muscular system physiology

Functions of Muscles

Muscles enable body movement, maintain posture through muscle tone, produce body heat as a byproduct of metabolism, and facilitate communication through facial expressions and speech.

Contractility

The ability of muscle tissue to shorten forcefully when stimulated.

Excitability

The ability of muscle tissue to respond to electrical stimuli.

Extensibility

The ability of muscle tissue to stretch beyond resting length without damage.

Elasticity

The ability of muscle tissue to return to original resting length after being stretched or contracted.

Muscle Contraction

It is initiated at the neuromuscular junction where a motor neuron releases acetylcholine, triggering an action potential that causes the release of calcium from the sarcoplasmic reticulum.

Sliding Filament Theory

The mechanism where calcium binds to troponin, moving tropomyosin away from binding sites on actin, allowing myosin heads to form cross-bridges and pull actin filaments toward the center of the sarcomere.

Isometric Contractions

Contractions where the muscle generates tension without changing length.

Isotonic Contractions

Contractions that involve a change in muscle length.

Incomplete Tetanus

Occurs with frequent stimulation and partial relaxation in between muscle twitches.

Complete Tetanus

Occurs with rapid stimulation resulting in sustained maximum tension with no relaxation.

Skeletal Muscle

Striated, voluntary muscle that is multi-nucleated.

Smooth Muscle

Non-striated, involuntary muscle, spindle-shaped, found in hollow organs; contraction involves calmodulin and dense bodies instead of sarcomeres.

Cardiac Muscle

Striated, involuntary muscle located in the heart, characterized by intercalated discs that allow rapid electrical flow between cells.

Paralysis

A condition characterized by the loss of muscle function in one or more muscle groups, often due to disruption of nerve pathways or toxins.

Myasthenia Gravis

An autoimmune disorder that leads to the destruction of acetylcholine receptors, causing weakness in voluntary muscles.

Duchenne Muscular Dystrophy

A genetic mutation that results in the lack of dystrophin, leading to progressive muscle wasting and weakness, primarily affecting boys.

fascia

a strong, fibrous sheet of connective tissue made mostly of collagen that wraps around, supports, and separates skeletal muscles, bones, and internal organs

epimysium

The outer layer of deep fascia that surrounds an entire skeletal muscle.

perimysium

A middle layer that divides the muscle into smaller bundles of fibers called fascicles

endomysium

The innermost layer that surrounds each individual muscle cell or fiber.

Relaxation

When stimulation stops, calcium is actively transported back into the sarcoplasmic reticulum, allowing tropomyosin to block actin binding sites once again.

Nerve Impulse

Motor neurons release acetylcholine into the synaptic cleft, triggering an action potential in the muscle fiber.

Calcium Release

The action potential travels through T-tubules, signaling the sarcoplasmic reticulum to release calcium.

Crossbridge Cycling

Calcium binds to troponin, moving tropomyosin to expose actin binding sites. Myosin heads then bind to actin, utilizing ATP to pull filaments and shorten the sarcomere

Type 1 (slow twitch oxidative)

reddish, high endurance, used for posture

Type 2 (fast twitch)

Divided into 2A and 2B, these are generally paler, optimized for rapid, intense movent