Podcast
Questions and Answers
What is the primary cause of depolarization during an action potential?
What is the primary cause of depolarization during an action potential?
At what membrane potential level does the firing level occur during action potential?
At what membrane potential level does the firing level occur during action potential?
What characterizes the action potential's propagation?
What characterizes the action potential's propagation?
Which channels open as a direct result of membrane depolarization reaching -55 mV?
Which channels open as a direct result of membrane depolarization reaching -55 mV?
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What occurs during the repolarization phase of an action potential?
What occurs during the repolarization phase of an action potential?
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What is the effect of the negative feedback mechanism in the context of action potential?
What is the effect of the negative feedback mechanism in the context of action potential?
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What defines the all-or-nothing principle in action potentials?
What defines the all-or-nothing principle in action potentials?
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What change occurs in membrane potential during the rapid influx of Na+ ions?
What change occurs in membrane potential during the rapid influx of Na+ ions?
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What is the resting membrane potential (RMP) for nerve fibers?
What is the resting membrane potential (RMP) for nerve fibers?
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What occurs when the depolarization wave reaches the first electrode?
What occurs when the depolarization wave reaches the first electrode?
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Which of the following describes the duration of an action potential in muscle fibers?
Which of the following describes the duration of an action potential in muscle fibers?
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What is the magnitude of the spike potential in nerve fibers?
What is the magnitude of the spike potential in nerve fibers?
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Which condition is characterized by decreased serum potassium and recurrent muscle weakness?
Which condition is characterized by decreased serum potassium and recurrent muscle weakness?
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What happens to the potential difference when the depolarization wave returns to the baseline?
What happens to the potential difference when the depolarization wave returns to the baseline?
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What is the firing level for muscle fiber action potential?
What is the firing level for muscle fiber action potential?
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What characterizes the duration of after potentials in nerve fibers compared to muscle fibers?
What characterizes the duration of after potentials in nerve fibers compared to muscle fibers?
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What causes the closure of voltage-activated Na+ channels during the repolarization phase?
What causes the closure of voltage-activated Na+ channels during the repolarization phase?
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At what potential do voltage-activated K+ channels begin to open?
At what potential do voltage-activated K+ channels begin to open?
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What is the primary movement of ions during the repolarization phase?
What is the primary movement of ions during the repolarization phase?
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Which gate is responsible for the activation of voltage-gated Na+ channels?
Which gate is responsible for the activation of voltage-gated Na+ channels?
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What is hyperpolarization associated with during the action potential process?
What is hyperpolarization associated with during the action potential process?
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What role does the Na-K pump play in the action potential process?
What role does the Na-K pump play in the action potential process?
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Which of the following is NOT a part of the monophasic action potential record?
Which of the following is NOT a part of the monophasic action potential record?
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What equipment is used to record the action potential?
What equipment is used to record the action potential?
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What does the latent period of an action potential represent?
What does the latent period of an action potential represent?
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What triggers the rapid depolarization phase of the spike potential?
What triggers the rapid depolarization phase of the spike potential?
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Which phase is primarily responsible for repolarization during the action potential?
Which phase is primarily responsible for repolarization during the action potential?
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What is the characteristic membrane potential during the peak of the action potential?
What is the characteristic membrane potential during the peak of the action potential?
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Which type of after potential involves hyperpolarization of the membrane?
Which type of after potential involves hyperpolarization of the membrane?
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What primarily influences the duration of the latent period?
What primarily influences the duration of the latent period?
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Which component of the action potential occurs first in terms of ion movement?
Which component of the action potential occurs first in terms of ion movement?
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How long does the spike potential typically last in thick myelinated nerve fibers?
How long does the spike potential typically last in thick myelinated nerve fibers?
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What initiates the process of depolarization during action potential?
What initiates the process of depolarization during action potential?
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What occurs immediately after the membrane potential reaches -55 mV?
What occurs immediately after the membrane potential reaches -55 mV?
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During the repolarization phase of an action potential, which ion primarily moves out of the cell?
During the repolarization phase of an action potential, which ion primarily moves out of the cell?
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What is the range of membrane potential during the overshoot phase of an action potential?
What is the range of membrane potential during the overshoot phase of an action potential?
