أسئلة المحاضرة الـ 14 فسيولوجي (قبل التعديل)
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Questions and Answers

What is the primary cause of depolarization during an action potential?

  • K+ efflux
  • Ca2+ efflux
  • Na+ influx (correct)
  • Cl- influx

    • At what membrane potential level does the firing level occur during action potential?

  • +35 mV
  • -55 mV (correct)
  • -70 mV
  • 0 mV

    • What characterizes the action potential's propagation?

  • It is decremental.
  • It is actively propagated. (correct)
  • It is passive only.
  • It is always overshooting.

    • Which channels open as a direct result of membrane depolarization reaching -55 mV?

    <p>Voltage-gated Na+ channels (A)</p> Signup and view all the answers

    What occurs during the repolarization phase of an action potential?

    <p>K+ ions exit the cell (A)</p> Signup and view all the answers

    What is the effect of the negative feedback mechanism in the context of action potential?

    <p>It enhances Na+ channel opening. (A)</p> Signup and view all the answers

    What defines the all-or-nothing principle in action potentials?

    <p>Action potentials do not occur at all until the threshold is reached. (D)</p> Signup and view all the answers

    What change occurs in membrane potential during the rapid influx of Na+ ions?

    <p>It progressively reaches zero. (B)</p> Signup and view all the answers

    What is the resting membrane potential (RMP) for nerve fibers?

    <p>-70 mV (A)</p> Signup and view all the answers

    What occurs when the depolarization wave reaches the first electrode?

    <p>Upward deflection is recorded (A)</p> Signup and view all the answers

    Which of the following describes the duration of an action potential in muscle fibers?

    <p>3-5 msec (B)</p> Signup and view all the answers

    What is the magnitude of the spike potential in nerve fibers?

    <p>105 mV (D)</p> Signup and view all the answers

    Which condition is characterized by decreased serum potassium and recurrent muscle weakness?

    <p>Hypokalemic periodic paralysis (B)</p> Signup and view all the answers

    What happens to the potential difference when the depolarization wave returns to the baseline?

    <p>Potential difference returns to zero (D)</p> Signup and view all the answers

    What is the firing level for muscle fiber action potential?

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

    What characterizes the duration of after potentials in nerve fibers compared to muscle fibers?

    <p>Nerve fibers have shorter after potentials (B)</p> Signup and view all the answers

    What causes the closure of voltage-activated Na+ channels during the repolarization phase?

    <p>Activation of inactivation gate (h gate) (D)</p> Signup and view all the answers

    At what potential do voltage-activated K+ channels begin to open?

    <p>Threshold potential (-55 mV) (D)</p> Signup and view all the answers

    What is the primary movement of ions during the repolarization phase?

    <p>K+ ions diffuse outside the cell (C)</p> Signup and view all the answers

    Which gate is responsible for the activation of voltage-gated Na+ channels?

    <p>Activation gate (m gate) (B)</p> Signup and view all the answers

    What is hyperpolarization associated with during the action potential process?

    <p>Excessive efflux of K+ ions (B)</p> Signup and view all the answers

    What role does the Na-K pump play in the action potential process?

    <p>It restores resting membrane potential (D)</p> Signup and view all the answers

    Which of the following is NOT a part of the monophasic action potential record?

    <p>During potential (D)</p> Signup and view all the answers

    What equipment is used to record the action potential?

    <p>Cathode ray oscilloscope (CRO) (C)</p> Signup and view all the answers

    What does the latent period of an action potential represent?

    <p>Time taken for impulse to travel to recording electrodes. (B)</p> Signup and view all the answers

    What triggers the rapid depolarization phase of the spike potential?

    <p>Sudden influx of Na+ ions. (D)</p> Signup and view all the answers

    Which phase is primarily responsible for repolarization during the action potential?

    <p>K+ efflux through opened channels. (A)</p> Signup and view all the answers

    What is the characteristic membrane potential during the peak of the action potential?

    <p>+35 mV (A)</p> Signup and view all the answers

    Which type of after potential involves hyperpolarization of the membrane?

    <p>Positive after potential (B)</p> Signup and view all the answers

    What primarily influences the duration of the latent period?

    <p>Distance between stimulus and nerve fiber. (B)</p> Signup and view all the answers

    Which component of the action potential occurs first in terms of ion movement?

    <p>Na+ influx (A)</p> Signup and view all the answers

    How long does the spike potential typically last in thick myelinated nerve fibers?

