Lecture 3: Muscular System

Biomedicine

Human Sciences - A field of study focused on the application of biological and physiological principles to clinical practice.

Muscular System

The organ system that enables humans and other animals to move using the muscular and skeletal systems.

Types of Muscles

The three types of muscles in the human body are skeletal, cardiac, and smooth muscles.

Striated Muscle

Muscle tissue that has a striped appearance under a microscope, including skeletal and cardiac muscles.

Non-Striated Muscle

Muscle tissue that does not have a striped appearance, such as smooth muscle.

Skeletal Muscle

A type of striated muscle that is under voluntary control and is responsible for movement at joints.

Smooth Muscle

an involuntary, non-striated muscle found in blood vessels, airways, hollow organs, the iris, and skin. It changes tissue diameter, shape, or orientation under autonomic nervous system control. Its small, single-nucleus cells contract by pulling dense bodies closer, causing a twisting motion. Contraction can also be triggered by hormones, signals, or chemical agents..

Muscle Functions

includes movement, maintaining posture, heat production, storage of substances, and movement of substances.

Contractility

The ability of muscle tissue to contract or shorten.

Excitability

The ability of muscle tissue to respond to stimuli, such as nerve impulses.

Extensibility

The ability of muscle tissue to stretch without being damaged.

Elasticity

The ability of muscle tissue to return to its original length and shape after contraction or extension.

Sarcomere

The basic unit of striated muscle tissue, consisting of actin and myosin filaments.

Myofibrils

Cylindrical structures within muscle fibers made of bundles of protein filaments that are contractile.

Myofilaments

The smaller filaments within myofibrils, including actin (thin) and myosin (thick) filaments.

Neuromuscular Junction (NMJ)

The synapse where motor neurons meet muscle fibers, facilitating muscle contraction.

Sliding Filament Model

A theory explaining muscle contraction through the sliding of actin and myosin filaments over each other.

Muscle Hypertrophy

The increase in muscle size due to strength training and hormonal influences. It refers to muscle growth, supported by essential minerals like calcium, magnesium, and potassium, and promoted by hormones such as growth hormone, testosterone, and thyroid hormones. Strength training increases muscle breakdown, requiring protein for repair and growth.

Aerobic Respiration

A process that requires oxygen to produce ATP, occurring in the mitochondria.

Anaerobic Respiration

A process that occurs without oxygen, producing ATP and lactic acid, typically during intense exercise.

Creatine Phosphate

An energy storage form in muscles that provides a quick source of energy during short bursts of activity.

Muscle Fatigue

a condition that results from overuse, poor posture, or repetitive activity, leading to energy depletion and lactic acid buildup. To prevent this, maintain good posture, rest muscles, and consider recovery methods like yoga, relaxation, and proper nutrition.

Impingement Syndrome

a shoulder condition where movement causes pain and limited mobility due to inflammation or damage to the rotator cuff tendons or bursa, typically in the sub-acromial space. Causes include overuse, aging, poor posture, bone spurs. Symptoms include shoulder ache, pain with certain movements, a catching sensation, and weakness. Treatment may involve cortisone injections, NSAIDs, or surgery.

Fibromyalgia

a chronic pain disorder marked by widespread musculoskeletal pain, fatigue, and symptoms like anxiety and sleep disturbances. It involves abnormal pain processing in the central nervous system, leading to increased pain sensitivity. Common in women aged 30-50, it may be linked to factors like stress, toxins, and neurotransmitter imbalances. Treatment often includes medications, especially antidepressants.

Myasthenia Gravis

an autoimmune disease causing muscle weakness due to antibodies blocking acetylcholine receptors at the neuromuscular junction. It mainly affects the face and neck muscles, leading to symptoms like double vision, ptosis, and difficulty with speech and swallowing. Treatment includes acetylcholinesterase inhibitors, corticosteroids, and in severe cases, plasma exchange.

Movement

a result of muscular contraction. This relies on the integrated functioning of the muscles, bones and joints

Maintaining posture

stabilising joints, posture and balance through continued partial muscle contraction.

Heat production

thermogenesis. Helps maintain normal body temperature (36.5‒37.5°C). Shivering describes involuntary contractions of skeletal muscles.

fascia

a dense sheet of connective tissue that organises muscle, secures it to skin, and provides stability. Collagen is a major component.

sarcolemma

The cell membrane of a skeletal muscle fibre

sarcoplasm

the cytoplasm of a muscle fiber and cell, containing the organelles, myofibrils, and the components necessary for muscle contraction, such as glycogen, myoglobin, and enzymes.

transverse tubules

extend from the cell membrane into the muscle cells.

sarcoplasmic reticulum

stores calcium needed for muscle contraction.

myoglobin

red coloured, iron and oxygenbinding protein

myoblasts

Muscle fibres are formed from the fusion of these cells in the embryo.

myocytes

mature muscle cells - can no longer undergo mitosis

satellite cells

limited regenerative capacity

Actin

thin filaments

Myosin

(thick filaments) — shaped like golf clubs; the ‘myosin heads’ can bind to actin.

sarcomeres

A sarcomere is the basic unit of striated muscle, formed by overlapping actin and myosin filaments. It includes the H zone (myosin only), the A band (overlap of actin and myosin), the I band (actin only), and Z discs, which mark its boundaries.