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What type of feedback mechanism is involved in the opening of Na+ channels during depolarization?
What type of feedback mechanism is involved in the opening of Na+ channels during depolarization?
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What is the final result of Na+ influx during the action potential?
What is the final result of Na+ influx during the action potential?
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What change occurs to the membrane potential due to electrotonic potentials before reaching the firing level?
What change occurs to the membrane potential due to electrotonic potentials before reaching the firing level?
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What is indicated by the term 'non-decremental' in relation to action potential propagation?
What is indicated by the term 'non-decremental' in relation to action potential propagation?
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What initiates the closure of voltage-activated Na+ channels during action potential repolarization?
What initiates the closure of voltage-activated Na+ channels during action potential repolarization?
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What is the result of the delayed opening of voltage-activated K+ channels during the action potential?
What is the result of the delayed opening of voltage-activated K+ channels during the action potential?
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What potential corresponds to the threshold for activating voltage-activated K+ channels?
What potential corresponds to the threshold for activating voltage-activated K+ channels?
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What phase follows the spike potential in a monophasic action potential recording?
What phase follows the spike potential in a monophasic action potential recording?
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During hyperpolarization, what is primarily responsible for the continuation of K+ ion diffusion outside the cell?
During hyperpolarization, what is primarily responsible for the continuation of K+ ion diffusion outside the cell?
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What essential function does the Na-K pump perform during the action potential?
What essential function does the Na-K pump perform during the action potential?
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What is the significance of using a cathode ray oscilloscope (CRO) in recording action potentials?
What is the significance of using a cathode ray oscilloscope (CRO) in recording action potentials?
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What characterizes the after potential phase in relation to the action potential?
What characterizes the after potential phase in relation to the action potential?
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Which factor does NOT affect the duration of the latent period in an action potential?
Which factor does NOT affect the duration of the latent period in an action potential?
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What characterizes the negative after potential in terms of membrane state?
What characterizes the negative after potential in terms of membrane state?
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Which phase primarily represents the rapid change in membrane potential during action potential?
Which phase primarily represents the rapid change in membrane potential during action potential?
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During the descending limb of the action potential, what primarily causes the repolarization of the membrane?
During the descending limb of the action potential, what primarily causes the repolarization of the membrane?
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What is the duration of the spike potential in thick myelinated nerve fibers?
What is the duration of the spike potential in thick myelinated nerve fibers?
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Which of the following represents the key event that marks the threshold potential during action potential?
Which of the following represents the key event that marks the threshold potential during action potential?
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The large wave of action potential is most accurately described by which potential change?
The large wave of action potential is most accurately described by which potential change?
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What physiological role does the phase of slow depolarization play in an action potential?
What physiological role does the phase of slow depolarization play in an action potential?
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How does the resting membrane potential (RMP) of nerve fibers compare to that of muscle fibers?
How does the resting membrane potential (RMP) of nerve fibers compare to that of muscle fibers?
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What is the impact of decreased serum potassium in the context of primary hypokalemic periodic paralysis?
What is the impact of decreased serum potassium in the context of primary hypokalemic periodic paralysis?
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What distinguishes the duration of action potentials between nerve fibers and muscle fibers?
What distinguishes the duration of action potentials between nerve fibers and muscle fibers?
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During the depolarization wave, what happens when the wave reaches the second electrode?
During the depolarization wave, what happens when the wave reaches the second electrode?
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Which characteristic of action potentials in muscle fibers differs from those in nerve fibers?
Which characteristic of action potentials in muscle fibers differs from those in nerve fibers?
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What occurs after the depolarization wave leaves the second electrode?
What occurs after the depolarization wave leaves the second electrode?
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Which feature is unique to the conduction of action potentials in nerve fibers compared to muscle fibers?
Which feature is unique to the conduction of action potentials in nerve fibers compared to muscle fibers?
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Which statement accurately reflects the characteristics of the after potentials in muscle fibers?
Which statement accurately reflects the characteristics of the after potentials in muscle fibers?
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What factors influence the duration of the latent period in an action potential?
What factors influence the duration of the latent period in an action potential?
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Describe the two phases of Na+ influx during the spike potential.
Describe the two phases of Na+ influx during the spike potential.
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How does repolarization occur after action potential?