    <p>0.5–1 msec (C)</p> Signup and view all the answers

    What initiates the process of depolarization during action potential?

    <p>An effective stimulus enhancing Na+ permeability (A)</p> Signup and view all the answers

    What occurs immediately after the membrane potential reaches -55 mV?

    <p>Voltage-gated Na+ channels open and Na+ influx occurs (D)</p> Signup and view all the answers

    During the repolarization phase of an action potential, which ion primarily moves out of the cell?

    <p>K+ ions (A)</p> Signup and view all the answers

    What is the range of membrane potential during the overshoot phase of an action potential?

    <p>0 mV to +35 mV (C)</p> Signup and view all the answers

    What type of feedback mechanism is involved in the opening of Na+ channels during depolarization?

    <p>Positive feedback (D)</p> Signup and view all the answers

    What is the final result of Na+ influx during the action potential?

    <p>Achieving peak membrane potential at approximately +35 mV (B)</p> Signup and view all the answers

    What change occurs to the membrane potential due to electrotonic potentials before reaching the firing level?

    <p>It decreases to -63 mV (A)</p> Signup and view all the answers

    What is indicated by the term 'non-decremental' in relation to action potential propagation?

    <p>The action potential travels without loss of strength (A)</p> Signup and view all the answers

    What initiates the closure of voltage-activated Na+ channels during action potential repolarization?

    <p>Activation of h gate (D)</p> Signup and view all the answers

    What is the result of the delayed opening of voltage-activated K+ channels during the action potential?

    <p>Diffusion of K+ ions outside the cell (C)</p> Signup and view all the answers

    What potential corresponds to the threshold for activating voltage-activated K+ channels?

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

    What phase follows the spike potential in a monophasic action potential recording?

    <p>After potential phase (A)</p> Signup and view all the answers

    During hyperpolarization, what is primarily responsible for the continuation of K+ ion diffusion outside the cell?

    <p>Delayed closure of K+ channels (B)</p> Signup and view all the answers

    What essential function does the Na-K pump perform during the action potential?

    <p>Restores ion balance after action potential (A)</p> Signup and view all the answers

    What is the significance of using a cathode ray oscilloscope (CRO) in recording action potentials?

    <p>To observe real-time changes in membrane potential (D)</p> Signup and view all the answers

    What characterizes the after potential phase in relation to the action potential?

    <p>May involve hyperpolarization patterns (C)</p> Signup and view all the answers

    Which factor does NOT affect the duration of the latent period in an action potential?

    <p>Magnitude of spike potential (B)</p> Signup and view all the answers

    What characterizes the negative after potential in terms of membrane state?

    <p>It involves a hyperpolarized membrane (D)</p> Signup and view all the answers

    Which phase primarily represents the rapid change in membrane potential during action potential?

    <p>Rapid depolarization (A)</p> Signup and view all the answers

    During the descending limb of the action potential, what primarily causes the repolarization of the membrane?

    <p>K+ ions rapidly effluxing (D)</p> Signup and view all the answers

    What is the duration of the spike potential in thick myelinated nerve fibers?

    <p>1 msec (B)</p> Signup and view all the answers

    Which of the following represents the key event that marks the threshold potential during action potential?

    <p>Membrane potential reaches -55 mV (B)</p> Signup and view all the answers

    The large wave of action potential is most accurately described by which potential change?

    <p>A shift from -70 mV to +35 mV (B)</p> Signup and view all the answers

    What physiological role does the phase of slow depolarization play in an action potential?

    <p>Gradually increases membrane potential to a threshold (C)</p> Signup and view all the answers

    How does the resting membrane potential (RMP) of nerve fibers compare to that of muscle fibers?

    <p>RMP of nerve fibers is lower than that of muscle fibers. (C)</p> Signup and view all the answers

    What is the impact of decreased serum potassium in the context of primary hypokalemic periodic paralysis?

    <p>It causes recurrent muscle weakness and sometimes paralysis. (C)</p> Signup and view all the answers

    What distinguishes the duration of action potentials between nerve fibers and muscle fibers?

    <p>Action potentials in muscle fibers are significantly longer than in nerve fibers. (C)</p> Signup and view all the answers

    During the depolarization wave, what happens when the wave reaches the second electrode?

    <p>A downward deflection is recorded. (D)</p> Signup and view all the answers

    Which characteristic of action potentials in muscle fibers differs from those in nerve fibers?

