Skeletal Muscle Structure and Function

Comprehensive vocabulary flashcards covering the structural hierarchy, cellular components, sarcomere zones, contractile mechanism, neuromuscular junction, and functional muscle roles from the lecture notes.

Epimysium

The connective tissue layer that surrounds the whole (entire) muscle.

Fascicle

A bundle of muscle fibers surrounded by perimysium.

Perimysium

The connective tissue layer that surrounds a fascicle (muscle fiber bundle).

Muscle fiber

One long, cylindrical muscle cell surrounded by endomysium, featuring multiple nuclei and a striped (striated) appearance.

Endomysium

The connective tissue layer that surrounds each individual muscle fiber.

Myofibril

A thread-like structure inside a muscle fiber containing contractile proteins and repeating sarcomeres.

Sarcomere

The basic functional contractile unit of a muscle fiber containing actin and myosin, running from one Z disc to the next.

Sarcolemma

The cell membrane of a muscle fiber.

Sarcoplasm

The cytoplasm located inside a muscle fiber.

Sarcoplasmic reticulum (SR)

A cellular structure that stores and releases calcium ions ($Ca^{2+}$), which help trigger contraction.

Thick filament

The muscle filament composed of myosin; its heads attach to actin and pull during contraction.

Thin filament

The muscle filament composed of actin, along with the regulatory proteins troponin and tropomyosin.

Troponin

A regulatory protein on the thin filament that binds calcium, causing tropomyosin to shift out of the way.

Tropomyosin

A regulatory protein that blocks active sites on actin when the muscle is in a relaxed state.

Z disc (Z line)

A boundary structure marking each end of a sarcomere where thin filaments anchor.

A band

The dark band that spans the full length of the thick myosin filaments (including overlap with actin) and remains the same length during contraction.

I band

The light band containing thin filaments without thick-filament overlap; it shortens (gets smaller) during contraction.

H zone

The middle region of the A band consisting of thick filaments without thin-filament overlap; it gets smaller during contraction.

M line

The center line of the sarcomere situated directly in the middle of the H zone.

Neuromuscular junction (NMJ)

The synapse formed between a motor neuron and a skeletal muscle fiber.

Acetylcholine (ACh)

The neurotransmitter released by a motor neuron that stimulates a skeletal muscle fiber and initiates contraction.

Agonist (prime mover)

The main muscle responsible for producing a specific movement, such as the biceps during elbow flexion.

Antagonist

A muscle that opposes or reverses the agonist's movement and often relaxes while the agonist contracts, such as the triceps during a biceps curl.

Synergist

A muscle that assists the prime mover by adding force or stabilizing a joint, such as the brachialis and brachioradialis during elbow flexion.

Fixator

A muscle that stabilizes one body part so another part can move effectively, such as shoulder or back muscles during a biceps curl.