Connective Tissue

It surrounds and binds muscle fibers, forming layers like the endomysium (around fibers), perimysium (around bundles of fibers), and epimysium (around the whole muscle). It strengthens connections and helps transfer force to tendons and fascia.

Skeletal Muscle Hierarchy

Myofibrils (made of actin and myosin) form myocytes, which bundle into fascicles surrounded by the perimysium. Fascicles combine to form the whole muscle, enclosed by the epimysium, which attaches to bone.

Neuromuscular Junction (NMJ)

where a motor neuron meets a muscle fiber. The neuron releases acetylcholine, which triggers a muscle impulse along the sarcolemma. Muscle contraction strength is influenced by the number and frequency of motor neuron impulses.

Sliding Filament: Contraction

A nerve impulse triggers calcium release in the muscle cell, enabling myosin to bind to actin. Using ATP, the filaments slide past each other, shortening the muscle fiber.

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Sliding Filament: Relaxation

When nerve stimulation stops, calcium is pumped back into storage using magnesium and ATP, breaking the bond between actin and myosin. The filaments return to their starting positions, lengthening the muscle fiber and causing relaxation.

Muscle Metabolism

It requires large amounts of ATP, produced from nutrients like glucose, fatty acids, and amino acids, with oxygen enhancing production. A rich blood supply is essential, and ATP is generated through two main pathways.

White muscle fibers

They are large-diameter fibers with low myoglobin content, relying on anaerobic respiration for fast, strenuous work, but they fatigue quickly.

Red muscle fibers

They are small-diameter fibers with high myoglobin content, relying on aerobic respiration and containing many mitochondria, making them suited for sustained activity without fatigue.

Slow oxidative fibers (SO)

These fibers are a type of red muscle fiber characterized by high endurance, utilizing aerobic respiration for energy, and are resistant to fatigue.

Fast oxidativeglycolytic fibers (FOG):

These fibers are a type of muscle fiber that possess characteristics of both fast-twitch and slow-twitch fibers, enabling them to perform well in both anaerobic and aerobic activities. They have moderate endurance and a high capacity for both power and fatigue resistance.

Fast glycolytic fibers (FG):

_{These fibers are a type of muscle fiber that primarily rely on anaerobic metabolism for energy, providing high power output but low endurance, making them suited for short bursts of intense activity.}

Occipitofrontalis

A muscle that covers the forehead and the back of the skull, responsible for raising the eyebrows and wrinkling the forehead.

Orbicularis oculi

A circular muscle around the eye that enables blinking and closing the eyelids.

Orbicularis oris

A circular muscle around the mouth that controls movements of the lips, enabling actions such as puckering and closing the lips.

Masseter

A thick, powerful muscle located at the jaw, primarily responsible for elevating the mandible during chewing.

Temporalis

A muscle located on the side of the head, it plays a key role in elevating and retracting the mandible during chewing.

Sternocleidomastoid

A prominent muscle in the neck that allows for rotation and flexion of the head, turning and tilting.

Trapezius

Pulls head backwards. Elevates (shrugs) and retracts shoulders.

Supraspinatus

A muscle located in the shoulder that is part of the rotator cuff, responsible for abducting the arm and stabilizing the shoulder joint.

Psoas

A major hip flexor muscle located in the lower back, responsible for flexing the thigh towards the body and trunk and stabilizing the lumbar spine.

Latissimus dorsi

A large muscle in the back that extends, adducts, and rotates the arm. It plays a key role in movements such as pulling and lifting.

Quadratus lumborum

A muscle of the lower back that helps stabilize the pelvis and lumbar spine, as well as facilitating lateral flexion of the spine. Bending backwards or sideways

Erector spinae

A group of muscles that extend the spine and maintain posture. They are crucial for movements such as bending and twisting the back.

Pectoralis major

Rectus abdominis

A long muscle in the front of the abdomen that helps flex the spine and stabilize the pelvis. It is commonly known as the "abs" and plays a key role in core strength. It helps with bending forwards (crunches)

Internal and external obliques

Muscles located on the sides of the abdomen that assist in trunk rotation and lateral flexion. They play a significant role in core stability and support movements such as twisting and bending.

The respiratory diaphragm

It attaches to the lower ribs, sternum, and lumbar spine. When it contracts, it moves downward, expanding lung space for air. Vital structures, like the aorta and oesophagus, pass through it.

Deltoid

A triangular muscle located on the shoulder that is responsible for arm abduction, flexion, and extension. It is crucial for lifting the arm and stabilizing the shoulder joint.

Biceps brachii

A muscle on the front of the upper arm that flexes the elbow and rotates the forearm

Triceps brachii

A muscle located at the back of the upper arm that extends the elbow and arm adduction (moving arm towards the midline, lowering arm)

Flexor carpi muscle

Flexes the hand at the wrist joint.