    <p>Muscle fibers have a longer magnitude of spike potential. (C)</p> Signup and view all the answers

    What occurs after the depolarization wave leaves the second electrode?

    <p>The potential difference returns again to zero. (B)</p> Signup and view all the answers

    Which feature is unique to the conduction of action potentials in nerve fibers compared to muscle fibers?

    <p>Nerve fibers can exceed a conduction velocity of 120 m/sec. (B)</p> Signup and view all the answers

    Which statement accurately reflects the characteristics of the after potentials in muscle fibers?

    <p>After potentials are typically longer in nerve fibers. (D)</p> Signup and view all the answers

    What factors influence the duration of the latent period in an action potential?

    <p>The distance between the stimulus and nerve fiber, and the velocity of the nerve fibers.</p> Signup and view all the answers

    Describe the two phases of Na+ influx during the spike potential.

    <p>The slow depolarization involves gradual Na+ influx to reach the threshold, followed by rapid depolarization as voltage-sensitive Na+ channels open, resulting in a sudden influx.</p> Signup and view all the answers

    How does repolarization occur after action potential?

    <p>Repolarization occurs due to the sudden opening of voltage-sensitive K+ channels, leading to rapid K+ efflux.</p> Signup and view all the answers

    What is the significance of after potentials in the action potential process?

    <p>After potentials represent brief fluctuations in membrane potential that occur following the spike potential, indicating the dynamics of ion flow post-depolarization.</p> Signup and view all the answers

    Explain the confusion between depolarization and overshoot during the action potential.

    <p>Depolarization refers to the membrane potential changing from -70 mV to +35 mV, while overshoot is the moment when the potential exceeds 0 mV during this rapid change.</p> Signup and view all the answers

    What is the role of the K+ efflux during the action potential?

    <p>K+ efflux is crucial for repolarizing the membrane, bringing it back to its resting potential after the spike.</p> Signup and view all the answers

    What determines the membrane potential during the peak of the spike potential?

    <p>The peak of the spike potential occurs around +35 mV and is determined by the rapid influx of Na+ ions.</p> Signup and view all the answers

    Discuss the implications of the overshoot phase in action potentials.

    <p>The overshoot phase indicates a complete reversal of the resting membrane potential, which is critical for signaling and ensuring the non-decremental nature of action potentials.</p> Signup and view all the answers

    Describe the change in membrane potential from resting membrane potential to overshoot during an action potential.

    <p>The membrane potential changes from $-70$ mV at resting state to approximately $+35$ mV during overshoot.</p> Signup and view all the answers

    Explain how the positive feedback mechanism functions during the action potential.

    <p>As sodium channels open, Na+ influx causes further depolarization, which opens even more sodium channels, amplifying the process.</p> Signup and view all the answers

    What happens to the membrane potential at -63 mV, and why is it significant for action potential initiation?

    <p>At -63 mV, the stimulus induces passive depolarization, leading to the opening of voltage-gated Na+ channels and reaching the firing level.</p> Signup and view all the answers

    Identify the primary ion responsible for the repolarization phase of the action potential and its movement.

    <p>The primary ion responsible for repolarization is K+, which moves out of the cell.</p> Signup and view all the answers

    What role do voltage-gated K+ channels play immediately after the peak of the action potential?

    <p>Voltage-gated K+ channels open, allowing K+ to exit, which promotes repolarization.</p> Signup and view all the answers

    How does the all-or-nothing principle apply to action potentials?

    <p>Action potentials either occur fully or not at all once the threshold is reached, rather than in varying degrees.</p> Signup and view all the answers

    Discuss the significance of the isoelectric line in relation to action potential changes.

    <p>The isoelectric line represents the point of zero potential, marking the transition from negative to positive during depolarization.</p> Signup and view all the answers

    Explain what electrotonic potentials contribute to the action potential process.

    <p>Electrotonic potentials contribute by initially reducing the potential difference, facilitating the depolarization process.</p> Signup and view all the answers

    Describe the role of the h gate during repolarization of the action potential.

    <p>The h gate closes to stop the influx of Na+ ions, contributing to the repolarization process.</p> Signup and view all the answers

    Explain the effect of voltage-activated K+ channels opening at threshold potential.

    <p>The opening of K+ channels allows K+ ions to diffuse out, leading to the inside of the membrane becoming more negative.</p> Signup and view all the answers

    What is the significance of the Na-K pump in relation to action potential recovery?

