Muscle Physiology Quiz
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Questions and Answers

What is the primary function of acetylcholinesterase in the neuromuscular junction?

  • It transports choline back into the axon terminal.
  • It degrades acetylcholine in the synaptic cleft. (correct)
  • It stimulates the release of acetylcholine.
  • It initiates muscle contraction.

    • What is a consequence of the rapid destruction of acetylcholine?

  • It causes muscle fatigue.
  • It prevents repeated excitation of the muscle fiber. (correct)
  • It leads to increased neurotransmitter release.
  • It allows for sustained muscle contraction.

    • Which components make up a motor unit?

  • Motor neuron, its axon terminals, and the muscle fibers it innervates. (correct)
  • Muscle fibers and the neurotransmitters released.
  • Axon terminals and the acetylcholine molecules.
  • Single motor neuron and multiple axon terminals.

    • What happens to choline after acetylcholine is degraded by acetylcholinesterase?

    <p>It is reused in the formation of new acetylcholine molecules.</p> Signup and view all the answers

    How quickly is acetylcholine destroyed in the synaptic cleft?

    <p>Within 1 millisecond.</p> Signup and view all the answers

    What is the connective tissue sheath that covers each muscle fasciculus called?

    <p>Perimysium</p> Signup and view all the answers

    Which of the following structures is NOT embedded within the sarcoplasm of a muscle fiber?

    <p>Coronary arteries</p> Signup and view all the answers

    What is the average length of a muscle fiber?

    <p>3 cm</p> Signup and view all the answers

    What are the two types of bands present in the structure of a myofibril?

    <p>Light band and dark band</p> Signup and view all the answers

    What term is used to describe the cytoplasm of a muscle fiber?

    <p>Sarcoplasm</p> Signup and view all the answers

    Which component is responsible for transmitting signals at the neuromuscular junction?

    <p>Motor neurons</p> Signup and view all the answers

    What is the maximum diameter range of a muscle fiber?

    <p>10 μ to 100 μ</p> Signup and view all the answers

    What is the structural function of a tendon in relation to muscle?

    <p>Attaching muscle to bone</p> Signup and view all the answers

    What is the electrical potential in muscle during resting conditions called?

    <p>Resting membrane potential</p> Signup and view all the answers

    Which phase of action potential involves the inside of the muscle becoming positive?

    <p>Depolarization</p> Signup and view all the answers

    At what membrane potential is the human skeletal muscle's resting membrane potential typically observed?

    <p>-90 mV</p> Signup and view all the answers

    What occurs during the repolarization phase of action potential?

    <p>Muscle returns to resting membrane potential</p> Signup and view all the answers

    What happens when the firing level of depolarization is reached?

    <p>Na+ channels activate rapidly leading to overshoot</p> Signup and view all the answers

    What is the role of voltage gated Na+ and K+ channels in action potential?

    <p>They facilitate the influx and efflux of ions during depolarization and repolarization</p> Signup and view all the answers

    What is a characteristic of the polarized state of muscle fibers?

    <p>Inside is negative and outside is positive</p> Signup and view all the answers

    What initiates the depolarization phase of action potential?

    <p>Slow influx of Na+ ions through voltage gated channels</p> Signup and view all the answers

    What is the primary function of the neuromuscular junction?

    <p>To facilitate communication between nerve and muscle fibers</p> Signup and view all the answers

    What neurotransmitter is primarily released at the neuromuscular junction?

    <p>Acetylcholine</p> Signup and view all the answers

    What structure is formed at the site where the axon terminal meets the muscle fiber?

    <p>Motor endplate</p> Signup and view all the answers

    Which enzyme is responsible for breaking down acetylcholine in the synaptic cleft?

    <p>Acetylcholinesterase</p> Signup and view all the answers

    What triggers the release of acetylcholine at the axon terminal?

    <p>Inflow of calcium ions</p> Signup and view all the answers

    What is the significance of the thickened membrane below the motor endplate?

    <p>It contains receptors for neurotransmitter binding</p> Signup and view all the answers

    What occurs when acetylcholine binds to nicotinic receptors on the postsynaptic membrane?

    <p>Ligand-gated sodium channels open, increasing permeability to sodium</p> Signup and view all the answers

    Which statement accurately describes the endplate potential?

