Action Potential Overview and Channels
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Questions and Answers

What occurs during the action potential in a neuron?

  • The membrane potential remains constant.
  • The membrane rapidly depolarizes and repolarizes. (correct)
  • Only sodium channels are involved.
  • Potassium channels open before sodium channels.

    • What is the resting membrane potential typically around?

  • -50 mV
  • -70 mV (correct)
  • 0 mV
  • -90 mV

    • What happens to sodium channels after they open during membrane depolarization?

  • They remain open indefinitely.
  • They only open again at hyperpolarized potentials.
  • They become inactive and cannot be reopened until the resting potential is restored. (correct)
  • They close immediately without any inactivation.

    • What characterizes the 'All-or-None Law' in action potentials?

    <p>Only a threshold stimulus generates a complete action potential. (C)</p> Signup and view all the answers

    What role does the voltage-gated potassium channel play during an action potential?

    <p>It opens after sodium channels to help repolarize the membrane. (D)</p> Signup and view all the answers

    When does the inactivation gate of a sodium channel reopen?

    <p>When the membrane returns to or near the resting potential. (D)</p> Signup and view all the answers

    What initiates the generation of an action potential?

    <p>A threshold stimulus is reached. (C)</p> Signup and view all the answers

    How do voltage-gated sodium channels respond to changes in membrane voltage?

    <p>They respond quickly, opening before potassium channels. (C)</p> Signup and view all the answers

    What determines the strength of a stimulus in terms of action potentials?

    <p>The frequency of action potentials (D)</p> Signup and view all the answers

    During which period is the axon membrane unable to respond to any subsequent stimuli, regardless of their strength?

    <p>Absolute refractory period (D)</p> Signup and view all the answers

    What type of stimulus is required to generate a second action potential during the relative refractory period?

    <p>A strong depolarization stimulus (D)</p> Signup and view all the answers

    What is the impact of the myelin sheath on the ion flow through the membrane?

    <p>It decreases ion flow through the membrane (D)</p> Signup and view all the answers

    Why is saltatory conduction faster in myelinated fibers compared to nonmyelinated fibers?

    <p>Less charge leaks out in myelinated sections (B)</p> Signup and view all the answers

    Where do action potentials occur in myelinated axons?

    <p>At the nodes of Ranvier (A)</p> Signup and view all the answers

    How much can the velocity of nerve transmission increase due to saltatory conduction in myelinated fibers?

    <p>5 to 50-fold (C)</p> Signup and view all the answers

    What characteristic of myelinated axons contributes to less resistance in the spread of charges?

    <p>They are generally thicker than unmyelinated axons (B)</p> Signup and view all the answers

    Flashcards

    Stimulus strength coding

    The strength of a stimulus is coded by the frequency of action potentials, not their amplitude.

    Absolute Refractory Period

    A period after an action potential where the neuron cannot respond to any stimulus (no matter how strong).

    Relative Refractory Period

    A period after an action potential where a stronger-than-usual stimulus is needed to trigger another action potential.

    Saltatory Conduction

    Action potential propagation in myelinated axons; jumping from node to node.

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    Myelin Sheath

    Insulating layer around some axons that speeds up action potential propagation.

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    Nodes of Ranvier

    Gaps in the myelin sheath where action potentials are generated in myelinated axons.

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    Action Potential Propagation

    The movement of an action potential down an axon.

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    Conduction Speed in Myelinated vs. Non-Myelinated Axons

    Myelinated axons propagate action potentials significantly faster than non-myelinated axons, due to saltatory conduction.

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    Action Potential (AP)

    A rapid change in membrane potential where the cell membrane quickly depolarizes and then repolarizes.

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    Voltage-Gated Sodium Channel

    A protein channel in the cell membrane that opens in response to a change in voltage, allowing sodium ions (Na+) to flow into the cell.

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    Sodium Channel Activation

    The opening of the voltage-gated sodium channel, allowing sodium ions (Na+) to flow into the cell.

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    Sodium Channel Inactivation

    A temporary closing of the voltage-gated sodium channel, preventing further sodium flow.

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    Voltage-Gated Potassium Channel

    A protein channel in the cell membrane that opens in response to a change in voltage, allowing potassium ions (K+) to flow out of the cell.

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    Threshold

    The minimum level of depolarization required to trigger an action potential.

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    All-or-None Law

    An action potential either occurs with full strength or not at all; its strength does not vary with the strength of the stimulus.

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    Na+-K+ ATPase

    A protein pump that actively transports sodium ions (Na+) out of the cell and potassium ions (K+) into the cell, maintaining the resting membrane potential.

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    Study Notes

    Action Potential Overview

    • Action potentials are rapid changes in membrane potential characterized by depolarization and repolarization.
    • Action potentials are triggered when the membrane potential reaches a threshold.
    • The rapid depolarization phase involves sodium ions entering the cell.
    • Repolarization involves potassium ions leaving the cell.
    • The after-hyperpolarization phase occurs as potassium channels slowly close.
    • An action potential is an 'all-or-none' phenomenon; the size of the response does not vary with the strength of the stimulus.

    Voltage-Gated Sodium Channels

    • Voltage-gated sodium channels have two gates: activation and inactivation gates.
    • Activation gates open rapidly in response to depolarization.
    • Inactivation gates close slowly after the activation gate opens.
    • Sodium channels become inactivated at a certain membrane potential.
    • Channels cannot be opened by depolarization while inactivated.

    Voltage-Gated Potassium Channels

    • Voltage-gated potassium channels open more slowly than sodium channels in response to depolarization.
    • Outward current through open potassium channels repolarizes the membrane.
    • Potassium channels close slowly, contributing to the after-hyperpolarization phase.

    Refractory Periods

    • Absolute refractory period: No stimulus can elicit another action potential, Na+ channels inactivated.
    • Relative refractory period: A stronger-than-normal stimulus can elicit an action potential, K+ channels still open.
    • The refractory periods help to ensure unidirectional propagation of action potentials.

    Action Potential Propagation

    • Local currents depolarize adjacent regions, causing voltage-gated sodium channels to open.
    • Action potentials propagate along the axon in a chain reaction.
    • Myelinated axons have gaps in the myelin sheath, known as Nodes of Ranvier, where voltage-gated sodium channels are concentrated.
    • Action potentials jump between nodes, called saltatory conduction, which speeds up propagation compared to unmyelinated axons.

    Inhibition of Excitability

    • Local anesthetics prevent action potentials by binding to voltage-gated sodium channels.
    • This prevents sodium ions from flowing into the cell and inhibits depolarization.

    Plateau in Some Action Potentials

    • Some action potentials demonstrate a plateau phase, often seen in cardiac muscle.
    • This phase involves a mix of voltage-gated calcium and sodium channels, contributing to sustained depolarization.

    Rhythmic Activity

    • Some tissues exhibit rhythmic activity, creating action potentials repetitively.
    • This rhythm is often controlled by specific ion currents and the interactions of voltage-gated ion channels.

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    Related Documents

    Lecture 6 - Physiology PDF

    Description

    This quiz explores the dynamics of action potentials and the roles of voltage-gated sodium and potassium channels. Test your knowledge on the phases of action potentials, the all-or-none principle, and the mechanisms governing sodium and potassium channels. Perfect for students in neurobiology or physiology courses.

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