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13.12: Glossary- Muscle Tissue

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    ATPase: enzyme that hydrolyzes ATP to ADP

    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

    angiogenesis: formation of blood capillary networks

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

    atrophy: loss of structural proteins from muscle fibers

    autorhythmicity: heart’s ability to control its own contractions

    calmodulin: regulatory protein that facilitates contraction in smooth muscles

    cardiac muscle: striated muscle found in the heart; joined to one another at intercalated discs and under the regulation of pacemaker cells, which contract as one unit to pump blood through the circulatory system. Cardiac muscle is under involuntary control.

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

    contractility: ability to shorten (contract) forcibly

    contraction phase: twitch contraction phase when tension increases

    creatine phosphate: phosphagen used to store energy from ATP and transfer it to muscle

    dense body: sarcoplasmic structure that attaches to the sarcolemma and shortens the muscle as thin filaments slide past thick filaments

    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

    desmosome: cell structure that anchors the ends of cardiac muscle fibers to allow contraction to occur

    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

    graded muscle response: modification of contraction strength

    hyperplasia: process in which one cell splits to produce new cells

    hypertonia: abnormally high muscle tone

    hypertrophy: addition of structural proteins to muscle fibers

    hypotonia: abnormally low muscle tone caused by the absence of low-level contractions

    intercalated disc: part of the sarcolemma that connects cardiac tissue, and contains gap junctions and desmosomes

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

    isotonic contraction: muscle contraction that involves changes in muscle length

    lactic acid: product of anaerobic glycolysis

    latch-bridges: subset of a cross-bridge in which actin and myosin remain locked together

    latent period: the time when a twitch does not produce contraction

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

    motor unit: motor neuron and the group of muscle fibers it innervates

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

    muscle tone: low levels of muscle contraction that occur when a muscle is not producing movement

    myoblast: muscle-forming stem cell

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

    myogram: instrument used to measure twitch tension

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

    myotube: fusion of many myoblast cells

    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

    oxygen debt: amount of oxygen needed to compensate for ATP produced without oxygen during muscle contraction

    pacesetter cell: cell that triggers action potentials in smooth muscle

    pericyte: stem cell that regenerates smooth muscle 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)

    pyruvic acid: product of glycolysis that can be used in aerobic respiration or converted to lactic acid

    recruitment: increase in the number of motor units involved in contraction

    relaxation phase: period after twitch contraction when tension decreases

    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

    sarcopenia: age-related muscle atrophy

    sarcoplasmic reticulum (SR): specialized smooth endoplasmic reticulum, which stores, releases, and retrieves Ca++

    sarcoplasm: cytoplasm of a muscle cell

    satellite cell: stem cell that helps to repair muscle cells

    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

    somites: blocks of paraxial mesoderm cells

    stress-relaxation response: relaxation of smooth muscle tissue after being stretched

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

    T-tubule: projection of the sarcolemma into the interior of the cell

    tetanus: a continuous fused contraction

    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

    treppe: stepwise increase in contraction tension

    triad: the grouping of one T-tubule and two terminal cisternae

    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

    twitch: single contraction produced by one action potential

    varicosity: enlargement of neurons that release neurotransmitters into synaptic clefts

    visceral muscle: smooth muscle found in the walls of visceral organs

    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

    wave summation: addition of successive neural stimuli to produce greater contraction

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