal Muscle Anatomy

Origin: no movable end

Insertion: movable end

Belly: middle

Synergists: muscles that work together

Antagonist: muscles that oppose each other

Roles of Muscles During Movement
Muscles can be classified according to how they work together:
Agonist: The prime mover that initiates and performs a particular action. For example, the biceps acts as an agonist during elbow flexion.
Antagonist: A muscle that opposes the action of another muscle. For example, the triceps opposes the biceps during elbow flexion.
Synergist: A muscle that works together with another muscle to assist or refine a movement.
• Agonists and antagonists often work in pairs. When one muscle contracts, the opposing muscle relaxes or controls the movement.

Muscle Nomenclature
• Muscles can be named according to several features.
• A muscle may be named after the region or bone where it is located. For example, the tibialis anterior is located along the front of the tibia.
Origin and Insertion
Origin: The attachment of a muscle to the relatively immovable or less movable bone.
Insertion: The attachment of a muscle to the more movable bone or structure.
• When a muscle contracts, its insertion usually moves toward its origin.

Muscles are named according to:

Location: Ex. tibialis anterior

Origin/insertion: Ex. sternocleidomastoid

Size: Ex. gluteus maximus
Muscle names may indicate size:
Maximus: Largest
Minimus: Smallest
Vastus: Large or broad

Shape: Ex. deltoid (triangular)
A muscle may be named according to its shape, such as:
Triangular
Circular
Trapezoid

Function: Ex. Masseter
-Some muscles are named according to their main action or function. The masseter, for example, is associated with chewing.
• Muscle Belly : The belly is the thick, central, and fleshy part of a muscle. It lies between the muscle’s attachments.

Muscles of Head and Neck

Occipitofrontalis: raises eyebrows (forehead)

Orbicularis oculi: allows blinking (eyes)

Orbicularis oris: kissing muscle (mouth)

Zygomaticus: smiling muscle (cheek)

Masseter: A major muscle of mastication, or chewing.

Buccinator: Compresses the cheek and assists with actions involving the mouth, such as chewing, sucking, and blowing.

Sternocleidomastoid: Helps flex, rotate, and tilt the neck. Its name refers to its attachments to the sternum, clavicle, and mastoid process.

Trapezius: A large muscle extending across the upper back and neck. It helps move and stabilize the shoulders and is associated with the nape of the neck.

Platysma: A thin muscle at the front of the neck that helps move the lower lip and mandible and tighten the skin of the neck.




Thoracic Muscles

External intercostals:

elevate ribs for inspiration (breath in)

Internal intercostals:

depress ribs during forced expiration (breath out)

Diaphragm:
moves during quiet breathing

Abdominal Wall Muscles

Rectus abdominis:

- center of abdomen (abs)

- compresses abdomen

External abdominal oblique:

- sides of abdomen

- compresses abdomen

Internal abdominal oblique:

compresses abdomen

Transverse abdominis:

compresses abdomen



Upper Limb Muscles

Trapezius:

- shoulders and upper back

- extends neck and head

Pectoralis major:

- chest

- elevates ribs

Serratus anterior:

- between ribs

- elevates ribs

Deltoid:

- shoulder

- abductor or upper limbs

Triceps brachii:

- 3 heads

- extends elbow

Biceps brachii:

- “flexing muscle”

- flexes elbow and shoulder

Brachialis:

flexes elbow

Latissimus dorsi:

- lower back

- extends shoulder
































Muscles of Upper Leg
Quadriceps femoris
4 thigh muscles

Rectus femoris:

- front of thigh

- extends knee and

Vastus lateralis:

extends knee

Vastus medialis:

extends knee

Vastus intermedius: extends knee

Gracilis:

adducts thigh and flexes

Biceps femoris, semimembranosus, semitendinosus:

- hamstring

- back of thigh

- flexes knee, rotates leg, extends hip

Muscles of Lower Leg

Tibialis anterior:

- front of lower leg

- inverts foot

Gastrocnemius:

- calf

- flexes foot and leg

Soleus:

- attaches to ankle

- flexes foot
















Body Movements

Flexion – bending a body part

Extension – straightening a body part

Hyperextension – extending a body part past the normal anatomical position

Dorsiflexion – pointing the toes up

Plantar flexion – pointing the toes down

Abduction – moving a body part away from the anatomical position

Adduction – moving a body part toward the anatomical position
Note: A useful memory aid is that abduction takes a body part away, while adduction adds it back toward the body.

