Microscopic Anatomy and Organization of Skeletal Muscle

These flashcards cover key vocabulary related to the microscopic anatomy and organization of skeletal muscle.

Muscle fiber

A large, long cylindrical cell that is the basic structural unit of skeletal muscle.

Myofibril

Rod-shaped organelles found in muscle fibers, composed of myofilaments and responsible for muscle contraction.

Myofilament

Threadlike structures within myofibrils, primarily composed of actin (thin) and myosin (thick) filaments.

Sarcomere

The contractile unit of a myofibril, defined by the region between two Z discs.

T tubules

Transverse tubules are indents of the sarcolemma that run deep into muscle fibers and facilitate the transmission of action potentials.

Terminal cisterns

Enlarged areas of the sarcoplasmic reticulum that are located adjacent to T tubules and help release calcium ions for contraction.

Endomysium

A delicate connective tissue sheath that surrounds each muscle fiber.

Perimysium

A collagenic membrane that surrounds groups of muscle fibers to form fascicles.

Epimysium

A dense irregular connective tissue sheath that surrounds the entire muscle.

Tendon vs. Aponeurosis

A tendon is a cordlike structure attaching muscle to bone or another muscle, whereas an aponeurosis is a sheetlike structure with similar functions.

Neuromuscular junction

The synapse formed between the axon terminal of a motor neuron and a muscle fiber.

Motor unit

A functional structure consisting of a motor neuron and the muscle fibers it stimulates.

Synaptic cleft

The small fluid-filled gap that separates the axon terminal of a motor neuron and the sarcolemma of a muscle fiber.

Acetylcholine (ACh)

A neurotransmitter released at the neuromuscular junction that triggers muscle contraction.

Z disc

A structure that defines the boundaries of a sarcomere and anchors thin filaments.

M line

The line in the middle of the sarcomere that anchors thick filaments.

A band vs. I band

A band is the darker area of the sarcomere that contains thick filaments, while I band is the lighter area that contains only thin filaments.