Muscular System Anatomy and Physiology Flashcards

Epimysium

The layer of connective tissue surrounding the entire skeletal muscle that protects it and helps transmit contractile force.

Perimysium

The connective tissue sheath surrounding each muscle fascicle that organizes muscle fibers into distinct bundles.

Endomysium

The delicate connective tissue layer surrounding each individual skeletal muscle fiber.

Sarcomere

The basic functional and contractile unit of a myofibril in skeletal and cardiac muscle, bounded on each end by a Z disc.

Cardiac Muscle Tissue

Involuntary, striated muscle tissue found in the heart wall (myocardium), characterized by short, branched fibers and intercalated discs.

Smooth Muscle Tissue

Involuntary, non-striated muscle tissue composed of spindle-shaped (fusiform) cells with a single centrally located nucleus, found in the walls of hollow organs.

Intercalated Discs

Specialized microscopic structures present in cardiac muscle that connect adjacent muscle fibers and facilitate synchronized rhythmic contraction.

A Band

The dark band of a sarcomere that spans the entire length of thick myofilaments (myosin).

I Band

The light band of a sarcomere containing only thin myofilaments (actin) without overlap from thick filaments.

H Zone

The central region of the A band in a relaxed sarcomere that contains thick filaments (myosin) but no thin filaments.

M Line

A protein structure located at the exact center of the sarcomere that holds and stabilizes adjacent thick filaments.

Sarcoplasmic Reticulum

A specialized membrane system surrounding myofibrils that stores and releases calcium ions ($Ca^{2+}$) required for muscle contraction.

Transverse Tubules (T-tubules)

Deep inward extensions of the sarcolemma that conduct electrical action potentials rapidly into the interior of the muscle fiber.

Acetylcholine (ACh)

The neurotransmitter released by somatic motor neurons at the neuromuscular junction to induce muscle fiber depolarization.

Troponin

A regulatory protein on the thin filament that binds calcium ions ($Ca^{2+}$), triggering a shape change that shifts tropomyosin away from actin binding sites.