How does repolarization occur after action potential?
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What is the significance of after potentials in the action potential process?
What is the significance of after potentials in the action potential process?
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Explain the confusion between depolarization and overshoot during the action potential.
Explain the confusion between depolarization and overshoot during the action potential.
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What is the role of the K+ efflux during the action potential?
What is the role of the K+ efflux during the action potential?
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What determines the membrane potential during the peak of the spike potential?
What determines the membrane potential during the peak of the spike potential?
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Discuss the implications of the overshoot phase in action potentials.
Discuss the implications of the overshoot phase in action potentials.
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Describe the change in membrane potential from resting membrane potential to overshoot during an action potential.
Describe the change in membrane potential from resting membrane potential to overshoot during an action potential.
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Explain how the positive feedback mechanism functions during the action potential.
Explain how the positive feedback mechanism functions during the action potential.
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What happens to the membrane potential at -63 mV, and why is it significant for action potential initiation?
What happens to the membrane potential at -63 mV, and why is it significant for action potential initiation?
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Identify the primary ion responsible for the repolarization phase of the action potential and its movement.
Identify the primary ion responsible for the repolarization phase of the action potential and its movement.
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What role do voltage-gated K+ channels play immediately after the peak of the action potential?
What role do voltage-gated K+ channels play immediately after the peak of the action potential?
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How does the all-or-nothing principle apply to action potentials?
How does the all-or-nothing principle apply to action potentials?
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Discuss the significance of the isoelectric line in relation to action potential changes.
Discuss the significance of the isoelectric line in relation to action potential changes.
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Explain what electrotonic potentials contribute to the action potential process.
Explain what electrotonic potentials contribute to the action potential process.
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Describe the role of the h gate during repolarization of the action potential.
Describe the role of the h gate during repolarization of the action potential.
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Explain the effect of voltage-activated K+ channels opening at threshold potential.
Explain the effect of voltage-activated K+ channels opening at threshold potential.
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What is the significance of the Na-K pump in relation to action potential recovery?
What is the significance of the Na-K pump in relation to action potential recovery?
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How does hyperpolarization occur after the repolarization phase of an action potential?
How does hyperpolarization occur after the repolarization phase of an action potential?
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What are the components recorded during a monophasic action potential?
What are the components recorded during a monophasic action potential?
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Describe the sequence of events occurring during the spike potential of an action potential.
Describe the sequence of events occurring during the spike potential of an action potential.
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Describe the difference in resting membrane potential (RMP) between nerve fibers and muscle fibers.
Describe the difference in resting membrane potential (RMP) between nerve fibers and muscle fibers.
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What is the physiological importance of the latent period in action potentials?
What is the physiological importance of the latent period in action potentials?
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How do K+ ion movements relate to the overall action potential process?
How do K+ ion movements relate to the overall action potential process?
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What is the magnitude of the spike potential for muscle fibers and how does it compare to that of nerve fibers?
What is the magnitude of the spike potential for muscle fibers and how does it compare to that of nerve fibers?
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Explain the significance of the isoelectric line in the biphasic action potential recording.
Explain the significance of the isoelectric line in the biphasic action potential recording.
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How does the duration of action potentials differ between nerve and muscle fibers?
How does the duration of action potentials differ between nerve and muscle fibers?
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What factors can trigger primary hypokalemic periodic paralysis?
What factors can trigger primary hypokalemic periodic paralysis?
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What occurs during the return to baseline potential after depolarization wave reaches the second electrode?
What occurs during the return to baseline potential after depolarization wave reaches the second electrode?
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Compare the conduction velocity of action potentials in nerve fibers and muscle fibers.
Compare the conduction velocity of action potentials in nerve fibers and muscle fibers.
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What is the characteristic change in membrane potential during the depolarization wave in nerve fibers?
What is the characteristic change in membrane potential during the depolarization wave in nerve fibers?
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Explain the role of Na+ influx during the depolarization phase of an action potential.
Explain the role of Na+ influx during the depolarization phase of an action potential.
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What is the significance of the firing level at -55 mV in the context of action potentials?
What is the significance of the firing level at -55 mV in the context of action potentials?
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Describe how the action potential is propagated along the nerve fiber.
Describe how the action potential is propagated along the nerve fiber.
