Chapter 3 – Key Terms

acetylcholine (ACh) neurotransmitter that binds at a motor end-plate to trigger depolarization

actin protein that makes up most of the thin myofilaments in a sarcomere muscle fiber

action potential change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers

aerobic respiration production of ATP in the presence of oxygen

aponeurosis broad, tendon-like sheet of connective tissue that attaches a skeletal muscle to another skeletal muscle or to a bone

concentric contraction muscle contraction that shortens the muscle to move a load

contractility ability to shorten (contract) forcibly

depolarize to reduce the voltage difference between the inside and outside of a cell’s plasma membrane (the sarcolemma for a muscle fiber), making the inside less negative than at rest

eccentric contraction muscle contraction that lengthens the muscle as the tension is diminished

elasticity ability to stretch and rebound

endomysium loose, and well-hydrated connective tissue covering each muscle fiber in a skeletal muscle

epimysium outer layer of connective tissue around a skeletal muscle

excitability ability to undergo neural stimulation

excitation-contraction coupling sequence of events from motor neuron signaling to a skeletal muscle fiber to contraction of the fiber’s sarcomeres

extensibility ability to lengthen (extend)

fascicle bundle of muscle fibers within a skeletal muscle

fast glycolytic (FG) muscle fiber that primarily uses anaerobic glycolysis

fast oxidative (FO) intermediate muscle fiber that is between slow oxidative and fast glycolytic fibers

fibrosis replacement of muscle fibers by scar tissue

glycolysis anaerobic breakdown of glucose to ATP

isometric contraction muscle contraction that occurs with no change in muscle length

isotonic contraction muscle contraction that involves changes in muscle length

motor end-plate sarcolemma of muscle fiber at the neuromuscular junction, with receptors for the neurotransmitter acetylcholine

muscle tension force generated by the contraction of the muscle; tension generated during isotonic contractions and isometric contractions

myofibril long, cylindrical organelle that runs parallel within the muscle fiber and contains the sarcomeres

myosin protein that makes up most of the thick cylindrical myofilament within a sarcomere muscle fiber

neuromuscular junction (NMJ) synapse between the axon terminal of a motor neuron and the section of the membrane of a muscle fiber with receptors for the acetylcholine released by the terminal

neurotransmitter signaling chemical released by nerve terminals that bind to and activate receptors on target cells

perimysium connective tissue that bundles skeletal muscle fibers into fascicles within a skeletal muscle

power stroke action of myosin pulling actin inward (toward the M line)

sarcolemma plasma membrane of a skeletal muscle fiber

sarcomere longitudinally, repeating functional unit of skeletal muscle, with all of the contractile and associated proteins involved in contraction

sarcoplasm cytoplasm of a muscle cell

skeletal muscle striated, multinucleated muscle that requires signaling from the nervous system to trigger contraction; most skeletal muscles are referred to as voluntary muscles that move bones and produce movement

slow oxidative (SO) muscle fiber that primarily uses aerobic respiration

smooth muscle nonstriated, mononucleated muscle in the skin that is associated with hair follicles; assists in moving materials in the walls of internal organs, blood vessels, and internal passageways

synaptic cleft space between a nerve (axon) terminal and a motor end-plate

thick filament the thick myosin strands and their multiple heads projecting from the center of the sarcomere toward, but not all to way to, the Z-discs

thin filament thin strands of actin and its troponin-tropomyosin complex projecting from the Z-discs toward the center of the sarcomere

tropomyosin regulatory protein that covers myosin-binding sites to prevent actin from binding to myosin

troponin regulatory protein that binds to actin, tropomyosin, and calcium

voltage-gated sodium channels membrane proteins that open sodium channels in response to a sufficient voltage change, and initiate and transmit the action potential as Na⁺ enters through the channel