ATPase

An enzyme that breaks down ATP to release energy

Synaptic cleft

The small gap between a neuron and a muscle fiber.

Synaptic vesicle

Small sacs in the neuron that store neurotransmitters like ACh.

Motor unit

One motor neuron and all the muscle fibers it controls.

Actin

Thin filament in muscle; works with myosin for contraction.

Myosin

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

Tropomyosin

A protein that blocks actin binding sites when muscle is relaxed.

Troponin

A protein that binds calcium to move tropomyosin and allow contraction.

Fascicles

Bundles of muscle fibers.

Fascia

Connective tissue surrounding muscles and other organs.

Epimysium

Connective tissue that surrounds the whole muscle.

Perimysium

Connective tissue around each fascicle.

Endomysium

Connective tissue around individual muscle fibers.

Tendon

Connects muscle to bone.

Sarcolemma

The cell membrane of a muscle fiber.

Sarcoplasm

Cytoplasm inside a muscle fiber

Sarcoplasmic reticulum (SR)

Stores calcium needed for muscle contraction.

T-tubules

Tubes that carry the action potential deep into the muscle fiber.

Aponeurosis

A flat sheet-like tendon.

Muscle fiber

A single muscle cell.

Myofilament

Actin and myosin filaments inside myofibrils.

Myofibril

Long protein rods inside muscle fibers made of sarcomeres.

Sarcomere

The functional unit of contraction in a muscle.

Neuromuscular junction (NMJ)

The connection site between a motor neuron and a muscle fiber

Motor end plate

The specialized region of the muscle fiber membrane at the NMJ.

Cross bridge

When myosin heads attach to actin during contraction.

Acetylcholine (ACh)

The neurotransmitter released to trigger muscle contraction.

Action potential

An electrical signal that travels along neurons and muscle fibers

Muscle fatigue

When a muscle loses its ability to contract effectively.

Isotonic contraction

Contraction where the muscle changes length (lifting weights).

Isometric contraction

Contraction with no change in muscle length.

Muscle tone

Constant slight contraction that keeps muscles firm.

Origin

The fixed attachment of a muscle.

Insertion

The attachment that moves when the muscle contracts.

Creatine Phosphate

A high-energy molecule that quickly regenerates ATP.

Elasticity

Ability of muscle to return to its original shape.

Contractility

Ability of muscle to shorten and generate force.

Excitability

Ability to receive and respond to stimuli.

Extensibility

Ability of muscle to stretch without damage.

Aerobic respiration

ATP production using oxygen