Muscular System Histology And Physiology

Comprehensive vocabulary flashcards covering the histology, anatomy, and physiological processes of the muscular system based on Chapter 09.

Skeletal Muscle

A voluntary muscle tissue controlled by the nervous system, responsible for locomotion, facial expressions, and posture; characterized by very long, cylindrical, striated cells ($1\,mm$ to $4\,cm$ average length).

Smooth Muscle

Involuntary muscle located in the walls of hollow organs, blood vessels, and glands; cells are spindle-shaped ($15$ to $200\,\mu m$ in length) and lack striations.

Cardiac Muscle

An involuntary, autorhythmic muscle found only in the heart; cells are cylindrical and branched, containing intercalated disks and striations.

Contractility

The ability of a muscle to shorten with force.

Excitability

The capacity of a muscle to respond to a stimulus, which is usually from nerves.

Extensibility

The property that allows a muscle to be stretched beyond its normal resting length and still be able to contract.

Elasticity

The ability of a muscle to recoil to its original resting length after being stretched.

Epimysium

The connective tissue layer that surrounds an entire muscle containing many fascicles.

Perimysium

Loose connective tissue that surrounds a group of muscle fibers, which are collectively called a fascicle.

Endomysium

Loose connective tissue that separates individual muscle fibers within each fascicle.

Fascicles

Bundles of muscle cells surrounded by perimysium.

Hypertrophy

An increase in muscle size due to the enlargement of individual muscle fibers, rather than an increase in the number of fibers.

Sarcolemma

The plasma membrane of a muscle fiber.

Transverse tubules (T tubules)

Inward folds of the sarcolemma that project into the interior of the muscle cell to carry action potentials.

Sarcoplasmic reticulum (SR)

A specialized smooth endoplasmic reticulum in muscle cells that stores calcium ions ($Ca^{2+}$).

Triad

A structure formed by two terminal cisternae of the sarcoplasmic reticulum and their associated T tubule.

Sarcomere

The basic functional unit of a muscle fiber and the smallest part that can contract; it is the region between two Z disks.

Z disk

A filamentous network of protein that serves as the attachment site for actin myofilaments.

A band

The central dark-staining region of a sarcomere consisting of overlapping actin and myosin myofilaments.

I band

Lighter-staining regions of the sarcomere that contain Z disks and consist only of actin myofilaments.

H zone

The region in the center of the A band where only myosin is present and actin filaments do not overlap.

Tropomyosin

An elongated protein that winds along the F actin double helix, regulating the interaction between actin and myosin by covering active sites.

Troponin

A protein composed of three subunits: one binds to actin, a second to tropomyosin, and a third to calcium ions ($Ca^{2+}$).

Neuromuscular Junction (Synapse)

The point of contact between a motor neuron and a muscle fiber where chemical communication occurs.

Acetylcholine (ACh)

The neurotransmitter contained within synaptic vesicles that is released to stimulate muscle fiber action potentials.

Sliding Filament Model

The mechanism where actin myofilaments slide over myosin myofilaments to shorten the sarcomere without the filaments changing length.

Depolarization

The phase of an action potential where the inside of the plasma membrane becomes less negative, typically triggered by the entry of $Na^{+}$.

Repolarization

The return of the membrane to its resting potential, occurs when $Na^{+}$ channels close and $K^{+}$ channels open.

Excitation-Contraction Coupling

The process linking electrical signals (action potentials) on the sarcolemma to mechanical contraction via calcium release.

Power Stroke

The movement of the myosin head at its hinge region while bound to actin, pulling the actin filament toward the H zone.

Muscle Twitch

The response of a single muscle fiber to a single action potential, consisting of lag, contraction, and relaxation phases.

Isometric Contraction

A type of contraction where muscle tension increases but the muscle length does not change, common in postural muscles.

Isotonic Contraction

A type of contraction where the muscle length changes (shortens or lengthens) while the tension remains constant.

Motor Unit

A single motor neuron and all the specific muscle fibers it innervates.

Treppe

A graded increase in contraction force seen when a muscle is stimulated repeatedly after full relaxation between stimuli.

Incomplete Tetanus

A condition where muscle fibers partially relax between contractions due to increasing frequency of stimulation.

Complete Tetanus

A sustained contraction without any relaxation between stimuli caused by high-frequency action potentials.

Slow-twitch (Type I) Fibers

Fatigue-resistant fibers that contract slowly, have a rich blood supply, and contain large amounts of myoglobin; often called 'dark meat'.

Fast-twitch (Type II) Fibers

Fibers that respond rapidly to stimulation with myosin that breaks down ATP quickly; they have less blood supply and fewer mitochondria than Type I.

Creatine Kinase

An enzyme that facilitates the transfer of phosphate from creatine phosphate to ADP to quickly generate ATP.

Oxygen Debt

The lag time between the start of exercise and the onset of heavy breathing, representing the oxygen needed to restore homeostasis.

Calmodulin

A calcium-binding protein in smooth muscle that regulates myosin kinase to initiate contraction.

Intercalated Disks

Specialized cell-to-cell attachments in cardiac muscle that contain gap junctions for synchronized contraction.