Muscular System

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Acetylcholine - Chemical messenger released from the end of a motor neuron

Actin - Protein of which the thin myofilaments are composed

Aerobic respiration - Process that breaks down fatty acids for energy when oxygen is

present

Anaerobic respiration - Process that breaks down glucose for energy when oxygen is not

plentiful

Antagonist - Muscles that oppose the action of a prime mover

Aponeurosis - Flat, broad tendon that attaches a muscle to another muscle or to bone

ATP - Adenosine triphosphate; used for energy in cells to perform various functions,

including muscle contraction

Atrophy - Decrease in the size of a muscle

Belly - The thick midsection of the muscle

Complete tetanus - Condition in which impulses arrive so fast the muscle cannot relax

between stimuli and twitches merge into one prolonged contraction

Creatine phosphate - Compound stored in muscle that is used for short bursts of high-

energy activity

Endomysium - Delicate connective tissue covering each muscle fiber

Epimysium - Connective tissue covering that surrounds muscles as a whole and binds all

muscle fibers together

Fascia - Connective tissue surrounding the muscle

Fascicles - Bundles of muscle fibers

Hypertrophy - Enlargement of a muscle

Incomplete tetanus - Condition of rapid muscle contraction with only partial relaxation

Insertion - The end of a muscle that attaches to the more mobile bone

Isometric contraction - Contraction in which the tension within a muscle increases while

its length remains the same

Isotonic contraction - Contraction in which the muscle changes length to move a load

Motor unit - A neuron and all the muscle fibers it stimulates

Muscle fiber - A skeletal muscle cell

Muscle tone - Continuous state of partial muscle contraction that allows for the

maintenance of posture

Myofibrils - Long protein bundles that fill the sarcoplasm of a muscle fiber

Myofilaments - Fine protein fibers that make up a myofibril

Myosin - Protein of which the thick myofilaments are composed

Neuromuscular junction - Connection between a motor neuron and a muscle fiber

Origin - The end of a muscle that attaches to the more stationary bone

Perimysium - Sheath of connective tissue encasing fascicles

Prime mover - The main muscle triggering a movement

Sarcomere - The unit of contraction of the myofibrils of a muscle

Sarcoplasm - The cytoplasm of a muscle fiber

Synaptic cleft - Narrow space between the end of a motor nerve and the muscle fiber

Synergists - Muscles that assist in the movement of a bone

Tendon - Strong, fibrous cord through which a muscle attaches to a bone

Transverse (T) tubules - Tubules that extend across the sarcoplasm and allow electrical

impulses to travel deep into the cell

Treppe - Phenomenon in which each successive twitch contracts more forcefully than the

previous one

Twitch - Single, brief contraction

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