    <p>It represents a temporary increase in resting membrane potential to –60 mV.</p> Signup and view all the answers

    Which of the following components is NOT part of the neuromuscular junction?

    <p>Arachnoid membrane</p> Signup and view all the answers

    What initiates muscle contraction at the neuromuscular junction?

    <p>Binding of acetylcholine to nicotinic receptors</p> Signup and view all the answers

    What characterizes a miniature endplate potential?

    <p>It has an amplitude of approximately 0.5 mV.</p> Signup and view all the answers

    What happens during repolarization at the neuromuscular junction?

    <p>Efflux of potassium ions out of the cell</p> Signup and view all the answers

    What is the resting membrane potential at the neuromuscular junction before stimulation?

    <p>-90 mV</p> Signup and view all the answers

    How many vesicles approximately release acetylcholine at a time during neuromuscular transmission?

    <p>300 vesicles</p> Signup and view all the answers

    What is the main function of acetylcholine at the neuromuscular junction?

    <p>To initiate depolarization in the postsynaptic membrane</p> Signup and view all the answers

    What happens to acetylcholine after it has acted on the postsynaptic membrane?

    <p>It is destroyed to terminate its action.</p> Signup and view all the answers

    Study Notes

    Muscle Physiology

    • Muscle mass is surrounded by fascia, a thick fibrous tissue layer.
    • Beneath the fascia, muscle tissue is covered by a connective tissue sheath called the epimysium.
    • Muscle fibers are grouped into bundles or fasciculi, each covered by perimysium.
    • Individual muscle fibers are enclosed by the endomysium, a connective tissue layer.
    • Muscle fibers are attached to bone via tendons.
    • The plasma membrane, called the sarcolemma, encloses each muscle fiber.
    • Sarcoplasm, the cytoplasm within the muscle fiber, contains:
      • Nuclei
      • Myofibrils
      • Golgi apparatus
      • Mitochondria
      • Sarcoplasmic reticulum
      • Ribosomes
      • Glycogen droplets
      • Lipid droplets

    Myofibrils

    • Myofibrils are fine parallel filaments present in the sarcoplasm.
    • They run the entire length of the muscle fiber.
    • Myofibrils appear as small dots in cross-sections of muscle fibers.
    • The diameter of a myofibril is 0.2 to 2 μm.
    • Myofibril length varies between 1 cm and 4 cm, depending on the muscle fiber length.

    Microscopic Structure of a Myofibril

    • Myofibrils consist of alternating light (I) bands and dark (A) bands, formed by muscle proteins.

    Electrical Changes During Muscular Contraction

    • Muscle fibers exhibit electrical changes in both resting and active states.
    • Resting membrane potential is the electrical potential difference across the cell membrane at rest.
    • The muscle fiber is negative inside and positive outside during resting membrane potential, a state called polarization.
    • The resting membrane potential of human skeletal muscle is -90 mV.

    Action Potential

    • Action potential is a series of electrical changes in the membrane potential when a muscle or nerve is stimulated.
    • Action potential occurs in two phases:
      • Depolarization: Inside of the muscle becomes positive and outside becomes negative, abolishing the polarized state.
      • Repolarization: The muscle returns to its resting membrane potential, with the inside becoming negative and outside positive.

    Ionic Basis of Action Potential

    • Voltage-gated Na+ channels and K+ channels are crucial for action potential development.
    • During depolarization, Na+ channels open, leading to a slow influx of Na+.
    • At a depolarization of 7 to 10 mV, Na+ channels open rapidly, causing Na+ influx.
    • The Na+ influx leads to an overshoot, but is short-lived due to Na+ channel inactivation.
    • Simultaneously, K+ channels open, causing K+ efflux and repolarization.

    Neuromuscular Junction

    • The neuromuscular junction is the connection between a nerve fiber terminal branch and a muscle fiber.
    • Skeletal muscle fibers are innervated by motor nerve fibers.
    • Each motor nerve fiber (axon) branches into many terminal branches, each innervating a single muscle fiber at a neuromuscular junction.