Circumduction – moving a body part in a circle

Pronation – turning the palm of the hand down

Supination – turning the palm of the hand up

Inversion – turning the sole of the foot med ially

Eversion – turning the sole of the foot laterally

Retraction – moving a body part posteriorly

Protraction – moving a body part anteriorly

Elevation – lifting a body part; for example, elevating the shoulders as in a shrugging expression

Depression – lowering a body part; for example, lowering the shoulders

















































Cardiac Muscle Characteristics

Heart

1 centrally located nucleus/cell

Striated

Rich in mitochondria

Intercalated disks: special cell junctions that allow cells to act

Cardiac muscle is striated but involuntary. It is found only in the heart and is also called the myocardium.

Its main function is to contract rhythmically and pump blood throughout the body.


Smooth Muscle or Visceral Muscle Characteristics

Found on organs

1 centrally located nucleus/cell

Not striated

Less actin and myosin

Under involuntary control

Smooth muscle is non-striated and involuntary, so it cannot usually be controlled consciously. It forms the walls of many internal organs and blood vessels.






Disorders and Diseases of the Muscular System

Musculoskeletal Disorders

are injuries that occur in muscles or associated tissues (such as tendons) because of biomechanical stresses. They may be caused by sudden exertion, over-exertion, repetitive motions, or long periods maintaining awkward positions. Musculoskeletal disorders are often work- or sports-related, and generally just one or a few muscles are affected. They can often be treated successfully, and full recovery can be very likely. The disorders include muscle strains, tendinitis, and carpal tunnel syndrome.

Muscle strain

is an injury in which muscle fibers tear as a result of overstretching. A muscle strain is also commonly called a pulled muscle or torn muscle. (Strains are often confused with sprains, which are similar injuries to ligaments.) Depending on the degree of injury to muscle fibers, a muscle strain can range from mildly to extremely painful. Besides pain, typical symptoms include stiffness and bruising in the area of the strained muscle.

Tendinitis

is inflammation of a tendon that occurs when it is over-extended or worked too hard without rest. Tendons that are commonly affected include those in the ankle, knee, shoulder, and elbow. The affected tendon depends on the type of use that causes the inflammation. Rock climbers tend to develop tendinitis in their fingers, while basketball players are more likely to develop tendinitis in the knees, to name a few examples.

Sprains and strains

Sprains are common injuries that occur due to stretching or tearing of tough bands of fibrous tissue that connect bones together, called ligaments. Strains occur due to a stretch or tear of muscle or tendons.

Muscle cramps

Characterized as an involuntary contraction of one or more of your muscles and is sometimes referred to as a “charley horse.” These muscle cramps make it temporarily impossible to use the affected muscle with cases typically occurring during hot weather, during exercise, or during physical labor. It is recommended to avoid dehydration and to stretch your muscles to prevent muscle cramps.

Myotonia

Characterized by the muscles relaxing slowly after contraction or stimulation. Common problems with this condition include not being able to release the grip on certain objects or having trouble walking. Myotonia can affect any muscle group, with patients needing to make repeated efforts to calm down the muscles to improve the condition.

Neuromuscular disorders

are systemic disorders that occur because of problems with the nervous control of muscle contractions, or with the muscle cells themselves. These disorders are often due to faulty genes and not due to biomechanical stresses. Other system-wide problems, such as abnormal immune system responses, may also be involved in neuromuscular disorders.

Neuromuscular disorders generally affect most or all of the muscles in the body. The disorders also tend to be progressive and incurable. However, in most cases, treatment is available to slow the disease progression or to lessen the symptoms. Examples of neuromuscular disorders include muscular dystrophy, myasthenia gravis, and Parkinson’s disease.

Dermatomyositis

is an inflammatory disease characterized by muscle weakness and a distinctive rash. The condition can occur in both children and adults, affecting mostly females. Skin changes are often described as appearing violet-colored or dusky red, most commonly on the face, eyelids, knuckles, elbows, knees, chest, and back. Rashes are often painful and itchy and are the first sign of dermatomyositis. Muscle weakness of the hips, thighs, shoulders, upper arms, and neck are commonly observed. Weakness can affect both sides of the body and become progressively

Muscular dystrophy

is a genetic disorder caused by defective proteins in muscle cells. It is characterized by progressive skeletal muscle weakness and death of muscle cells and tissues. Muscles become increasingly unable to contract in response to nervous stimulation.

Myasthenia gravis

is a genetic neuromuscular disorder characterized by fluctuating muscle weakness and fatigue. It occurs more commonly in women, and generally begins between the ages of 20 and 40.

Cerebral palsy

A broad term used to describe impairment or loss of motor function as a result of brain damage. It is believed that this damage occurs while still in the mother’s womb, as those with cerebral palsy are born with it. However, there are cases where the development of cerebral palsy can occur after birth. This condition affects muscle control, body movement, muscle coordination, reflexes, muscle tone, and balance.