Extensor carpi muscle

Extends the hand at the wrist joint.

Gluteus maximus

a muscle that helps rotate, abduct and extend the hip outward. Attaches from the ilium (pelvis) to the femur.

Piriformis

Externally rotates hips. Attaches from the sacrum to the femur

Hamstring

Bends knee (flexes knee). Three separate muscles in the posterior thigh.

Rectus femoris

Flexes hip and extends knee (e.g. kicking a football).(One of four quadricep muscles) Attaches from the pelvis to the tibia

Thigh adductors

Squeezes the thighs together. Attach from the pubis to the femur.

Tibialis anterior

muscle that connects the tibia to the metatarsals. It allows for dorsiflexion (lifting the foot upward) and inversion (turning the foot inward) while also supporting the foot's medial arch.

Soleus

Attaches from the posterior tibia and fibula to the calcaneum (heel bone)._{It is a powerful muscle that aids in plantarflexion of the foot, playing a key role in walking, running, and maintaining balance.}

Gastrocnemius

A major calf muscle that connects the femur to the heel bone. It assists in plantarflexion of the foot and flexes leg at the knee.

Skeletal Muscle Mechanics

involve tendons attaching muscles to bone, allowing movement at joints when muscles contract, pulling on tendons. Muscles work in pairs (e.g., biceps and triceps), with one acting as the prime mover and the other as the antagonist. Muscles can also function as synergists or fixators to support movement.

synergist

assists the prime mover in its action, e.g. when flexing the elbow, brachialis helps the biceps by pulling the ulna towards the humerus.

fixator

a muscle that keeps the origin bone stable while a prime mover contracts, e.g. in the shoulder

Cardiac Muscle

a specialized, involuntary muscle found only in the heart. Its striated fibers connect through intercalated discs for synchronized, wave-like contractions. It is autorhythmic, contracting about 75 times per minute at rest, and relies on aerobic respiration with abundant mitochondria to sustain prolonged contractions. Branching cells allow efficient contraction spread.

Smooth Muscle Properties

it contracts more slowly and for longer than skeletal muscle, with greater ability to stretch and shorten. It enables organs like the stomach and bladder to expand and contract as needed, maintains partial contraction for blood pressure, and responds to the autonomic nervous system, hormones, stretch, and blood gases.

muscle regeneration

Muscle regeneration varies by type:

• Skeletal muscle: Limited regeneration through satellite cells.

• Smooth muscle: Can increase in number (hyperplasia) and regenerate from stem cells.

• Cardiac muscle: Scarring occurs after heart attacks, but stem cells can divide. Hypertrophy can be physiological or pathological.

Homeostasis

he body's ability to maintain stable internal conditions despite external changes. Different body systems contribute to homeostasis in various ways

Muscle Tissue

plays a vital role in homeostasis by producing movement, stabilizing body position, and moving substances within the body. It also generates heat, which helps regulate body temperature.

Homeostasis: Integumentary System (skin)

contributes by facilitating facial expression and increasing blood flow to the skin through muscle activity, which helps with temperature regulation.

Homeostasis: Skeletal System

supports homeostasis by enabling movement and providing stability to joints, ensuring proper body posture and function.

Homeostasis: Nervous System

helps with homeostasis by triggering shivering, which generates heat to raise body temperature when needed.

Homeostasis: Endocrine System

influenced by exercise, which improves hormone function, such as the action of insulin. Additionally, muscles protect endocrine glands, ensuring proper hormonal balance.

homeostasis: Lymphatic System

supported by muscle activity, which helps protect lymph nodes and vessels while promoting lymph flow. Exercise can also influence the immune response, either increasing or decreasing it.

homeostasis: Respiratory System

relies on respiratory muscles to facilitate airflow in and out of the lungs. Smooth muscle adjusts the size of the airways, and skeletal muscle in the larynx controls airflow, which also affects the voice. Coughing and sneezing help clear the airways, and regular exercise improves breathing efficiency.

homeostasis: Digestive System

benefits from skeletal muscles that protect and support digestive organs, as well as muscles involved in chewing and swallowing. Smooth muscle sphincters control the flow of substances through the digestive tract, while smooth muscle in the intestinal wall helps mix contents, aiding in digestion through peristalsis.

homeostasis: Urinary System

relies on bladder muscles that control the release of urine, contributing to the regulation of body fluids and waste removal.

homeostasis: Reproductive System

depends on skeletal and smooth muscle contractions to eject semen, propel eggs along the uterine tubes, control menstrual flow, and expel a baby during childbirth.

muscle shortening

occurs when a muscle contracts and becomes shorter in length, typically as the actin and myosin filaments slide past each other. This process generates force, allowing the muscle to produce movement or maintain tension.

Muscle Strain

occurs when muscle fibers or tendons are overstretched, typically from a joint moving beyond its normal range, but the muscle remains intact and heals with proper blood supply.Treatment includes RICE (rest, ice, compression, elevation),