Chapter 1: Structure and Function of Exercising Muscle - Vocabulary

Vocabulary flashcards covering key terms from Chapter 1 notes on muscle structure, contraction, recruitment, fiber types, and excitation–contraction coupling.

Smooth muscle

Involuntary muscle tissue found in the walls of hollow organs and vessels.

Cardiac muscle

Involuntary muscle tissue of the heart that contracts to pump blood.

Skeletal muscle

Voluntary muscle attached to the skeleton responsible for movement.

Epimysium

Outer connective tissue sheath surrounding the entire muscle; transmits force.

Perimysium

Connective tissue surrounding a fascicle (bundle) of muscle fibers.

Endomysium

Connective tissue surrounding each individual muscle fiber.

Fasciculus (fascicle)

Bundle of muscle fibers within a muscle.

Sarcolemma

Plasma membrane of a muscle fiber.

Sarcoplasm

Cytoplasm of a muscle fiber.

Myofibril

Long contractile elements inside a muscle fiber containing sarcomeres.

A band

Region of the sarcomere containing thick filaments; length remains constant during contraction.

I band

Region of the sarcomere containing thin filaments; shortens during contraction.

Z line

Boundary of a sarcomere; anchor point for actin filaments.

Sarcomere

Functional unit of a myofibril, extending from Z line to Z line.

Myofilament

Contractile proteins within a sarcomere (actin and myosin).

Actin

Thin filament with binding sites for myosin.

Myosin

Thick filament that forms cross-bridges with actin during contraction.

Troponin complex

Calcium-binding proteins on actin that move tropomyosin to expose binding sites.

Tropomyosin

Proteins that block actin active sites at rest; moved by troponin.

Cross-bridge

Myosin head binding to actin, generating force via the power stroke.

Motor unit

A motor neuron and all the muscle fibers it innervates.

Alpha-motor neuron

Motor neuron that innervates skeletal muscle fibers.

Neuromuscular junction

Synapse between an alpha-motor neuron and a muscle fiber.

Acetylcholine (ACh)

Neurotransmitter released at the NMJ to trigger depolarization.

Acetylcholinesterase

Enzyme that degrades acetylcholine in the synaptic cleft.

Ligand-gated ion channel

Ion channel opened by binding of a chemical messenger (neurotransmitter).

Voltage-gated ion channel

Ion channel opened by changes in membrane potential.

Resting membrane potential

Typical inside-negative voltage of -90 mV in skeletal muscle.

Depolarization

Decrease in membrane polarization; inside becomes more positive.

DHP receptor

Voltage-sensing receptor in T-tubules that triggers Ca2+ release from SR.

Ryanodine receptor

SR membrane channel that releases Ca2+ into the cytosol.

Transverse tubule (T-tubule)

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

Sarcoplasmic reticulum

Organelle that stores and releases Ca2+ during contraction.

Ca2+ (calcium)

Ion that binds troponin to initiate cross-bridge cycling.

Troponin

Calcium-binding protein on actin that moves tropomyosin off the binding sites.

ATP

Adenosine triphosphate; energy source for cross-bridge cycling.

ATPase

Enzyme that hydrolyzes ATP to energize the myosin head.

Power stroke

Myosin pivot that slides actin past myosin, shortening the sarcomere.

Sliding Filament Theory

Contraction mechanism where actin and myosin slide past each other after Ca2+ release.

Excitation-contraction coupling

Process linking neural stimulation to muscle contraction (NMJ → AP → Ca2+ release → cross-bridge cycling).

Type I fiber

Slow-twitch fiber with high oxidative capacity; fatigue resistant.

Type IIa fiber

Fast-twitch, fast oxidative/glycolytic fiber; intermediate properties.

Type IIx fiber

Fast-twitch glycolytic fiber; high speed, lower oxidative capacity.

Fibers per motor neuron

Number of muscle fibers innervated by a single motor neuron; varies by fiber type (fewer in Type I, more in Type II).

Motor neuron conduction velocity

Speed of impulse along the motor neuron; faster in Type II fibers.

Size principle

Smallest motor units recruited first; progressively larger units recruited as force increases.

Recruitment order

Sequential activation of motor units from smallest to largest with increasing demand.

Isometric contraction

Static contraction where joint angle and muscle length remain unchanged.

Concentric contraction

Dynamic contraction where the muscle shortens while producing force.

Eccentric contraction

Dynamic contraction where the muscle lengthens while producing force.

Length-tension relationship

There is an optimal sarcomere length for maximal force; too short/too stretched reduces force.

Force-velocity relationship

Maximal force decreases as shortening velocity increases during concentric actions.