    Axon Terminal and Motor Endplate

    • The terminal branch of the nerve fiber is called the axon terminal.
    • The axon loses its myelin sheath when it approaches the muscle fiber.
    • The exposed axis cylinder expands into a bulb called the motor endplate.
    • Axon terminals contain mitochondria and synaptic vesicles, which hold the neurotransmitter, acetylcholine (Ach).
    • Ach is synthesized by mitochondria and stored in vesicles.

    Synaptic Trough or Gutter

    • The motor endplate invaginates into the muscle fiber, forming a depression called the synaptic trough or gutter.
    • The muscle fiber membrane below the motor endplate is thickened.

    Synaptic Cleft

    • The nerve ending membrane is the presynaptic membrane.
    • The muscle fiber membrane is the postsynaptic membrane.
    • The space between these membranes is the synaptic cleft, which contains basal lamina.
    • Acetylcholinesterase (AchE), an enzyme, is attached to the basal lamina.

    Subneural Clefts

    • The postsynaptic membrane of the muscle fiber forms numerous folds called subneural clefts.
    • The postsynaptic membrane contains nicotinic acetylcholine receptors.

    Neuromuscular Transmission

    • Neuromuscular transmission is the transfer of information from the motor nerve ending to the muscle fiber via the neuromuscular junction.
    • This mechanism initiates muscle contraction.

    Events of Neuromuscular Transmission

    • A series of events occur at the neuromuscular junction:
      • Release of acetylcholine
      • Action of acetylcholine
      • Development of endplate potential
      • Development of miniature endplate potential
      • Destruction of acetylcholine

    Release of Acetylcholine

    • Action potentials reaching the axon terminal open voltage-gated calcium channels.
    • Calcium ions flow into the axon terminal.
    • Calcium causes synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine by exocytosis.
    • Each vesicle contains around 10,000 acetylcholine molecules, and approximately 300 vesicles release acetylcholine at a time.

    Action of Acetylcholine

    • Acetylcholine, released into the synaptic cleft binds to nicotinic receptors on the postsynaptic membrane.
    • This binding increases the permeability of the postsynaptic membrane to sodium, opening ligand-gated sodium channels.
    • Sodium ions enter the neuromuscular junction through these channels, altering the resting membrane potential and creating the endplate potential.

    Development of Endplate Potential

    • Endplate potential is the change in resting membrane potential when an impulse reaches the neuromuscular junction.
    • The resting membrane potential at the neuromuscular junction is -90 mV.
    • Sodium influx causes slight depolarization, reaching -60 mV, called the endplate potential.

    Development of Miniature Endplate Potential

    • Miniature endplate potential is a weak endplate potential caused by the release of a small amount of acetylcholine.
    • Each quantum of acetylcholine produces a weak miniature endplate potential.
    • The amplitude of this potential is only up to 0.5 mV.
    • Miniature endplate potential cannot produce action potential in the muscle.
    • Continuous release of multiple quanta of acetylcholine leads to action potential in the muscle.

    Destruction of Acetylcholine

    • Acetylcholine in the synaptic cleft is rapidly destroyed (within one millisecond) by the enzyme acetylcholinesterase.
    • The short duration is sufficient to excite the muscle fiber.
    • Rapid destruction prevents repeated excitation and allows muscle relaxation.

    Reuptake Process

    • Reuptake is a process where degraded neurotransmitter products are taken back into the presynaptic axon terminal for reuse.
    • Acetylcholinesterase breaks down acetylcholine into choline and acetate.
    • Choline is retaken into the axon terminal and reused to synthesize new acetylcholine.

    Excitation-Contraction Coupling in Skeletal Muscle

    • Excitation-contraction coupling is the sequence of events that link nerve fiber stimulation to skeletal muscle fiber contraction.

    Motor Unit

    • A motor unit consists of a single motor neuron, its axon terminals, and the muscle fibers it innervates.
    • A motor neuron activates a group of muscle fibers through its axon terminals.
    • Stimulation of a motor neuron causes contraction of all the muscle fibers it innervates.

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    Muscle Physiology PDF

    Description

    Test your knowledge on muscle physiology by exploring the structure and function of muscle tissues. This quiz covers essential topics such as the layers of connective tissue, muscle fibers, and myofibrils. Challenge yourself and see how well you understand this crucial aspect of biology!

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