Refractory Periods in Action Potentials
40 Questions
1 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What characterizes the absolute refractory period?

  • Action potentials can be triggered with a strong stimulus.
  • Na⁺ channels are fully open during this period.
  • It overlaps with the entire duration of the action potential. (correct)
  • It occurs only after the relative refractory period.

    • What is the primary basis for the absolute refractory period?

  • Hyperpolarization of the membrane.
  • Closure of the inactivation gates of the Na⁺ channel. (correct)
  • Activation of Ca²⁺ channels.
  • Increased permeability to K⁺.

    • How does the relative refractory period differ from the absolute refractory period?

  • A greater stimulus is required for action potential initiation in the relative refractory period. (correct)
  • It occurs simultaneously with an action potential.
  • No action potential can be generated during both periods.
  • It lasts longer than the absolute refractory period.

    • What happens during accommodation in nerve or muscle cells?

    <p>The threshold potential may pass without firing an action potential.</p> Signup and view all the answers

    What is the consequence of elevated serum K⁺ concentration on resting membrane potential?

    <p>Depolarization of the resting membrane.</p> Signup and view all the answers

    During which phase can an action potential be elicited with a greater than usual inward current?

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

    What physiological change occurs when depolarization happens slowly?

    <p>Inactivation gates of Na⁺ channels close.</p> Signup and view all the answers

    Which factor is primarily responsible for the need for a greater inward current during the relative refractory period?

    <p>Higher K⁺ conductance than at rest.</p> Signup and view all the answers

    What occurs during the repolarization phase of the action potential?

    <p>Na⁺ channels close, and K⁺ channels open.</p> Signup and view all the answers

    What is the main role of the inactivation gates of the Na⁺ channel during action potential generation?

    <p>To prevent further action potentials during the absolute refractory period.</p> Signup and view all the answers

    What is the relationship between nerve diameter and internal resistance?

    <p>Internal resistance is inversely proportional to diameter</p> Signup and view all the answers

    How does increasing the size of a nerve fiber affect the length constant?

    <p>The length constant increases as nerve size increases</p> Signup and view all the answers

    What role does myelin play in conduction velocity?

    <p>It acts as a lipid insulator to increase membrane resistance</p> Signup and view all the answers

    What is the effect of decreased membrane capacitance on action potentials?

    <p>It hastens the response to inward currents</p> Signup and view all the answers

    Why is it important for the myelin sheath to have breaks?

    <p>To enable action potentials at nodes of Ranvier</p> Signup and view all the answers

    What occurs at the nodes of Ranvier in myelinated nerve fibers?

    <p>Current can flow across the membrane and action potentials can occur</p> Signup and view all the answers

    What effect does having a smaller internal resistance (Rᵢ) have on the conduction of action potentials?

    <p>It aids in the propagation of action potentials over longer distances</p> Signup and view all the answers

    What happens if a nerve is fully myelinated?

    <p>There would be no conduction of action potentials</p> Signup and view all the answers

    What is the primary effect of myelination on membrane capacitance?

    <p>Decreases capacitance and speeds up conduction</p> Signup and view all the answers

    Which factor does NOT contribute to increased conduction velocity in nerves?

    <p>Decreased axon length</p> Signup and view all the answers

    What happens to the Na⁺ channels during sustained depolarization?

    <p>They close their inactivation gates.</p> Signup and view all the answers

    What initiates an action potential in a nerve axon?

    <p>Depolarization in the initial segment of the axon.</p> Signup and view all the answers

    How does local current contribute to action potential propagation?

    <p>It causes adjacent regions to depolarize to threshold.</p> Signup and view all the answers

    What occurs at the peak of an action potential?

    <p>The polarity of the membrane potential reverses.</p> Signup and view all the answers

    After an action potential fires, what is the state of the original active region?

    <p>It repolarizes back to resting membrane potential.</p> Signup and view all the answers

    What does the internal environment of the nerve axon become during depolarization?

    <p>Positive, relative to the outside.</p> Signup and view all the answers

    What is the role of adjacent inactive regions during action potential propagation?

    <p>They transition into active regions as depolarized.</p> Signup and view all the answers

    What characterizes the entire nerve axon at rest?

    <p>It is consistently at resting membrane potential.</p> Signup and view all the answers

    Which statement about the propagation of action potentials is inaccurate?

