🍖 | Chapter 9 : Skeletal Muscle Tissue

Vocabulary flashcards covering key terms and structures involved in skeletal muscle anatomy, physiology, and contraction mechanisms.

Skeletal Muscle Tissue

Voluntary muscle that moves the body by pulling on bones.

Cardiac Muscle Tissue

Involuntary muscle found only in the heart that pumps blood.

Smooth Muscle Tissue

Involuntary muscle in walls of hollow organs and vessels; moves substances and regulates diameter.

Epimysium

Dense irregular connective tissue that surrounds the entire muscle organ.

Perimysium

Connective tissue sheath that surrounds each fascicle within a muscle.

Endomysium

Thin areolar connective tissue surrounding an individual muscle fiber and housing capillaries and nerves.

Muscle Fascicle

A bundle of skeletal muscle fibers wrapped by perimysium.

Muscle Fiber

A single skeletal muscle cell; elongated and multinucleated.

Myofibril

Cylindrical bundle of myofilaments inside a muscle fiber; responsible for contraction.

Myofilaments

Protein filaments (thin and thick) that slide to produce muscle contraction.

Sarcolemma

Plasma membrane of a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle fiber, containing mitochondria, myofibrils, and glycogen.

Sarcomere

Basic contractile unit of a myofibril, spanning Z line to Z line.

Z Line (Z Disc)

Boundary between sarcomeres; anchors thin filaments via actinin proteins.

I Band

Light band containing only thin filaments; shortens during contraction.

A Band

Dark band containing entire length of thick filaments plus overlap with thin filaments; width stays constant.

H Zone

Central region of A band with only thick filaments in resting muscle.

M Line

Center of H zone; proteins that stabilize and align thick filaments.

T (Transverse) Tubules

Invaginations of sarcolemma that transmit action potentials deep into the fiber.

Sarcoplasmic Reticulum (SR)

Smooth ER–like network that stores and releases Ca²⁺ for contraction.

Terminal Cisternae

Enlarged SR chambers adjacent to T tubules; part of the triad.

Triad

Structure composed of one T tubule flanked by two terminal cisternae; coordinates Ca²⁺ release.

Thin Filament

Actin-based filament containing F-actin, tropomyosin, and troponin.

F-Actin

Twisted filament of G-actin subunits forming the backbone of thin filaments.

G-Actin

Globular actin molecule with an active site for myosin binding.

Troponin

Three-subunit protein that binds Ca²⁺, G-actin, and tropomyosin to regulate contraction.

Tropomyosin

Double-stranded protein that covers G-actin active sites at rest, preventing myosin binding.

Thick Filament

Bundle of ~300 myosin molecules with heads that form cross-bridges.

Myosin

Motor protein with tail and two heads that bind actin and ATP to generate force.

Sliding Filament Theory

Model stating thin filaments slide past thick filaments, shortening sarcomeres and muscle fibers.

Neuromuscular Junction (NMJ)

Synapse between a motor neuron and a skeletal muscle fiber.

Axon Terminal

End of a motor neuron containing synaptic vesicles filled with acetylcholine.

Synaptic Cleft

Space between axon terminal and motor end plate where ACh diffuses.

Motor End Plate

Specialized region of sarcolemma containing ACh receptors.

Acetylcholine (ACh)

Neurotransmitter that triggers action potentials in muscle fibers.

Acetylcholinesterase (AChE)

Enzyme in synaptic cleft that breaks down ACh, ending stimulation.

Cross-Bridge

Connection between a myosin head and an actin active site during contraction.

Power Stroke

Pivoting movement of the myosin head that pulls thin filaments toward the M line.

Muscle Hypertrophy

Increase in muscle fiber size from repeated stimulation and growth of myofibrils.

Muscle Atrophy

Decrease in muscle fiber size and strength due to lack of stimulation.

Fibrosis

Increase in fibrous connective tissue, reducing muscle elasticity, common with aging.

ATP (Adenosine Triphosphate)

Primary energy molecule required for cross-bridge cycling and muscle contraction.