    <p>The Na-K pump actively transports Na+ out of and K+ into the cell, restoring the concentrations necessary for the next action potential.</p> Signup and view all the answers

    How does hyperpolarization occur after the repolarization phase of an action potential?

    <p>Hyperpolarization occurs due to the delayed closure of voltage-gated K+ channels, allowing excess K+ to exit the cell.</p> Signup and view all the answers

    What are the components recorded during a monophasic action potential?

    <p>The recorded components include the latent period, spike potential, and after potential.</p> Signup and view all the answers

    Describe the sequence of events occurring during the spike potential of an action potential.

    <p>During the spike potential, Na+ channels open rapidly, causing an influx of Na+ ions that sharply depolarizes the membrane.</p> Signup and view all the answers

    Describe the difference in resting membrane potential (RMP) between nerve fibers and muscle fibers.

    <p>-70 mV for nerve fibers and -90 mV for muscle fibers.</p> Signup and view all the answers

    What is the physiological importance of the latent period in action potentials?

    <p>The latent period represents the time it takes for depolarization to reach a sufficient level to activate action potential firing.</p> Signup and view all the answers

    How do K+ ion movements relate to the overall action potential process?

    <p>K+ ions primarily move out of the cell during repolarization, contributing to the return of the membrane potential to its resting state.</p> Signup and view all the answers

    What is the magnitude of the spike potential for muscle fibers and how does it compare to that of nerve fibers?

    <p>The spike potential for muscle fibers is 130 mV, while for nerve fibers it is 105 mV.</p> Signup and view all the answers

    Explain the significance of the isoelectric line in the biphasic action potential recording.

    <p>The isoelectric line indicates no potential difference between electrodes during rest and serves as a baseline for recordings.</p> Signup and view all the answers

    How does the duration of action potentials differ between nerve and muscle fibers?

    <p>Action potentials last 0.5-1 msec in nerve fibers and 3-5 msec in muscle fibers.</p> Signup and view all the answers

    What factors can trigger primary hypokalemic periodic paralysis?

    <p>It can be triggered by exercise and worsened by carbohydrate intake.</p> Signup and view all the answers

    What occurs during the return to baseline potential after depolarization wave reaches the second electrode?

    <p>The potential difference returns to zero.</p> Signup and view all the answers

    Compare the conduction velocity of action potentials in nerve fibers and muscle fibers.

    <p>Nerve fibers conduct action potentials at up to 120 m/sec, whereas muscle fibers conduct at 3-5 m/sec.</p> Signup and view all the answers

    What is the characteristic change in membrane potential during the depolarization wave in nerve fibers?

    <p>An upward deflection is recorded when the depolarization wave reaches the first electrode.</p> Signup and view all the answers

    Explain the role of Na+ influx during the depolarization phase of an action potential.

    <p>Na+ influx causes the membrane potential to become less negative, leading to rapid depolarization and a change in polarity.</p> Signup and view all the answers

    What is the significance of the firing level at -55 mV in the context of action potentials?

    <p>The firing level at -55 mV is the threshold at which rapid depolarization occurs, triggering the action potential.</p> Signup and view all the answers

    Describe how the action potential is propagated along the nerve fiber.

    <p>The action potential is actively propagated in a non-decremental manner, maintaining its amplitude as it travels.</p> Signup and view all the answers

    What occurs to the membrane potential during the overshoot phase of the action potential?

    <p>During the overshoot phase, the membrane potential rapidly rises to about +35 mV, indicating reversal of polarity.</p> Signup and view all the answers

    How does voltage-gated K+ channel activity contribute to the repolarization phase?

    <p>Voltage-gated K+ channels open, allowing K+ ions to exit the cell, which helps restore the membrane potential to its resting state.</p> Signup and view all the answers

    What role does the negative feedback mechanism play in the action potential?

    <p>The negative feedback mechanism helps stabilize the membrane potential by preventing excessive depolarization and ensuring proper repolarization.</p> Signup and view all the answers

    In what way does the all-or-nothing principle apply to action potentials?

    <p>The all-or-nothing principle dictates that once the membrane potential reaches the firing level, an action potential is initiated with full amplitude.</p> Signup and view all the answers

    Define the term 'electrotonic potentials' and explain their relevance in the context of action potentials.

    <p>Electrotonic potentials are local changes in membrane potential that result from stimulus-induced ion movement, contributing to passive depolarization.</p> Signup and view all the answers

    What impact does the distance between stimulus and nerve fiber have on the latent period?