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What occurs to the membrane potential during the overshoot phase of the action potential?
What occurs to the membrane potential during the overshoot phase of the action potential?
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How does voltage-gated K+ channel activity contribute to the repolarization phase?
How does voltage-gated K+ channel activity contribute to the repolarization phase?
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What role does the negative feedback mechanism play in the action potential?
What role does the negative feedback mechanism play in the action potential?
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In what way does the all-or-nothing principle apply to action potentials?
In what way does the all-or-nothing principle apply to action potentials?
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Define the term 'electrotonic potentials' and explain their relevance in the context of action potentials.
Define the term 'electrotonic potentials' and explain their relevance in the context of action potentials.
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What impact does the distance between stimulus and nerve fiber have on the latent period?
What impact does the distance between stimulus and nerve fiber have on the latent period?
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What occurs during the descending limb of the action potential?
What occurs during the descending limb of the action potential?
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How do after potentials reflect changes in membrane potential?
How do after potentials reflect changes in membrane potential?
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What is the significance of the threshold potential in action potentials?
What is the significance of the threshold potential in action potentials?
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Explain the difference between negative and positive after potentials.
Explain the difference between negative and positive after potentials.
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What are the two gates of voltage-gated Na+ channels, and what is their role during action potential?
What are the two gates of voltage-gated Na+ channels, and what is their role during action potential?
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Describe the mechanism of repolarization during an action potential.
Describe the mechanism of repolarization during an action potential.
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What triggers the rapid depolarization phase in action potentials?
What triggers the rapid depolarization phase in action potentials?
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How does the velocity of nerve fibers influence action potential?
How does the velocity of nerve fibers influence action potential?
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What happens to the membrane potential when voltage-gated K+ channels open during repolarization?
What happens to the membrane potential when voltage-gated K+ channels open during repolarization?
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At what potential do voltage-activated K+ channels begin to open, and what is the significance of this threshold?
At what potential do voltage-activated K+ channels begin to open, and what is the significance of this threshold?
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What is the consequence of the delayed closure of K+ channels during the repolarization phase?
What is the consequence of the delayed closure of K+ channels during the repolarization phase?
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Explain the role of the Na-K pump after an action potential occurs.
Explain the role of the Na-K pump after an action potential occurs.
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Outline the primary elements recorded in a monophasic action potential.
Outline the primary elements recorded in a monophasic action potential.
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What is the significance of using two microelectrodes in recording action potentials?
What is the significance of using two microelectrodes in recording action potentials?
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What is the primary difference in resting membrane potential (RMP) between nerve fibers and muscle fibers?
What is the primary difference in resting membrane potential (RMP) between nerve fibers and muscle fibers?
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Describe the duration of action potentials in nerve fibers compared to muscle fibers.
Describe the duration of action potentials in nerve fibers compared to muscle fibers.
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What triggers primary hypokalemic periodic paralysis?
What triggers primary hypokalemic periodic paralysis?
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Explain what happens at the second electrode during the action potential.
Explain what happens at the second electrode during the action potential.
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How does the conduction velocity of action potentials differ in nerve and muscle fibers?
How does the conduction velocity of action potentials differ in nerve and muscle fibers?
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What is the duration of after potentials in nerve fibers compared to muscle fibers?
What is the duration of after potentials in nerve fibers compared to muscle fibers?
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At what membrane potential does the firing level occur for nerve fibers?
At what membrane potential does the firing level occur for nerve fibers?
