Human Anatomy – Skeletal Muscle Tissue & Organization (Chapter 9)

A comprehensive set of vocabulary flashcards covering key terms and concepts from Chapter 9 on skeletal muscle tissue and organization.

Muscle Fiber

Elongated skeletal muscle cell capable of contraction; also called a muscle cell.

Skeletal Muscle

Voluntary muscle that pulls on bones to produce body movement.

Cardiac Muscle

Rhythmic, involuntary muscle tissue that forms the heart wall.

Smooth Muscle

Involuntary muscle that pushes fluids and solids through internal passageways (e.g., digestive tract).

Excitability

Property of muscle tissue that allows it to respond to stimuli.

Contractility

Ability of a muscle to shorten and generate tension.

Extensibility

Capacity of muscle to contract over a range of resting lengths.

Elasticity

Ability of muscle to rebound to its original length after stretching.

Epimysium

Dense connective tissue sheath that surrounds an entire muscle.

Perimysium

Connective tissue that divides a muscle into fascicles (parallel compartments).

Endomysium

Connective tissue layer that surrounds individual muscle fibers.

Tendon

Cord-like structure formed by merged muscle sheaths that connects muscle to bone.

Aponeurosis

Broad, flat sheet of connective tissue that connects muscle to muscle.

Neuromuscular Junction (NMJ)

Site where a motor neuron communicates chemically with a skeletal muscle fiber.

Sarcolemma

Plasma membrane that encloses a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle fiber containing organelles and myofibrils.

Myoblast

Embryonic cell that fuses with others to form a skeletal muscle fiber.

Myosatellite Cell

Stem-like cell derived from myoblasts that aids in muscle repair and regeneration.

Transverse (T) Tubule

Invagination of the sarcolemma that conducts electrical impulses into the fiber’s interior.

Myofibril

Cylindrical structure within a muscle fiber composed of repeating sarcomeres.

Myofilament

Protein filament (actin or myosin) that composes myofibrils and allows contraction.

Actin

Thin protein filament within sarcomeres; anchors to Z lines.

Myosin

Thick protein filament with club-shaped heads that form cross-bridges during contraction.

Sarcoplasmic Reticulum (SR)

Smooth ER of a muscle fiber that stores and releases Ca²⁺ for contraction.

Terminal Cisternae

Expanded chambers of the SR adjoining T tubules; part of the triad.

Triad

Structure formed by a T tubule flanked by two terminal cisternae.

Sarcomere

Smallest functional unit of a myofibril; contains organized actin and myosin.

Z Line (Z Disc)

Boundary of a sarcomere to which thin filaments attach.

I Band

Light band of a sarcomere containing only actin filaments.

A Band

Dark band containing overlapping actin and myosin filaments.

Zone of Overlap

Region within the A band where actin and myosin overlap, producing striations.

H Band

Central zone of the A band that contains only myosin filaments.

M Line

Center of the H band; proteins stabilize thick filaments.

Sliding Filament Theory

Model stating that muscle contraction occurs as thin filaments slide past thick filaments, shortening sarcomeres.

Motor Unit

Single motor neuron and all the muscle fibers it innervates.

Recruitment

Increase in force of contraction by activating additional motor units.

All-or-None Principle

A muscle fiber contracts completely or not at all when stimulated above threshold.

Muscle Tone

Baseline tension in a relaxed muscle that stabilizes bones and joints.

Muscle Hypertrophy

Increase in muscle size due to more mitochondria, glycogen, and myofibrils from exercise.

Muscle Atrophy

Decrease in muscle mass and strength from disuse or aging.

Fast Fibers (White Fibers)

Large-diameter fibers that contract quickly, fatigue rapidly, and rely on anaerobic metabolism.

Slow Fibers (Red Fibers)

Smaller fibers rich in myoglobin and mitochondria; contract slowly and resist fatigue via aerobic metabolism.

Intermediate Fibers (Pink Fibers)

Muscle fibers with traits between fast and slow types; moderate speed and fatigue resistance.

Myoglobin

Oxygen-binding pigment in muscle that gives slow fibers their red color.

Parallel Muscle

Muscle with fascicles parallel to its long axis; e.g., biceps brachii.

Convergent Muscle

Muscle whose fibers spread out over a broad area and converge on a common tendon; e.g., pectoralis major.

Pennate Muscle

Muscle with fascicles at an oblique angle to the tendon, enhancing force.

Unipennate

Pennate muscle with fibers on one side of the tendon; e.g., extensor digitorum.

Bipennate

Pennate muscle with fibers on both sides of a central tendon; e.g., rectus femoris.

Multipennate

Pennate muscle with multiple tendon branches within; e.g., deltoid.

Circular Muscle (Sphincter)

Muscle with concentric fibers that close openings; e.g., orbicularis oris.

Origin (Muscle)

Fixed attachment site of a muscle that remains stationary during contraction.

Insertion (Muscle)

Movable attachment point of a muscle that is pulled toward the origin.

Prime Mover (Agonist)

Muscle chiefly responsible for producing a specific movement.

Antagonist

Muscle whose action opposes that of an agonist.

Synergist

Muscle that assists the prime mover in performing its action.

Fixator

Muscle that stabilizes the origin of the prime mover by contracting simultaneously with agonist and antagonist.

Tropomyosin

Regulatory protein that covers active sites on actin in resting muscle.

Troponin

Calcium-binding protein that moves tropomyosin, exposing actin active sites for contraction.

Titin

Elastic protein that connects thick filaments to Z lines, helping muscle recoil after stretching.