    <p>The entire axon depolarizes simultaneously at once.</p> Signup and view all the answers

    During the propagation of action potentials, what happens to the charges at the active site?

    <p>They flow to the adjacent inactive area, causing depolarization.</p> Signup and view all the answers

    What does the time constant (τ) indicate in the context of membrane potential?

    <p>The amount of time for the potential to change to 63% of its final value.</p> Signup and view all the answers

    Which factor increases the time constant (τ)?

    <p>Increasing membrane capacitance (Cₘ)</p> Signup and view all the answers

    What is the correct relationship expressed by the length constant (λ)?

    <p>λ ∝ √(Rₘ / Rᵢ)</p> Signup and view all the answers

    What effect does high membrane resistance (Rₘ) have on action potential conduction?

    <p>It increases the difficulty in changing the membrane potential.</p> Signup and view all the answers

    If a nerve fiber has a large diameter, what effect does this have on the length constant (λ)?

    <p>It increases the length constant.</p> Signup and view all the answers

    How does internal resistance (Rᵢ) influence conduction along a nerve fiber?

    <p>Lower internal resistance promotes faster conduction.</p> Signup and view all the answers

    What happens to the time constant (τ) when both membrane resistance (Rₘ) and membrane capacitance (Cₘ) are high?

    <p>The time constant is greatest.</p> Signup and view all the answers

    What is implied by a longer length constant (λ) in a nerve fiber?

    <p>Depolarizing current spreads farther down the nerve fiber.</p> Signup and view all the answers

    What role does membrane capacitance (Cₘ) play in the action potential propagation?

    <p>It influences the time taken for the membrane to become depolarized.</p> Signup and view all the answers

    Current flows along the path of least resistance in a nerve fiber. This relates to which concept?

    <p>Length constant</p> Signup and view all the answers

    Study Notes

    Refractory Periods

    • Excitable cells cannot produce normal action potentials during refractory periods (see Figure 1.13).
    • The refractory period includes absolute and relative refractory periods.

    Absolute Refractory Period

    • Overlaps with the entire action potential duration.
    • No action potential can be elicited, regardless of stimulus strength.
    • Caused by the inactivation gates of sodium (Na⁺) channels closing in response to depolarization.
    • Channels remain closed until the cell repolarizes to its resting membrane potential and become available again (see Figure 1.14).

    Relative Refractory Period

    • Begins after the absolute refractory period and overlaps with the hyperpolarizing afterpotential.
    • An action potential can be elicited, but requires a greater than usual depolarizing current.
    • Higher potassium (K⁺) conductance than at rest.
    • Membrane potential is closer to the K⁺ equilibrium potential, requiring more inward current to reach threshold.

    Accommodation

    • Slow depolarization or maintained depolarization levels can prevent action potential firing (accommodation).
    • Inactivation gates of sodium (Na⁺) channels close during slow depolarization.
    • Insufficient available Na⁺ channels to carry the required inward current for action potential upstroke.
    • An example is hyperkalemia (elevated serum K⁺ concentration). Increased extracellular K⁺ causes depolarization, bringing the membrane closer to threshold but actually decreasing the likelihood of firing due to the closed Na⁺ inactivation gates.

    Propagation of Action Potentials

    • Action potentials propagate along nerve/muscle fibers via local current flow from active regions to adjacent inactive regions.
    • Figure 1.15 illustrates this.
    • Positive charges inside the active region flow toward negative charges in the inactive region, depolarizing the adjacent region to threshold, triggering another action potential.
    • This process continues sequentially down the axon, transmitting the action potential.

    Conduction Velocity

    • The speed at which action potentials propagate down a nerve/muscle fiber.
    • Physiological importance in the nervous system.
    • Factors influencing conduction velocity:
      • Nerve fiber diameter: Larger fibers have lower internal resistance, allowing current flow farther, thus increasing the length constant and velocity.
      • Myelination: Myelin sheath increases membrane resistance, decreasing membrane capacitance, speeding up depolarization and conduction velocity. Action potentials "jump" between Nodes of Ranvier.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Action Potential PDF

    Description

    This quiz covers the concepts of refractory periods in excitable cells, including definitions and characteristics of absolute and relative refractory periods. It explores how these periods affect the generation of action potentials and the role of sodium and potassium channels in this process. Test your understanding of these critical concepts in neurophysiology.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser