Chapter 8: Muscular System

Comprehensive vocabulary flashcards covering the structural hierarchy, cellular anatomy, sarcomere architecture, neuromuscular junction signaling, cross-bridge cycling, energy metabolism, and mechanics of the muscular system based on Chapter 8.

Fascia

Layers of dense connective tissue that surround and separate each muscle, giving rise to tendons that fuse to the periosteum of bones.

Tendon

A cord-like band of dense connective tissue arising from fascia that attaches a muscle to the periosteum of a bone.

Epimysium

The layer of connective tissue that closely surrounds each whole skeletal muscle.

Perimysium

The connective tissue layer that surrounds individual bundles of muscle fibers, known as fascicles, within a muscle.

Fascicle

A bundle of skeletal muscle cells (muscle fibers) wrapped by perimysium.

Endomysium

The delicate layer of connective tissue that surrounds each individual muscle cell (fiber).

Aponeurosis

A broad, fibrous sheet of connective tissue that attaches a muscle to the coverings of adjacent muscles.

Sarcolemma

The specialized cell membrane of a skeletal muscle fiber.

Sarcoplasm

The cytoplasm of a muscle cell, containing many nuclei, mitochondria, and myofibrils.

Sarcoplasmic Reticulum

A specialized network of membranous channels (endoplasmic reticulum) beneath the sarcolemma that stores and releases calcium ions.

Transverse Tubules (T Tubules)

Membranous channels extending inward from the sarcolemma deep into the muscle fiber that carry electrical impulses to the myofilaments.

Myofibrils

Cylindrical bundles of protein myofilaments (actin and myosin) located within a muscle fiber.

Actin

The thin protein myofilament composed of globular subunits containing binding sites for myosin cross-bridges.

Myosin

The thick protein myofilament consisting of two twisted protein strands with outward-projecting globular cross-bridges.

Sarcomere

The structural and functional unit of a muscle fiber, extending from one Z line to the next consecutive Z line.

I Band

The light band of a sarcomere composed exclusively of thin actin filaments anchored to Z lines.

A Band

The dark region of a sarcomere consisting of thick myosin filaments overlapping with thin actin filaments.

H Zone

The central, lighter region of an A band composed entirely of thick myosin filaments without overlapping actin.

Z Line

The structural boundary defining the borders of each sarcomere where actin filaments are anchored.

M Line

The central protein line in the middle of a sarcomere that anchors the thick myosin filaments.

Neuromuscular Junction

The functional connection and site where a motor neuron and a skeletal muscle fiber meet.

Motor End Plate

A specialized, deeply folded region of sarcolemma at the neuromuscular junction containing abundant nuclei, mitochondria, and neurotransmitter receptors.

Acetylcholine (ACh)

The neurotransmitter released from synaptic vesicles at the axon terminal that stimulates skeletal muscle contraction.

Acetylcholinesterase

The enzyme located in the synaptic cleft that rapidly decomposes acetylcholine, preventing continuous muscle fiber stimulation.

Sliding Filament Theory

The mechanism of muscle contraction stating that actin and myosin filaments slide past each other, shortening the sarcomeres without altering filament length.

Tropomyosin

A rod-shaped regulatory protein that lies in the grooves of the actin filament, blocking myosin binding sites in a resting muscle.

Troponin

A regulatory protein complex attached to tropomyosin that binds calcium ions, causing tropomyosin to shift and expose myosin binding sites.

Cross-Bridge

The globular head of a myosin molecule that binds to an exposed site on actin to perform a power stroke pulling the thin filament.

Motor Unit

A single motor neuron together with all of the skeletal muscle fibers that it innervates and controls.

Creatine Phosphate

A high-energy biochemical molecule that stores excess energy in muscle tissue and transfers a phosphate group to $ADP$ to regenerate $ATP$.

Myoglobin

A reddish-brown, iron-containing pigment synthesized in muscle cells that temporarily stores oxygen.

Hemoglobin

The oxygen-carrying protein pigment found in red blood cells that transports oxygen to skeletal muscles.

Lactic Acid

An organic compound produced during anaerobic respiration when oxygen is deficient, which diffuses into the blood, lowers pH, and travels to the liver.

Oxygen Debt

The amount of oxygen required by liver cells to convert accumulated lactic acid to glucose plus the amount required by muscle cells to restore $ATP$ and creatine phosphate levels.

Muscle Fatigue

A condition in which a muscle loses its ability to contract during strenuous exercise, typically caused by lactic acid accumulation and a deficiency of $ATP$.

Muscle Cramp

A painful, sustained involuntary muscle contraction that occurs due to a localized lack of $ATP$ needed to return calcium ions to the sarcoplasmic reticulum.

Threshold Stimulus

The minimal strength of electrical or neural stimulation necessary to elicit a contraction response in a muscle fiber.

All-or-None Response

The physiological phenomenon wherein a muscle fiber responds completely to a threshold stimulus or does not contract at all.

Myogram

A recorded tracing of the mechanical contraction response of an electrically stimulated muscle over time.

Latent Period

The brief time interval on a myogram between the application of a stimulus and the onset of muscle contraction.

Summation

The process by which rapid, successive stimuli produce increasingly strong contractions because calcium ions do not have time to fully return to the sarcoplasmic reticulum.

Recruitment

An increase in the number of activated motor units within a muscle as the intensity of stimulation increases.

Muscle Tone

A continuous state of partial, sustained contraction of motor units within a muscle that maintains posture and firmness.

Prime Mover

The muscle in a functional group that is primarily responsible for producing a specific movement.

Synergist

A muscle that assists the prime mover by contributing to the same movement or stabilizing nearby joints.

Antagonist

A muscle that opposes the action of a prime mover and can cause movement in the opposite direction.