Parkinson’s disease

is a degenerative disorder of the central nervous system that mainly affects the muscular system and movement. Four motor signs and symptoms are considered defining in Parkinson’s disease: muscle tremor (shaking), muscle rigidity, slowness of movement, and postural instability. Tremor is the most common and obvious symptom, and it most often occurs in a limb that is at rest, so it disappears during sleep or when the patient moves the limb voluntarily. Difficulty walking eventually develops, and dementia is common in the advanced stages of the disease. Depression is common, as well.

Amyotrophic lateral sclerosis

ALS is characterized by muscle weakness and atrophy—muscle wasting. It is due to the degeneration of upper and lower motor neurons of the body that are responsible for voluntary movement. Affected individuals ultimately lose their ability to initiate and control all voluntary movement, though bowel and bladder function, as well as eye movements, are typically spared. While behavioral and cognitive functioning usually remains intact, a small percentage may show signs of frontotemporal dementia. The disease can strike at any age but most commonly develops between the ages of 55 and 75.

Myalgia

Myalgia means muscle pain. It can result from injury, overuse, infection, inflammation, or other conditions.

Spasm

A muscle spasm is an involuntary contraction of a muscle or group of muscles. It may be sudden, painful, and difficult to control.

Myositis

Myositis is inflammation of muscle tissue. It may cause weakness, pain, and difficulty moving.

Fibrositis

Fibrositis refers to inflammation or irritation involving muscle fibers and surrounding connective tissues. The term has historically been used for painful soft-tissue conditions.

Atrophy

Muscle atrophy is the wasting or shrinking of muscle tissue, resulting in a loss of muscle mass. It may occur because of inactivity, illness, nerve damage, malnutrition, or aging.

Hypertrophy

Muscle hypertrophy is an increase in muscle size or bulk. It commonly occurs when muscles adapt to repeated resistance or workload, such as strength training.









MUSCULAR SYSTEM

Introduction:
The human body has more than 600 individual muscles. Muscles cause bones and supported structures to move by alternating between contraction and relaxation.

Muscle tissue

Is the only tissue in the body that is specialized for contraction.

Muscle contraction allow body parts movement.

The body contain three types of muscle tissue:- Skeletal – smooth –cardiac.

Functions

Movement – Muscles produce body movements and allow walking, running, and other physical activities.
2. Maintain posture – Continuous muscle activity helps keep the body upright and properly aligned.
3. Respiration
4. Production of body heat – Muscle contraction produces heat, a process called thermogenesis.
5. Communication – Facial and body movements help express emotions and communicate.
6. Heart beat – Cardiac muscle contracts rhythmically to pump blood.
7. Contraction of organs and vessels - Smooth muscle contracts in the walls of organs and blood vessels, supporting digestion, blood pressure regulation, and other vital processes.
8. Joint stabilization - Muscles support and protect joints during movement.

Skeletal Muscle Characteristics

Makes up 40% of body weight

Named because attached to bones (skeleton)

Many nuclei per cell (near periphery)

Striated

Longest of muscle types

Skeletal muscle is striated and voluntary, meaning it has a striped appearance under a microscope and can usually be controlled consciously. It is attached to bones and is responsible for:

Conscious movement

Locomotion

Posture maintenance

Heat production

Facial expressions

Abilities of Skeletal Muscles

Contractility: The ability to shorten and produce force.

Excitability: respond to stimulus

Extensibility: can stretch

Elasticity: The ability to return to its original length after being stretched or contracted.

SKELETAL MUSCLE STRUCTURE

Skeletal muscles are attached to bones by tendons.

Muscles are attached to each other by ligaments or aponeurosis

Muscles are made of fascicles > fibers > myofibrils > filaments.
Muscles are organized into several levels:

Muscle: The complete organ.

Fascicles: Bundles of muscle fibers.

Muscle fibers: Individual muscle cells.

Myofibrils: Contractile structures inside muscle fibers.

Filaments: Protein structures, mainly actin and myosin, that interact to produce contraction.

Dense connective tissue surround each fiber, each fascicle and the entire muscle.
.

Epimysium:

connective tissue that surrounds entire skeletal muscle (outside)

Muscle fasciculus:

bundle of muscle fibers

Perimysium:

connective tissue around each muscle fasciculus

Muscle fiber:

- skeletal muscle cells

- many nuclei

Endomysium:

connective tissue that surrounds

Muscle fiber

A muscle fiber is a multinucleated long, thin muscle cell that extend the full length of the muscle.

The cell membrane of the muscle fiber is called the sarcolemma and its cytoplasm is called sarcoplasm

Each muscle fiber is made of many thin threads called myofibrils.

The myofibril

Myofibrils are the contractile elements of each muscle fiber.

A myofibril is made from two types of protein filaments:-

Actin filaments:- thin filaments.

Myosin filaments:- thick filaments.

The arrangement of actin & myosin filaments within a muscle fiber produce the muscle striations.

The sarcomere

A sarcomere is the smallest part of a myofibril that is capable of contraction.

