Introduction to Muscle Physiology and Sliding Filament Theory

Vocabulary flashcards covering key terms involved in muscle types, skeletal muscle structure, excitation–contraction coupling, and the sliding filament theory.

Skeletal Muscle

Voluntary muscle type attached to bones; responsible for body movement.

Diaphragm

Skeletal muscle of respiration that contracts mostly involuntarily.

Myocardium

Cardiac (heart) muscle tissue; similar in structure to skeletal muscle.

Smooth Muscle

Involuntary muscle found in vessel walls, GI tract, uterus, etc.

Myocyte

Generic term for a muscle cell.

Myometrium

Smooth muscle layer of the uterus.

Sarcolemma

Plasma (cell) membrane of a skeletal muscle fiber.

Sarcoplasm

Cytoplasm of a muscle fiber.

Sarcoplasmic Reticulum (SR)

Specialized smooth endoplasmic reticulum in muscle cells that stores Ca²⁺.

T-Tubule (Transverse Tubule)

Invagination of the sarcolemma that conducts action potentials into the cell interior.

DHP Receptor

Voltage-sensitive protein in T-tubules that triggers opening of ryanodine channels.

Ryanodine Channel

Calcium-release channel of the SR opened via the DHP receptor.

Ligand-Gated Nicotinic Receptor

Acetylcholine-activated Na⁺ channel at the neuromuscular junction.

Somatic Motor Neuron

Neuron that voluntarily stimulates skeletal muscle fibers.

Na⁺/K⁺ Pump (Na⁺-K⁺ ATPase)

Membrane pump that maintains Na⁺ and K⁺ gradients (3 Na⁺ out / 2 K⁺ in).

SERCA (Ca²⁺ ATPase)

Pump that returns Ca²⁺ to the SR against its gradient using ATP.

Sarcomere

Contractile unit of muscle between two Z-discs.

Z-Disc

Boundary structure anchoring thin filaments at each end of a sarcomere.

Thin Filament

Filament composed of F-actin, tropomyosin, and troponin.

G-Actin

Globular actin monomer bearing the myosin-binding site.

F-Actin

Filamentous actin strand formed by polymerized G-actin.

Thick Filament

Filament consisting of bundled myosin molecules with protruding heads.

Myosin Head

Motor domain of myosin that binds actin and hydrolyzes ATP.

Tropomyosin

Regulatory protein that blocks myosin-binding sites on actin at rest.

Troponin

Calcium-binding regulatory complex that moves tropomyosin off actin sites.

H Zone

Central region of a sarcomere containing only thick filaments; narrows during contraction.

Crossbridge

Attachment of a myosin head to actin during contraction.

Power Stroke

Pivot of the myosin head that pulls thin filaments inward, shortening the sarcomere.

Rigor State

Phase where myosin remains bound to actin after the power stroke until ATP binds.

Rigor Mortis

Post-mortem stiffening due to absence of ATP preventing crossbridge detachment.

Sliding Filament Theory

Model describing muscle contraction as sliding of thin over thick filaments powered by cyclical crossbridge activity.

Myosin ATPase

Enzymatic activity of the myosin head that hydrolyzes ATP to energize contraction.