The Action Potential
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Questions and Answers

What is the primary reason for the opening of sodium channels in the membrane during the initiation of an action potential?

  • The concentration gradient for sodium is higher inside the cell than outside the cell.
  • The electrical gradient attracts the sodium ion.
  • The potassium ion concentration is higher inside the cell than outside the cell.
  • The concentration gradient for sodium is higher outside the cell than inside the cell. (correct)

    • What is the term for the change in membrane potential when it moves towards zero?

  • Repolarization
  • Electrical gradient
  • Hyperpolarization
  • Depolarization (correct)

    • What is the approximate voltage of the resting membrane potential?

  • -90 mV
  • -50 mV
  • -70 mV (correct)
  • -30 mV

    • What is the function of voltage-gated potassium channels during the repolarization phase?

    <p>Allow potassium ions to leave the cell</p> Signup and view all the answers

    Why does the sodium cation continue to enter the cell even after the membrane potential has become zero?

    <p>The concentration gradient for sodium is strong</p> Signup and view all the answers

    What is the term for the movement of the membrane potential back towards its resting voltage?

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

    What is the approximate voltage reached by the membrane potential during the action potential?

    <p>+30 mV</p> Signup and view all the answers

    What happens to the membrane potential after repolarization?

    <p>It overshoots the resting potential</p> Signup and view all the answers

    What is the minimum voltage required to reach the threshold of an action potential?

    <p>-55 mV</p> Signup and view all the answers

    What is the function of the inactivation gate of the voltage-gated Na+ channel?

    <p>To close after a specific period of time</p> Signup and view all the answers

    What occurs during the hyperpolarizing overshoot?

    <p>K+ leaves the cell, causing the membrane potential to become more negative</p> Signup and view all the answers

    Why does a stronger stimulus not make a 'bigger' action potential?

    <p>Because action potentials are 'all or none'</p> Signup and view all the answers

    What is the function of the voltage-gated K+ channel?

    <p>To regulate the flow of K+ out of the cell</p> Signup and view all the answers

    What happens during the absolute refractory period?

    <p>Another action potential will not start</p> Signup and view all the answers

    What is the duration of an action potential?

    <p>Approximately 2 milliseconds</p> Signup and view all the answers

    What is the voltage at which the voltage-gated K+ channel opens?

    <p>-50 mV</p> Signup and view all the answers

    What happens to the voltage-gated Na+ channel during repolarization?

    <p>No more sodium can enter the cell</p> Signup and view all the answers

    Why does a stronger stimulus initiate multiple action potentials more quickly?

    <p>Because the threshold is reached more quickly</p> Signup and view all the answers

    What causes the membrane potential to return to its resting voltage after hyperpolarization?

    <p>The efflux of K+ ions</p> Signup and view all the answers

    What is the name of the voltage at which voltage-gated Na+ channels open?

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

    Which of the following statements accurately describes the action potential?

    <p>A brief, all-or-nothing electrical signal</p> Signup and view all the answers

    What is the main difference between the driving force for Na+ and K+ during an action potential?

    <p>Na+ is driven into the cell, while K+ is driven out of the cell</p> Signup and view all the answers

    What is the role of the voltage-gated Na+ channels in initiating an action potential?

    <p>They open when the membrane potential reaches threshold</p> Signup and view all the answers

    Which of the following is NOT a type of Na+ channel that can contribute to depolarization?

    <p>Calcium-gated Na+ channel</p> Signup and view all the answers

    What happens if a stimulus does not depolarize the membrane to -55 mV or higher?

    <p>The membrane potential will remain at resting voltage</p> Signup and view all the answers

    What is the significance of the threshold in the context of action potential generation?

    <p>It determines whether an action potential will be generated</p> Signup and view all the answers

    What is the term used to describe the period after an action potential when the membrane potential is more negative than the resting potential?

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

    How does the action potential differ from the charge stored in a battery?

    <p>The action potential is a much smaller change in voltage</p> Signup and view all the answers

    Study Notes

    The Action Potential

    • The resting membrane potential is the steady state of the cell, which is a dynamic process balanced by ion leakage and ion pumping.
    • To get an electrical signal started, the membrane potential has to change, which starts with a channel opening for Na+ in the membrane.
    • The concentration of Na+ is higher outside the cell than inside the cell by a factor of 10, causing ions to rush into the cell driven largely by the concentration gradient.
    • The sodium ion entering the cell will cause the membrane potential to become less negative, known as depolarization, moving toward zero.

    Depolarization and Repolarization

    • The concentration gradient for Na+ is so strong that it will continue to enter the cell even after the membrane potential has become zero, so that the voltage immediately around the pore begins to become positive.
    • The electrical gradient also plays a role, as negative proteins below the membrane attract the sodium ion.
    • As the membrane potential reaches +30 mV, other voltage-gated channels open in the membrane, specific for the potassium ion.
    • A concentration gradient acts on K+, and as K+ starts to leave the cell, taking a positive charge with it, the membrane potential begins to move back toward its resting voltage, known as repolarization.
    • Repolarization returns the membrane potential to the -70 mV value that indicates the resting potential, but it actually overshoots that value, resulting in hyperpolarization.

    Characteristics of the Action Potential

    • The action potential is the electrical signal that nervous tissue generates for communication.
    • The change in the membrane voltage from -70 mV at rest to +30 mV at the end of depolarization is a 100-mV change.
    • The membrane potential can be described as a battery, with a charge stored across the membrane that can be released under the correct conditions.

    Initiation of the Action Potential

    • The description above conveniently glosses over the initiation of the action potential, which is vital to understanding what is happening.
    • The membrane potential will stay at the resting voltage until something changes, such as a Na+ channel opening.
    • There are a few different types of channels that allow Na+ to cross the membrane, including ligand-gated Na+ channels, mechanically gated Na+ channels, and voltage-gated Na+ channels.
    • A stimulus, such as a neurotransmitter binding to its receptor protein or a sensory stimulus activating a sensory receptor cell, gets the process started.

    Threshold and the All-or-None Principle

    • The threshold is the voltage at which the voltage-gated Na+ channels open, which is -55 mV.
    • Any depolarization that does not change the membrane potential to -55 mV or higher will not reach threshold and thus will not result in an action potential.
    • If the threshold is reached, then the action potential continues and runs all the way to +30 mV, at which K+ causes repolarization, including the hyperpolarizing overshoot.
    • The action potential is an all-or-none event, meaning that either the membrane reaches the threshold and everything occurs as described above, or the membrane does not reach the threshold and nothing else happens.

    Refractory Period

    • While an action potential is in progress, another one cannot be initiated, which is referred to as the refractory period.
    • There are two phases of the refractory period: the absolute refractory period and the relative refractory period.
    • During the absolute phase, another action potential will not start, and during the relative phase, a new action potential could be started, but only by a stronger stimulus than the one that initiated the current action potential.

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    Description

    Learn about the dynamic process of resting membrane potential and how it changes to generate an electrical signal, involving ion leakage, pumping and channel opening for sodium ions.

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