Each sarcomere extend from one ‘z’ line to the next ‘z’ line.

The actin filaments are attached to the ‘z’ lines while the myosin filaments extend in-between the actin filaments.









MUSCLE EXCITATION

In order for muscles to contract they must be stimulated by nerve signals from either the brain or the spinal cord.

Nerve signals are carried by motor neurons to each muscle fiber.

One motor neuron plus all the muscle fibers to which the neuron is attached form a motor unit.

MUSCLE EXCITATION AND CONTRACTION

When a nerve signal carried by a motor neuron reach the axon tip, acetylcholine is released to stimulate the muscle fiber.

The attachment of acetylcholine to the sarcolemma will trigger a series of reactions that causes the muscle fiber sarcomeres to contract.

{sliding filaments theory}

Sliding Filament Theory

The sliding filament theory, proposed through the work of Hugh Huxley and Jean Hanson in 1954, explains how muscles contract. According to the theory, the thick myosin filaments slide past the thin actin filaments inside muscle fibers. The filaments themselves do not become shorter. Instead, their sliding movement causes the muscle fiber and the entire muscle to shorten.

In simplified terms:

A stimulus causes the muscle fiber to activate.

Myosin interacts with actin.

Myosin pulls the actin filaments inward.

The distance between the ends of the contractile unit decreases.

The muscle contracts and produces movement.

Sarcomeres shorten because thick and thin filaments slide past one another

Thin filaments move towards the center of the sarcomere from both ends

MUSCLE CONTRACTION

Muscle twitch:- a single muscle contraction in response to a single stimulus or nerve signal.

Graded response:- as the stimulus strength increases, contractions get stronger and stronger.

Tetanic contractions:- continuous contractions without relaxations

Skeletal Muscle Anatomy

Origin: no movable end

Insertion: movable end

Belly: middle

Synergists: muscles that work together

Antagonist: muscles that oppose each other

Roles of Muscles During Movement
Muscles can be classified according to how they work together:
Agonist: The prime mover that initiates and performs a particular action. For example, the biceps acts as an agonist during elbow flexion.
Antagonist: A muscle that opposes the action of another muscle. For example, the triceps opposes the biceps during elbow flexion.
Synergist: A muscle that works together with another muscle to assist or refine a movement.
• Agonists and antagonists often work in pairs. When one muscle contracts, the opposing muscle relaxes or controls the movement.

Muscle Nomenclature
• Muscles can be named according to several features.
• A muscle may be named after the region or bone where it is located. For example, the tibialis anterior is located along the front of the tibia.
Origin and Insertion
Origin: The attachment of a muscle to the relatively immovable or less movable bone.
Insertion: The attachment of a muscle to the more movable bone or structure.
• When a muscle contracts, its insertion usually moves toward its origin.

Muscles are named according to:

Location: Ex. tibialis anterior

Origin/insertion: Ex. sternocleidomastoid

Size: Ex. gluteus maximus
Muscle names may indicate size:
Maximus: Largest
Minimus: Smallest
Vastus: Large or broad

Shape: Ex. deltoid (triangular)
A muscle may be named according to its shape, such as:
Triangular
Circular
Trapezoid

Function: Ex. Masseter
-Some muscles are named according to their main action or function. The masseter, for example, is associated with chewing.
• Muscle Belly : The belly is the thick, central, and fleshy part of a muscle. It lies between the muscle’s attachments.

Muscles of Head and Neck

Occipitofrontalis: raises eyebrows (forehead)

Orbicularis oculi: allows blinking (eyes)

Orbicularis oris: kissing muscle (mouth)

Zygomaticus: smiling muscle (cheek)

Masseter: A major muscle of mastication, or chewing.

Buccinator: Compresses the cheek and assists with actions involving the mouth, such as chewing, sucking, and blowing.

Sternocleidomastoid: Helps flex, rotate, and tilt the neck. Its name refers to its attachments to the sternum, clavicle, and mastoid process.

Trapezius: A large muscle extending across the upper back and neck. It helps move and stabilize the shoulders and is associated with the nape of the neck.

Platysma: A thin muscle at the front of the neck that helps move the lower lip and mandible and tighten the skin of the neck.




Thoracic Muscles

External intercostals:

elevate ribs for inspiration (breath in)

Internal intercostals:

depress ribs during forced expiration (breath out)

Diaphragm:
moves during quiet breathing

Abdominal Wall Muscles

Rectus abdominis:

- center of abdomen (abs)

- compresses abdomen

External abdominal oblique:

- sides of abdomen

- compresses abdomen

Internal abdominal oblique:

compresses abdomen

Transverse abdominis:

compresses abdomen



Upper Limb Muscles

Trapezius:

- shoulders and upper back

- extends neck and head

Pectoralis major: