Human Anatomy — Muscular System

Myosin

A thick filament protein that interacts with actin for muscle contraction

Neuromuscular junction

The synapse between a motor neuron and a skeletal muscle fiber

Acetylcholine

Neurotransmitter released at the neuromuscular junction to stimulate muscle contraction

Sliding filament theory

The process by which actin and myosin filaments slide over each other during muscle contraction

Tendons

Connective tissues that attach muscles to bones

Ligaments

Connective tissues that connect bones to other bones

Motor unit

A single motor neuron and all the muscle fibers it innervates

Muscle hypertrophy

An increase in muscle size due to an increase in the size of individual muscle fibers

Muscle atrophy

A decrease in muscle mass due to disuse or denervation

Isometric contraction

Muscle contraction without a change in muscle length

Isotonic contraction

Muscle contraction with a change in muscle length

Fast-twitch fibers

Muscle fibers that contract quickly and generate high force but fatigue rapidly

Slow-twitch fibers

Muscle fibers that contract slowly and are resistant to fatigue

Glycolysis

A metabolic pathway that converts glucose into pyruvate, providing energy for muscle contractions

Creatine phosphate

A molecule that can quickly donate a phosphate to ADP to regenerate ATP in muscle cells

What is the role of calcium in muscle contraction?

Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from actin's myosin-binding sites, allowing contraction.

Troponin

A protein complex involved in muscle contraction that binds calcium ions

Tropomyosin

A protein that blocks myosin-binding sites on actin molecules in resting muscle

Rigor mortis

A postmortem condition where muscles become stiff due to the lack of ATP required to release myosin from actin

ATP's role in muscle contraction

ATP binds to myosin, allowing it to detach from actin and re-cock for another power stroke

Endomysium

Connective tissue surrounding individual muscle fibers

Perimysium

Connective tissue surrounding a bundle of muscle fibers (fascicle)

Epimysium

Connective tissue surrounding an entire muscle

What is muscle fatigue?

The decline in ability of a muscle to generate force, often due to prolonged activity, lack of energy, or accumulation of metabolic byproducts.

Myoglobin

An oxygen-binding protein in muscle cells that provides a reserve of oxygen for aerobic ATP production

What is the function of the sarcoplasmic reticulum?

The sarcoplasmic reticulum stores calcium ions and releases them upon stimulation to initiate muscle contraction.

Muscle spindle

A sensory receptor located in muscles that senses changes in muscle length

Golgi tendon organ

A sensory receptor located at the junction of a muscle and its tendon, sensitive to changes in muscle tension

Fascicle

A bundle of skeletal muscle fibers surrounded by perimysium

What is the all-or-none principle in muscle contraction?

A muscle fiber will contract to its full potential when stimulated; there is no partial contraction.

Origin of a muscle

The fixed attachment point of a muscle, typically proximal

Insertion of a muscle

The movable attachment point of a muscle, typically distal

What is the role of ATPase in muscle contraction?

ATPase is an enzyme on the myosin head that hydrolyzes ATP, providing energy for the power stroke during contraction.