Muscular System - Lecture Notes

Vocabulary flashcards covering skeletal, smooth, and cardiac muscles, key structures, proteins, energy systems, neuromuscular junction, and related disorders.

Skeletal muscle

Voluntary, striated muscle with multinucleated fibers organized into sarcomeres for body movement.

Fascicle

A bundle of muscle fibers surrounded by perimysium.

Endomysium

Connective tissue that surrounds individual muscle fibers.

Perimysium

Connective tissue that wraps a group of fibers forming a fascicle.

Epimysium

Connective tissue surrounding the entire muscle; forms tendons at the ends.

Myofibril

Contractile rod inside a muscle fiber composed of repeating sarcomeres.

Myofilaments

Thick (myosin) and thin (actin) filaments that slide past each other during contraction.

Actin

Thin filament; interacts with myosin during contraction; anchored to Z-lines.

Myosin

Thick filament with heads that form cross-bridges with actin during contraction.

Sarcomere

Functional contractile unit of a myofibril, from one Z-line to the next.

Z-line (Z-disc)

Boundary that defines the ends of a sarcomere and anchors actin.

I-band

Region of the sarcomere containing only actin filaments.

A-band

Region containing the full length of the myosin filament, with overlap of actin.

H-band

Central zone within the A-band where only myosin is present.

Troponin

Calcium-binding complex on actin that regulates access to myosin-binding sites via tropomyosin.

Tropomyosin

Regulatory protein that blocks actin-myosin binding at rest and moves off with Ca2+-Troponin.

Calcium (Ca2+)

Ion that triggers contraction by moving troponin-tropomyosin to expose binding sites.

Cross-bridge

Interaction between myosin heads and actin filaments during contraction.

ATP

Adenosine triphosphate; energy source for contraction and cross-bridge cycling.

Phosphocreatine

High-energy phosphate reserve that rapidly regenerates ATP in muscle.

Glycogen

Stored glucose in muscle; digested to provide glucose for glycolysis.

Myoglobin

Oxygen-binding protein in muscle; stores oxygen and aids endurance, higher in red fibers.

Slow-twitch (red) fibers

High myoglobin and mitochondria; fatigue-resistant, slower contractions.

Fast-twitch (white) fibers

Lower myoglobin; rapid, powerful contractions; fatigue quickly.

Neuromuscular junction

Synapse between a motor neuron and a muscle fiber; acetylcholine triggers depolarization.

Acetylcholine

Neurotransmitter released at the neuromuscular junction to stimulate contraction.

Botulinum toxin

Blocks acetylcholine release, causing muscle paralysis.

Myasthenia gravis

Autoimmune disease against acetylcholine receptors leading to muscle weakness.

Sarcolemma

Plasma membrane of a muscle fiber.

Triad

Structure of T-tubule and two terminal cisternae of the sarcoplasmic reticulum that facilitates Ca2+ release.

T-tubules

Invaginations of the sarcolemma that propagate action potentials into the muscle fiber.

Sarcoplasmic reticulum

Organelle storing Ca2+ and releasing it during contraction.

Intercalated discs

junctions that connect cardiac muscle cells for synchronized contraction.

Sinoatrial node

Natural pacemaker of the heart that initiates the heartbeat.