Muscular System Vocabulary Flashcards

Comprehensive vocabulary flashcards covering skeletal, cardiac, and smooth muscle traits, sarcomere structure, excitation-contraction coupling, neuromuscular junction mechanics, contraction types, and ATP regeneration pathways.

Skeletal Muscle

A voluntary, striated muscle tissue with multinucleated cells (many nuclei per cell) responsible for the movement of bones and joints.

Cardiac Muscle

An involuntary, striated, and branching muscle tissue containing $1\text{--}2$ nuclei per cell found in heart walls to pump blood.

Smooth Muscle

An involuntary, non-striated muscle tissue with one nucleus per cell located in blood vessels and hollow visceral organs.

Excitability

The special characteristic of muscle tissue enabling it to receive and respond to a stimulus (responsiveness or irritability).

Contractility

The functional property of muscle tissue defining its ability to shorten forcibly when adequately stimulated.

Extensibility

The ability of muscle tissue to be stretched or extended without causing tissue damage.

Elasticity

The ability of muscle tissue to recoil and resume its normal resting length after being stretched.

Sarcolemma

The plasma membrane surrounding a muscle fiber (myocyte).

Skeletal Muscle Organizational Sheaths

The connective tissue layers surrounding muscle structures: epimysium surrounding the whole muscle organ, perimysium surrounding muscle fascicles, and endomysium surrounding individual myocytes.

Epimysium

An outer layer of dense connective tissue that wraps around an entire skeletal muscle organ.

Perimysium

A fibrous layer of connective tissue that groups individual muscle cells into bundles called fascicles.

Endomysium

A delicate layer of connective tissue surrounding each individual muscle fiber (myocyte).

Sarcomere

The functional contractile unit of skeletal muscle delineated by two successive Z discs, containing overlapping thick and thin myofilaments.

Myosin

The principal protein component of thick filaments, consisting of a rod-like tail, flexible hinge, and two globular heads containing actin- and ATP-binding sites.

Actin

The main protein component of thin filaments, consisting of globular G actin subunits that assemble into long fibrous F actin strands.

Tropomyosin

A regulatory polypeptide strand that spirals around actin and blocks myosin-binding sites when muscle tissue is relaxed.

Troponin

A globular three-peptide complex ($\text{TnI}$, $\text{TnT}$, $\text{TnC}$) attached to actin that moves tropomyosin away from myosin-binding sites when bound to calcium ions.

Triad

A cellular feature in skeletal muscle consisting of a central T tubule flanked on both sides by terminal cisternae of the sarcoplasmic reticulum.

Transverse Tubule (T-tubule)

An invagination of the sarcolemma that conducts electrical action potentials deep into the muscle fiber to trigger calcium release.

Neuromuscular Junction (NMJ)

The site of communication where an axonal terminus of a motor neuron meets the motor end plate of a single muscle fiber.

Motor Unit

A single somatic motor neuron along with all the individual muscle fibers it innervates.

Acetylcholine (ACh)

The neurotransmitter stored in synaptic vesicles of motor axon terminals that diffuses across the synaptic cleft to excite muscle fibers.

Depolarization

The initial electrical change in an action potential caused by rapid influx of $\text{Na}^+$ ions into the cell, making the inside of the membrane less negative.

Action Potential Phases

The electrical sequence across the sarcolemma consisting of resting potential (around $-80\text{--}-85\text{ mV}$), depolarization phase via $\text{Na}^+$ influx, repolarization phase via $\text{K}^+$ efflux, and undershoot.

Excitation-Contraction Coupling

The sequence of events connecting the propagation of an action potential along the sarcolemma and T tubules to the sliding of myofilaments via calcium release.

Sliding Filament Theory

The mechanism of muscle contraction in which myosin cross-bridges attach to actin, perform a power stroke pulling actin toward the M line, detach upon binding ATP, and cock back into a high-energy state.

Muscle Tone

A state of continuous partial contraction in skeletal muscle maintained involuntarily by alternating active motor units.

Rigor Mortis

The temporary postmortem stiffening of body muscles occurring within $2\text{--}3\text{ hours}$ after death due to complete lack of ATP required for cross-bridge detachment.

Isometric Contraction

A type of muscle contraction where muscle length remains constant while muscle tension increases without producing movement.

Isotonic Contraction

A type of muscle contraction where muscle tension remains constant as muscle length changes (shortens or lengthens) to produce movement.

Single Muscle Twitch

The mechanical response of a motor unit to a single action potential, consisting of a latent period, period of contraction, and period of relaxation.

Latent Period

The initial time delay (first few milliseconds) following stimulation during excitation-contraction coupling when muscle tension begins to build without observable movement.

Direct Phosphorylation

An immediate ATP regeneration pathway where creatine phosphate transfers a high-energy phosphate group directly to ADP, producing $1\text{ ATP}$ per creatine phosphate molecule for about $15\text{ seconds}$.

Glycolysis

An anaerobic metabolic pathway in the cytosol that breaks down glucose into pyruvic acid, yielding $2\text{ ATP}$ per glucose molecule without requiring oxygen.

Lactic Acid

An organic byproduct formed from pyruvic acid during anaerobic glycolysis when oxygen supply to contracting muscles is restricted.

Aerobic Respiration

An oxygen-requiring mitochondrial pathway that breaks down glucose or fatty acids to produce $32\text{ ATP}$ molecules along with $\text{CO}_2$ and $\text{H}_2\text{O}$.

Muscle Fatigue

A state of physiological inability of a muscle to contract despite receiving continued nervous stimulation.

Oxygen Deficit

The extra volume of oxygen the body must take in post-exercise to restore oxygen reserves, re-synthesize ATP and creatine phosphate, and convert accumulated lactic acid.