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Chapter 13 Muscles - Anatomy & Physiology

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Terms in this set (35)

  • What is the sarcoplasm?
    The sarcoplasm is the cytoplasm of a muscle fiber, containing organelles and myofibrils.
  • What is the sarcolemma?
    The sarcolemma is the plasma membrane of a muscle fiber that surrounds the sarcoplasm.
  • What are Transverse Tubules (T-tubules)?
    T-tubules are invaginations of the sarcolemma that penetrate into the muscle fiber and contain voltage-gated ion channels.
  • Order muscle fibers, myofibrils, and myofilaments from largest to smallest.
    Muscle fibers > Myofibrils > Myofilaments.
  • What is the sarcoplasmic reticulum and its function?
    The sarcoplasmic reticulum is a specialized smooth ER that stores and releases calcium ions for muscle contraction.
  • What are Terminal Cisternae?
    Terminal cisternae are enlarged areas of the sarcoplasmic reticulum that flank T-tubules and release calcium during contraction.
  • What is a Triad in muscle fibers?
    A triad consists of a T-tubule flanked by two terminal cisternae of the sarcoplasmic reticulum.
  • What types of pumps are in the sarcoplasmic reticulum?
    The sarcoplasmic reticulum contains calcium pumps that actively transport calcium ions back into the SR.
  • What are myofilaments?
    Myofilaments are the contractile proteins within myofibrils, including thick filaments (myosin) and thin filaments (actin).
  • Which proteins are found on thick and thin filaments?
    Thick filaments contain myosin. Thin filaments contain actin, tropomyosin, and troponin.
  • Which myofilament proteins are regulatory?
    Tropomyosin and troponin are regulatory proteins on thin filaments controlling contraction.
  • What is a sarcomere?
    A sarcomere is the functional contractile unit of a muscle fiber, defined by Z-disks at each end.
  • What are Z-disks?
    Z-disks are protein structures that define the boundaries of a sarcomere and anchor thin filaments.
  • Define A-bands and I-bands in a sarcomere.
    The A-band contains thick filaments and overlapping thin filaments; the I-band contains only thin filaments.
  • Which band shortens during muscle contraction?
    The I-band shortens during contraction as thin filaments slide over thick filaments.
  • Where is the H-zone located?
    The H-zone is the central region of the A-band with only thick filaments and no overlap.
  • What is the M-line?
    The M-line is the center of the sarcomere where thick filaments are anchored.
  • What are titin and nebulin?
    Titin stabilizes thick filaments and provides elasticity; nebulin helps align thin filaments.
  • What are the three parts of the neuromuscular junction?
    The synaptic knob, motor end plate, and synaptic cleft.
  • What is the synaptic knob and its contents?
    The synaptic knob is the axon terminal containing synaptic vesicles filled with acetylcholine (ACh).
  • What is the function of calcium pumps at the synaptic knob?
    Calcium pumps maintain low intracellular calcium until an action potential triggers calcium entry.
  • What happens when voltage-gated calcium channels open at the synaptic knob?
    Calcium enters the synaptic knob, triggering ACh release into the synaptic cleft.
  • Where is the motor end plate and its function?
    The motor end plate is the specialized region of the muscle fiber membrane with ACh receptors.
  • What is the synaptic cleft?
    The synaptic cleft is the space separating the synaptic knob and motor end plate.
  • What establishes the resting membrane potential (RMP) of muscle cells?
    The RMP (~ -90 mV) is established by ion gradients and selective permeability, mainly potassium leak channels.
  • What triggers calcium entry at the synaptic knob during muscle contraction?
    An action potential arriving at the synaptic knob opens voltage-gated calcium channels.
  • What is an end plate potential (EPP)?
    An EPP is a local depolarization caused by ACh binding, allowing sodium influx at the motor end plate.
  • Describe depolarization and repolarization in muscle action potentials.
    Depolarization is sodium influx raising membrane potential; repolarization is potassium efflux restoring RMP.
  • What is the refractory period?
    The refractory period is the time after an action potential when the muscle fiber cannot be re-excited.
  • Where does the action potential travel to stimulate calcium release?
    It travels along the sarcolemma and down T-tubules to the sarcoplasmic reticulum.
  • What does calcium bind to in the sarcoplasm to initiate contraction?
    Calcium binds to troponin on thin filaments, causing tropomyosin to move and expose myosin-binding sites.
  • What are the four steps of cross-bridge cycling?
    1. Cross-bridge formation, 2. Power stroke, 3. Cross-bridge detachment, 4. Reactivation of myosin head.
  • What happens to the H-zone and I-band during cross-bridge cycling?
    Both the H-zone and I-band shorten as thin filaments slide over thick filaments.
  • What causes central and peripheral muscle fatigue?
    Central fatigue is due to CNS factors; peripheral fatigue results from changes within the muscle like ion imbalance.
  • Basic differences between smooth and skeletal muscle?
    Smooth muscle is involuntary, non-striated, and has single nuclei; skeletal muscle is voluntary, striated, and multinucleated.