Muscle Tissue and the Physiology of Contraction: every key term you need (+ practice quiz)
25 flashcard terms for Anatomy & Physiology I Topic 7, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
A single skeletal muscle cell, formed by fusion of embryonic precursors so that it is long, cylindrical and holds many nuclei pressed against the cell membrane. Its cytoplasm is packed with contractile rods.
Sarcolemma
The plasma membrane of a muscle fiber. It is electrically excitable, propagates the action potential over the surface, and dips inward as tubules that carry the signal into the interior of the cell.
Myofibril
A rodlike bundle of contractile filaments running the length of a muscle fiber and occupying most of its volume. Alignment of the repeating pattern in adjacent myofibrils produces visible striations.
Sarcomere
The contractile unit of striated muscle, extending from one boundary disc to the next. Its overlapping thick and thin filaments shorten the unit during contraction, and thousands in series shorten the fiber.
Thick filament
The filament built from bundled motor proteins whose hinged heads project outward in a spiral. Each head binds the thin filament, binds and splits adenosine triphosphate, and pivots to generate force.
Thin filament
The filament built from two twisted strands of globular subunits, each bearing a binding site for a motor head, together with the regulatory proteins that cover or expose those sites.
Tropomyosin
A rope-like regulatory protein lying in the groove of the thin filament. At rest it physically blocks the binding sites, preventing the motor heads from attaching and keeping the fiber relaxed.
Troponin
A three-part regulatory complex on the thin filament. One subunit binds calcium, and that binding changes the complex shape so that the blocking protein is dragged aside and binding sites are exposed.
Sliding filament model
The explanation that muscle shortens not because filaments shorten but because thin filaments are pulled toward the center of each unit, increasing overlap while filament lengths remain constant.
Transverse tubule
An inward extension of the muscle cell membrane that penetrates deep into the fiber alongside the calcium store. It carries the surface electrical signal inward so all myofibrils are activated together.
Sarcoplasmic reticulum
The specialized smooth membrane network surrounding each myofibril that stores calcium at high concentration and releases it into the cytosol when the electrical signal arrives along the tubule.
Neuromuscular junction
The synapse where a motor neuron terminal meets a muscle fiber. Vesicles release acetylcholine into a narrow cleft, and receptors on the folded muscle membrane open cation channels that depolarize it.
Acetylcholinesterase
The enzyme in the synaptic cleft that rapidly degrades released acetylcholine. Its action ends receptor stimulation so a single nerve impulse produces a single muscle response rather than sustained firing.
Excitation contraction coupling
The sequence linking the muscle surface action potential to force production: the signal travels inward along tubules, triggers calcium release, calcium binds the regulatory complex, and cross bridge cycling begins.
Cross bridge cycle
The repeating sequence of head attachment to the thin filament, the power stroke that pivots the head and slides the filament, detachment when a fresh energy molecule binds, and re-cocking as that molecule is split.
Rigor mortis
The postmortem stiffening that follows when energy supply fails. Calcium leaks into the cytosol and exposes binding sites, but without fresh energy molecules the motor heads cannot detach from the thin filaments.
Motor unit
One motor neuron together with all the muscle fibers it innervates. Small units of a few fibers permit fine control in the eye and hand, while large units of hundreds serve powerful postural muscles.
Recruitment
The graded activation of additional motor units to increase whole muscle force. Small, easily excited units fire first and larger units join as stimulus strength rises, producing smoothly increasing tension.
Muscle twitch
The response of a fiber or motor unit to a single stimulus, comprising a latent period before tension appears, a contraction phase as force develops, and a relaxation phase as calcium is pumped back into storage.
Wave summation and tetanus
The rise in force when stimuli arrive before relaxation is complete, because calcium accumulates in the cytosol. Rapid enough stimulation fuses the individual responses into a smooth sustained contraction.
Isometric and isotonic contraction
Two loading conditions. In isometric contraction tension rises but the muscle length is unchanged because the load exceeds the force; in isotonic contraction tension is sufficient and the muscle shortens or lengthens.
Creatine phosphate
The immediate energy reserve of muscle. Its high-energy bond is transferred to regenerate the cellular energy molecule within seconds, covering the first stretch of intense effort before other pathways respond.
Oxygen debt
The extra oxygen consumed after exercise to restore resting conditions: replenishing the immediate energy reserve and oxygen bound to muscle pigment, converting accumulated lactate and repaying borrowed capacity.
Slow oxidative and fast glycolytic fibers
Contrasting fiber types. Slow oxidative fibers are small, capillary-rich and fatigue resistant for posture and endurance; fast glycolytic fibers are large, pale and powerful but tire quickly.
Smooth muscle
Nonstriated involuntary muscle of hollow organs, with single central nuclei, filaments anchored to dense bodies rather than aligned units, slow economical contraction and the capacity to stretch without losing tone.