Muscular System Anatomy, Physiology, and Disorders

Vocabulary flashcards covering skeletal muscle anatomy, sliding filament theory, energy metabolism, types of contractions, body movements, and muscular disorders.

Skeletal Muscle

A type of striated muscle under conscious control that moves bones.

Smooth Muscle

An involuntary, non-striated muscle found in organs that moves substances inside the body without conscious control.

Cardiac Muscle

A striated, involuntary muscle found only in the heart that pumps blood.

Epimysium

The outer connective tissue covering that surrounds a skeletal muscle.

Perimysium

The connective tissue partitions within a skeletal muscle that group fibers into bundles.

Fascicle

A bundle of muscle cells (fibers) within a muscle.

Muscle Fibers

Individual muscle cells that contain smaller myofibrils.

Myofibrils

Thin fibers inside a muscle cell containing actin and myosin filaments that enable contraction.

I Band

The light region of striated muscle tissue composed of actin filaments.

A Band

The dark region of striated muscle tissue composed of myosin filaments.

Z Line

Vertical bands marking the boundaries of individual sarcomeres in striated muscle.

Sarcomere

The contractile unit of a muscle fiber, defined as the area between two Z lines.

Origin

The point of attachment of a muscle to the less mobile bone.

Insertion

The point of attachment of a muscle to the more moveable bone.

Neuromuscular Junction

The space between a nerve and a muscle cell where chemical communication occurs.

Acetylcholine

A neurotransmitter that diffuses from motor end plates across the neuromuscular junction to the sarcolemma to signal muscle contraction.

Acetylcholinesterase

An enzyme that destroys and clears acetylcholine from the neuromuscular junction.

Sliding Filament Theory

The mechanism of contraction where actin and myosin filaments slide past each other, shortening the muscle following calcium release and cross-bridge attachment.

Isotonic Contraction

A type of muscle contraction in which the muscle changes its length.

Isometric Contraction

A contraction where the muscle creates force without changing its length, such as holding a plank.

Concentric Contraction

A subtype of isotonic contraction where the muscle shortens while producing force, such as lifting a dumbbell.

Eccentric Contraction

A subtype of isotonic contraction where the muscle lengthens while controlling a movement, such as slowly lowering a dumbbell.

Antagonistic Muscles

Muscles that work against each other to produce opposing movements.

Synergistic Muscles

Muscles that work together to perform or stabilize a common movement.

Flexion

A movement that reduces the angle of a joint, such as bending the elbow.

Extension

A movement that increases the angle of a joint, such as straightening the knee.

Rotation

The movement of a body part around a plane or central axis, such as turning the head from side to side.

Abduction

Movement of a body part away from the midline of the body.

Adduction

Movement of a body part toward the midline of the body.

Dorsiflexion and Plantar Flexion

Special movements involving the upward (dorsiflexion) and downward (plantar flexion) motion of the foot.

Inversion and Eversion

Special movements of the foot turning inward toward the midline (inversion) or outward away from the midline (eversion).

Pronation and Supination

Rotational movements of the lower arm where the thumb turns down (pronation) or up (supination).

Opposition

The specialized movement of the thumb touching the fingertips of the same hand.

Flaccidity

A condition marked by soft, weak muscles and a temporary loss of muscle tone.

Atrophy

A condition characterized by a long-term loss of muscle control or tone, causing muscles to become smaller and weaker.

Muscular Dystrophy

A genetic disorder causing progressive muscle weakness (often inferior to superior) due to changes in muscle proteins; managed with physical therapy, heat, exercise, supportive devices, or steroids.

Myasthenia Gravis

An autoimmune breakdown in communication between nerves and muscles targeting acetylcholine receptors, leading to loss of muscle control; treated with oral or IV medications.

Tetanus

A muscular disorder associated with the loss of acetylcholinesterase ($\text{ACHE}$), resulting in sustained muscle contractions.

Low Energy Demand Metabolism

Cellular respiration using oxygen to convert sugar into energy: $\text{sugar (fuel)} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{energy} \rightarrow \text{ATP}$.

High Energy Demand Metabolism

Anaerobic pathway where reserve $\text{ATP}$ is rapidly used; cells utilize creatine phosphate ($\text{ADP} + \text{CP} \rightarrow \text{ATP}$) and glycogen ($\text{glycogen} \rightarrow \text{lactic acid} + \text{energy}$), leading to lactic acid buildup, oxygen debt, fatigue, and soreness.