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Study Notes
Action Potential
- Action potential is a rapid electrical change in nerve fibers due to effective stimulus
- It's actively propagated, non-decremental, and obeys the all-or-none rule
- Action potential phases include depolarization and repolarization
Depolarization
- Caused by sodium (Na⁺) influx
- Involves voltage-gated Na⁺ channels
- Adds negative charges to the outer membrane surface
- Passive depolarization occurs when the membrane potential changes by about 7mV
- Some voltage-gated Na⁺ channels open allowing Na⁺ influx
- Leads to the opening of more voltage-activated Na⁺ channels, increasing Na⁺ influx
- Further decreases the membrane potential through positive feedback
- Membrane potential reaches the firing level (–55 mV), initiating active depolarization
- All voltage-gated Na⁺ channels open, causing rapid Na⁺ influx
- The membrane potential rapidly rises to zero and overshoots to approximately +35mV, reversing polarity
Repolarization
- Restoration of the membrane potential to its resting value
- Sodium (Na⁺) influx stops due to the closure of voltage-gated Na⁺ channels' h-gate
- Voltage-gated K⁺ channels open, allowing potassium (K⁺) influx
- K⁺ ions continue to diffuse outwards, leading to hyperpolarization
- This returns the inside of the membrane to its original negative potential (-70mV)
Ionic Basis of Action Potential
- Depolarization: Loss of normal polarized state, due to stimulus increasing membrane permeability to sodium ions (Na⁺), causing them to diffuse into the cell, changing membrane potential
- Steps: Stimulus (cathode) adds negative charges to the outer membrane surface, changes the membrane potential by about 7 mV (from -70 mV to 63 mV), some voltage-gated Na⁺ channels open allowing Na⁺ influx, membrane potential increases, leading to the opening of more voltage-activated Na⁺ channels, causing a positive feedback mechanism
- Membrane potential reaches to -55mV, triggering active depolarization. All voltage-gated Na⁺ are open, leading to rapid Na⁺ influx, reaching zero potential and overshooting by +35mV
Recording of Action Potential
- Apparatus: Cathode ray oscilloscope (CRO)
-
Methods: Monophasic
- Two microelectrodes are used: one for recording inside the nerve fibers, the other as a reference outside
- The initial positive wave followed by a negative wave, separated by an isoelectric line, are recorded
- Latent period, spike potential, and after-potential phases are identified
A. Latent Period
- Time between the nerve stimulation and the start of the action potential
- Represents time taken by an impulse to travel from the stimulation site to the recording electrodes
- Affected by distance between the stimulus and the nerve fiber and the velocity of the nerve fibers
B. Spike Potential
- A large wave, measuring 105 mV from -70 to +35 mV
- Short duration, ranging from 0.5 to 1 msec in myelinated nerve fibers
- Consists of two phases:
- Slow depolarization: gradual Na⁺ influx causing slow changes in membrane potential (-70 mV → -55 mV)
- Rapid depolarization (upstroke): Voltage-sensitive Na⁺ channels open, rapid Na⁺ influx, and rapid depolarization of the membrane, reaching positive values until it reverses polarity (+35mV)
C. After Potentials
- Small waves with relatively longer durations
- Types:
- Negative after-potential: short duration (4 msec), membrane is partially depolarized, due to slow K⁺ efflux
- Positive after-potential: long duration (40 msec), membrane is hyperpolarized, due to continued K⁺ efflux caused by slow closure of K⁺ channels
Action Potential in Skeletal Muscles
- RMP (-90 mV): Resting membrane potential in skeletal muscle cells
- Firing level (-50 mV): Threshold potential in skeletal muscle for initiating an action potential
- Magnitude of the Spike potential(130 mV)
- Duration of the AP (3-5 msec)
- Duration of After potential (Long)
- Velocity of conduction of the AP (3-5 m/sec)
Clinical Correlation
- Primary Hypokalemic Periodic Paralysis:
- Inherited disorder characterized by decreased serum potassium (K⁺)
- Recurrent attacks of muscle weakness, sometimes paralysis
- Triggered by exercise and worsened by carbohydrate consumption
Action Potential in Nerve Fibers
- RMP (-70 mV): Resting membrane potential in nerve cells
- Firing level (-55 mV): Threshold potential in nerve cells for triggering an action potential
- Magnitude of the Spike potential(105 mV)
- Duration of the AP (0.5-1 msec)
- Duration of After potential (Short)
- Velocity of conduction of the AP (up to 120 m/sec)
Biphasic Action Potential
- Two microelectrodes are used to record the action potential, one for measuring and the other for reference
- Initial positive wave followed by a negative wave, separated by an isoelectric line
- Depolarization causes an upward deflection when the wave reaches the recording electrode, and a return to zero potential when it leaves
- The wave moving to the next electrodes will produce changes, showing downward deflection and return to zero
Na-K Pump
- Active transport that moves sodium (Na⁺) ions out and potassium (K⁺) ions into the cell, crucial for restoring ion concentrations after an action potential
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