    <p>A greater distance increases the latency due to longer travel time of the impulse.</p> Signup and view all the answers

    What occurs during the descending limb of the action potential?

    <p>Voltage-sensitive K channels open, leading to a rapid efflux of K+ and re-establishment of the resting membrane potential.</p> Signup and view all the answers

    How do after potentials reflect changes in membrane potential?

    <p>After potentials are small waves following the action potential, indicating partial depolarization or hyperpolarization of the membrane.</p> Signup and view all the answers

    What is the significance of the threshold potential in action potentials?

    <p>The threshold potential is crucial as it triggers the opening of Na+ channels, leading to rapid depolarization.</p> Signup and view all the answers

    Explain the difference between negative and positive after potentials.

    <p>Negative after potentials involve short-duration partial depolarization, while positive after potentials cause longer-duration hyperpolarization.</p> Signup and view all the answers

    What are the two gates of voltage-gated Na+ channels, and what is their role during action potential?

    <p>The two gates are the m gate (activation gate) and the h gate (inactivation gate). They control the influx of Na+ ions during depolarization and the closure of channels during repolarization.</p> Signup and view all the answers

    Describe the mechanism of repolarization during an action potential.

    <p>Repolarization occurs when voltage-gated Na+ channels close, halting Na+ influx, while voltage-gated K+ channels open, allowing K+ ions to diffuse out of the cell.</p> Signup and view all the answers

    What triggers the rapid depolarization phase in action potentials?

    <p>The rapid depolarization phase is triggered by voltage-sensitive Na channels opening at the firing level.</p> Signup and view all the answers

    How does the velocity of nerve fibers influence action potential?

    <p>Higher velocity in nerve fibers results in a shorter latent period, allowing for quicker signal transmission.</p> Signup and view all the answers

    What happens to the membrane potential when voltage-gated K+ channels open during repolarization?

    <p>The membrane potential becomes more negative as K+ ions diffuse out, leading to the restoration of the resting membrane potential.</p> Signup and view all the answers

    At what potential do voltage-activated K+ channels begin to open, and what is the significance of this threshold?

    <p>Voltage-activated K+ channels begin to open at -55 mV. This threshold is significant as it marks the onset of the repolarization phase of the action potential.</p> Signup and view all the answers

    What is the consequence of the delayed closure of K+ channels during the repolarization phase?

    <p>The delayed closure of K+ channels can result in hyperpolarization, where the membrane potential temporarily becomes more negative than the resting level.</p> Signup and view all the answers

    Explain the role of the Na-K pump after an action potential occurs.

    <p>The Na-K pump actively transports Na+ ions out of the cell and K+ ions into the cell, helping to restore and maintain the resting membrane potential.</p> Signup and view all the answers

    Outline the primary elements recorded in a monophasic action potential.

    <p>A monophasic action potential typically includes the latent period, spike potential, and after potential.</p> Signup and view all the answers

    What is the significance of using two microelectrodes in recording action potentials?

    <p>Using two microelectrodes allows for accurate recording, with one electrode measuring the potential inside the nerve fibers and the other serving as a reference outside.</p> Signup and view all the answers

    What is the primary difference in resting membrane potential (RMP) between nerve fibers and muscle fibers?

    <p>-70 mV for nerve fibers and -90 mV for muscle fibers.</p> Signup and view all the answers

    Describe the duration of action potentials in nerve fibers compared to muscle fibers.

    <p>Nerve fibers have action potentials lasting 0.5-1 msec, while muscle fibers last 3-5 msec.</p> Signup and view all the answers

    What triggers primary hypokalemic periodic paralysis?

    <p>It is triggered by decreased serum potassium and worsens with carbohydrate intake.</p> Signup and view all the answers

    Explain what happens at the second electrode during the action potential.

    <p>A downward deflection is recorded when the depolarization wave reaches the second electrode.</p> Signup and view all the answers

    How does the conduction velocity of action potentials differ in nerve and muscle fibers?

    <p>Nerve fibers can conduct action potentials up to 120 m/sec, while muscle fibers conduct at 3-5 m/sec.</p> Signup and view all the answers

    What is the duration of after potentials in nerve fibers compared to muscle fibers?

    <p>Nerve fibers have short after potentials, while muscle fibers have long after potentials.</p> Signup and view all the answers

    At what membrane potential does the firing level occur for nerve fibers?

    <p>The firing level for nerve fibers occurs at -55 mV.</p> Signup and view all the answers

    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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