Neuroscience Chapter on Action Potentials
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Questions and Answers

What is the main function of the refractory period in nerve fibers?

  • It ensures impulses flow in both directions.
  • It limits the rate of impulses to 500-1000 per second. (correct)
  • It increases the rate of impulses along a fiber.
  • It enhances the resting potential of the fiber.
  • What happens during the absolute refractory period?

  • The nerve fiber can be restimulated by a weaker stimulus.
  • It is impossible to restimulate the fiber. (correct)
  • The sodium ion channels are completely open.
  • The axon can conduct impulses in either direction.
  • What is primarily responsible for restoring the resting potential after an action potential?

  • Sodium/potassium pump and membrane permeability to potassium ions. (correct)
  • Chloride ions and their influx.
  • Calcium ions and their channels.
  • Magnesium ions and their diffusion.
  • What initiates the wave of depolarization in a neurone?

    <p>The diffusion of sodium ions into the neurone.</p> Signup and view all the answers

    In what time frame does the absolute refractory period occur?

    <p>Immediately after the action potential.</p> Signup and view all the answers

    What characterizes the relative refractory period?

    <p>A stronger stimulus is needed to re-stimulate the axon.</p> Signup and view all the answers

    What does the recovery time of an axon refer to?

    <p>The refractory period.</p> Signup and view all the answers

    How does the refractory period affect impulse direction along nerves?

    <p>It ensures impulses flow in only one direction.</p> Signup and view all the answers

    What triggers the opening of sodium ion channels in the next region of the neurone?

    <p>The diffusion of sodium ions from the previous region.</p> Signup and view all the answers

    What happens to the permeability of the axon membrane during depolarization?

    <p>It increases specifically to sodium ions.</p> Signup and view all the answers

    What is the potential difference across the membrane at the peak of the action potential?

    <p>+40 mV</p> Signup and view all the answers

    What occurs immediately after depolarization in the action potential process?

    <p>Potassium ions rapidly diffuse out of the axon.</p> Signup and view all the answers

    What defines the threshold for triggering an action potential?

    <p>The opening of sufficient sodium ion channels.</p> Signup and view all the answers

    What is the duration of the depolarization phase in the action potential?

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

    What is the typical shape of the oscilloscope trace during an action potential referred to as?

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

    Why do potassium ions diffuse out of the axon during repolarization?

    <p>They are repelled by the positive charge inside the axon.</p> Signup and view all the answers

    What mechanism restores the resting potential after an action potential?

    <p>Pumping of excess sodium ions out of the axon.</p> Signup and view all the answers

    Which of the following statements about the action potential is incorrect?

    <p>The action potential can vary in amplitude based on the stimulus.</p> Signup and view all the answers

    During which phase does the inside of the axon become negative relative to the outside again?

    <p>Repolarization phase</p> Signup and view all the answers

    Study Notes

    Action Potential Overview

    • Impulse along an axon changes cell membrane permeability to sodium ions due to stimuli or neurotransmitters.
    • Experimental stimulation often involves controlled electrical impulses.

    Depolarization Phase

    • Stimulation increases axon membrane's permeability to sodium ions.
    • Sodium ion channels open, allowing rapid diffusion of sodium ions, reversing membrane potential briefly.
    • Depolarization lasts approximately 1 millisecond, peaking at about +40mV, known as the action potential.
    • This process occurs in all nerve fibers, not just axons.

    Repolarization Phase

    • Sodium channels close post-depolarization; excess sodium is pumped out.
    • Voltage-dependent potassium channels open, allowing potassium ions to diffuse out.
    • Inside of the axon becomes negatively charged again, restoring the resting potential over a few milliseconds.

    Action Potential Recording

    • Action potentials can be recorded with an internal/external electrode setup using an oscilloscope.
    • Oscilloscope trace appears as a 'spike', illustrating potential differences during sodium influx and resting potential recovery.

    Threshold and All-or-Nothing Response

    • Threshold is reached when sufficient sodium channels open, allowing sodium influx to surpass potassium outflow.
    • The action potential is an all-or-nothing response; its magnitude remains consistent regardless of stimulus strength.

    Refractory Period

    • Crucial for nervous system function, limiting impulse flow to 500-1000 per second and ensuring unidirectional impulse propagation.
    • The refractory period includes two phases:
      • Absolute refractory period: Initial phase post-action potential where restimulation is impossible due to blocked sodium channels.
      • Relative refractory period: Occurs after absolute, where stronger stimuli are needed for re-stimulation.

    Propagation of Action Potential

    • Action potential spreads along the neuron as a wave of depolarization:
      • Sodium ions entering cause adjacent sodium channels to open.
      • This initiates sodium influx in nearby regions, creating a continuous wave.
      • The wave moves away from refractory membrane areas that cannot initiate new action potentials.

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    Description

    Explore the mechanisms of action potentials in neurons, including the depolarization and repolarization phases. Understand how sodium and potassium ions play a crucial role in this electrical signaling process. This quiz will test your knowledge of neuronal impulse transmission and its physiological implications.

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