Muscle Physiology: Excitation-Contraction Coupling
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Questions and Answers

What is the primary neurotransmitter released by postganglionic neurons in the sympathetic nervous system?

  • Dopamine
  • Serotonin
  • Acetylcholine
  • Noradrenaline (correct)

    • Which response is predominantly associated with stimulation of the sympathetic nervous system?

  • Inhibits heart rate
  • Increases metabolic function
  • Accelerates digestion
  • Relaxes airways (correct)

    • Which of the following functions is primarily governed by the parasympathetic nervous system?

  • Increasing peripheral resistance
  • Digesting food (correct)
  • Accelerating heart rate
  • Relaxing airways

    • What role does acetylcholine play in the sympathetic nervous system?

    <p>Released by preganglionic neurons</p> Signup and view all the answers

    What is a likely outcome of administering adrenaline during a cardiac arrest?

    <p>Inhibits digestion</p> Signup and view all the answers

    What occurs during relaxation in muscle contraction?

    <p>Decrease in Ca2+ or ATP levels</p> Signup and view all the answers

    What is the primary mechanism that increases muscle contraction strength?

    <p>Recruitment of additional motor units</p> Signup and view all the answers

    Which statement correctly describes a reflex action?

    <p>It is an involuntary movement not requiring the brain</p> Signup and view all the answers

    What role do interneurons play in reflex actions?

    <p>They facilitate communication between sensory and motor neurons</p> Signup and view all the answers

    How do the muscles work during reflex actions to maintain stability?

    <p>Through coordinated activity of flexors and extensors</p> Signup and view all the answers

    What role does calcium ion (Ca2+) play in the process of muscle contraction?

    <p>It binds to troponin, allowing myosin binding sites on actin to be exposed.</p> Signup and view all the answers

    Which statement best describes the sequence of events at the neuromuscular junction during muscle contraction?

    <p>The presynaptic action potential leads to ACh release, causing postsynaptic depolarization.</p> Signup and view all the answers

    What is the primary function of the sarcoplasmic reticulum in muscle fibers?

    <p>To store calcium ions required for muscle contraction.</p> Signup and view all the answers

    Which of the following accurately describes the relationship between motor neurons and muscle fibers?

    <p>Multiple muscle fibers can be activated by a single motor neuron.</p> Signup and view all the answers

    What initiates the sliding filament mechanism during muscle contraction?

    <p>Release of calcium ions from the sarcoplasmic reticulum.</p> Signup and view all the answers

    What is the role of acetylcholine (ACh) in muscle contraction?

    <p>It binds to receptors on the muscle fiber’s sarcolemma, triggering depolarization.</p> Signup and view all the answers

    What occurs directly after the postsynaptic depolarization in the muscle fiber?

    <p>Calcium ions are released from the sarcoplasmic reticulum.</p> Signup and view all the answers

    What happens to myosin after it binds to actin during muscle contraction?

    <p>The myosin head pivots, pulling the actin filament toward the center of the sarcomere.</p> Signup and view all the answers

    What is a direct consequence of the parasympathetic nervous system activating acetylcholine receptors?

    <p>Constricted airways</p> Signup and view all the answers

    Which statement correctly describes the function of somatic motor neurons?

    <p>They generate behavior through voluntary control of skeletal muscles.</p> Signup and view all the answers

    How are lower motor neurons organized within the ventral horn of the spinal cord?

    <p>Neurons for axial muscles are more medial than distal muscle neurons.</p> Signup and view all the answers

    What describes the relationship between alpha motor neurons and muscle fibers?

    <p>One alpha motor neuron can synapse with many muscle fibers.</p> Signup and view all the answers

    What is a key characteristic of the motor neuron pool?

    <p>It consists of all motor neurons innervating one muscle.</p> Signup and view all the answers

    What role do lower motor neurons play in muscle contraction?

    <p>They initiate contraction by interacting with local spinal cord circuits.</p> Signup and view all the answers

    Which statement is true regarding the contraction of large versus small muscles?

    <p>Large motor neurons ensure more significant force generation for large muscles.</p> Signup and view all the answers

    What is the main effect of the housekeeping function of action potentials in parasympathetic neurons?

    <p>They enable long-distance propagation of action potentials.</p> Signup and view all the answers

    Study Notes

    Excitation-Contraction Coupling and Reflexes

    • Excitation-Contraction Coupling:

      • Muscle contraction is initiated by the sliding of actin filaments along myosin filaments.
      • Calcium ions bind to troponin, exposing sites on actin for myosin binding.
      • Myosin heads then bind to actin and complete a power stroke to move actin filaments.
      • Myosin releases actin when ATP is used.

    • Muscle Contraction:

      • Action potential travels along the alpha motor neuron.
      • Acetylcholine (ACh) is released and binds to receptors on the muscle fiber.
      • Depolarization of muscle fiber occurs.
      • Calcium ions are released from the sarcoplasmic reticulum.
      • Calcium ions bind to troponin, initiating the sliding filament mechanism.
      • Actin filaments slide along myosin filaments.
      • Muscle contraction occurs.
      • Muscle relaxation occurs when calcium levels return to normal.

    • Motor Units:

      • A motor unit consists of a motor neuron and all the muscle fibers it innervates.
      • Small motor units control fine movements, large motor units control powerful movements.
      • The motor neuron pool is the collection of alpha motor neurons that activate a single muscle.

    • Single Muscle Twitches:

      • A single twitch is the response of a muscle to a single action potential.
      • Sustained contractions result from repeated action potentials from motor units.
      • Increased firing rate of motor neurons increases the strength of contraction.
      • Multiple motor units firing in succession increase contraction further.

    • Reflexes:

      • Reflexes are involuntary responses to stimuli.
      • Stretch reflexes involve reciprocal innervation of flexor and extensor muscles.
      • Knee-jerk reflex is an example of a stretch reflex.
      • Crossed-extensor reflex coordinates movement in response to painful stimuli.

    • Neurotransmitter Release at Neuromuscular Junctions:

      • Muscle contraction is initiated by the release of acetylcholine.
      • Acetylcholine binds to receptors on the postsynaptic muscle fiber.
      • One pre-synaptic action potential is sufficient to induce a postsynaptic action potential.

    • Structure of a Muscle Fiber:

      • Sarcolemma: cell membrane surrounding the muscle fiber.
      • Myofibrils: contractile units in the muscle fiber.
      • Sarcoplasmic reticulum: stores calcium ions.

    • Molecular Basis of Excitation-Contraction Coupling:

      • Organization of the components involved in muscle contraction.

    • Vestibulo-ocular Reflex (VOR):

      • Coordinated movement of eye muscles to maintain stable vision during head movement.
      • Sensory input from the vestibular system, signal to muscles, muscles contract to maintain vision.

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    Excitation-Contraction Coupling and Reflexes PDF

    Description

    Explore the intricate processes of excitation-contraction coupling and reflexes in muscle physiology. This quiz covers key concepts including muscle contraction, action potential, and the role of calcium and motor units. Test your knowledge on how muscle fibers respond and relax in response to signals.

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