أسئلة المحاضرة الـ 14 فسيولوجي (قبل التعديل)
126 Questions
0 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 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

Flashcards

Action Potential (AP)

A rapid electrical change in Resting Membrane Potential (RMP) of a nerve fiber, initiated by a stimulus.

Depolarization

A phase of the action potential where the membrane potential becomes less negative, due to sodium influx.

Repolarization

The phase of AP where the membrane potential returns to its resting state, mostly through potassium efflux.

Voltage-gated Na+ channels

Channels that open or close in response to changes in membrane potential, crucial for rapid sodium influx during depolarization.

Signup and view all the flashcards

Voltage-gated K+ channels

Channels that open or close in response to changes in membrane potential, crucial for repolarization by potassium efflux.

Signup and view all the flashcards

Firing Level

The critical membrane potential (-55mV) at which enough voltage-gated Na+ channels open to trigger a full action potential, resulting in depolarization.

Signup and view all the flashcards

Electrotonic Potential

A small, passive change in membrane potential spreading locally from the stimulus, acting as a step to the firing level.

Signup and view all the flashcards

Resting Membrane Potential (RMP)

The stable membrane potential of a neuron at rest, usually around -70mV, maintained by ion gradients.

Signup and view all the flashcards

Action Potential (AP) Restoration

Process of returning the membrane potential to its resting value after depolarization.

Signup and view all the flashcards

Na+ Channel Closure

Voltage-gated sodium channels close, stopping sodium influx during repolarization.

Signup and view all the flashcards

K+ Channel Opening

Voltage-gated potassium channels open, allowing potassium ions to flow out of the cell. This repolarizes the membrane.

Signup and view all the flashcards

Hyperpolarization

Temporary dip below the resting membrane potential due to prolonged K+ diffusion.

Signup and view all the flashcards

Na-K Pump

Actively transports sodium ions out of the cell and potassium ions into the cell to restore ion gradients.

Signup and view all the flashcards

Monophasic Action Potential

Action potential recorded using two microelectrodes, one inside the nerve fiber and one outside.

Signup and view all the flashcards

Components of AP record

includes latent period, spike potential, and after potential.

Signup and view all the flashcards

Latent Period (AP)

The time between nerve stimulation and the start of the action potential. This is the time taken for the impulse to travel from stimulation to recording.

Signup and view all the flashcards

Spike Potential (AP)

A large, rapid wave (from -70 to +35 mV) representing depolarization. It's caused by sodium influx, including two phases: slow depolarization and rapid depolarization.

Signup and view all the flashcards

Slow Depolarization (AP)

The gradual increase in membrane potential from rest towards the threshold potential due to sodium influx

Signup and view all the flashcards

Rapid Depolarization (AP)

A sudden increase in membrane potential, due to a rapid influx of sodium ions.

Signup and view all the flashcards

Repolarization (AP)

The process of returning the membrane potential to its resting state, primarily due to potassium efflux.

Signup and view all the flashcards

Negative Afterpotential (AP)

A short-duration, slight depolarizing wave following repolarization, resulting from slow potassium efflux.

Signup and view all the flashcards

Positive Afterpotential (AP)

A long-duration slight hyperpolarizing wave after repolarization, resulting from slow closing of potassium channels .

Signup and view all the flashcards

Velocity of nerve conduction

Speed at which nerve impulses travel along a nerve fiber, affected by factors like distance and fiber type.

Signup and view all the flashcards

Biphasic Action Potential

An action potential recorded using two microelectrodes on the surface of a nerve fiber, resulting in two waves: an initial positive wave followed by a negative wave.

Signup and view all the flashcards

How is 'Rest' recorded?

When there is no potential difference between the two electrodes, the recording will show a flat line, indicating the nerve fiber is at rest.

Signup and view all the flashcards

Depolarization Wave & 1st Electrode

When the depolarization wave reaches the first electrode, it causes an upward deflection in the recording.

Signup and view all the flashcards

Depolarization Wave & 2nd Electrode

When the depolarization wave passes the second electrode, it causes a downward deflection in the recording.

Signup and view all the flashcards

Action Potential in Nerve Fibers

The action potential in nerve fibers has a resting membrane potential of -70 mV, a firing level of -55 mV, a spike potential magnitude of 105 mV, a duration of 0.5-1 msec, and a conduction velocity of up to 120 m/sec.

Signup and view all the flashcards

Action Potential in Muscle Fibers

The action potential in muscle fibers has a resting membrane potential of -90 mV, a firing level of -50 mV, a spike potential magnitude of 130 mV, a duration of 3-5 msec, and a conduction velocity of 3-5 m/sec.

Signup and view all the flashcards

Primary Hypokalemic Periodic Paralysis

A genetic disorder marked by low potassium levels in the blood, causing recurrent episodes of muscle weakness and sometimes paralysis.

Signup and view all the flashcards

Triggers of Primary Hypokalemic Periodic Paralysis

This disorder is triggered by exercise and exacerbated by consuming carbohydrates.

Signup and view all the flashcards

What is the Action Potential (AP)?

It's a quick electrical burst within a nerve fiber, triggered by a stimulus. Unlike regular electrical signals, it travels without decreasing in strength and follows the 'all or nothing' principle.

Signup and view all the flashcards

How does Depolarization happen?

Sodium ions (Na+) rush into the nerve fiber, making the inside less negative, and eventually even positive. This change in charge is called depolarization.

Signup and view all the flashcards

What happens during Repolarization?

Potassium ions (K+) flow out of the nerve fiber, restoring the negative charge inside. This is repolarization.

Signup and view all the flashcards

What is the Firing Level?

It's the critical point where the membrane potential reaches -55mV, triggering a full action potential.

Signup and view all the flashcards

Explain Electrotonic Potentials

These are small, passive changes in membrane potential, spreading locally from the stimulus. They act as a step towards reaching the firing level.

Signup and view all the flashcards

What is the role of Voltage-gated Na+ Channels?

These channels open in response to changes in membrane potential, allowing sodium ions to flood in during depolarization.

Signup and view all the flashcards

What is the role of Voltage-gated K+ Channels?

They open during repolarization, allowing potassium ions to flow out, restoring the negative charge inside the nerve fiber.

Signup and view all the flashcards

Why does the AP obey 'all or nothing' rule?

Once the firing level is reached, a full action potential is triggered, irrespective of the stimulus' strength. It either happens fully or not at all.

Signup and view all the flashcards

Latent Period

The time between nerve stimulation and the start of the action potential. Represents the time taken for the impulse to travel from the stimulation point to the recording electrodes.

Signup and view all the flashcards

Spike Potential

The large wave (105 mV from -70 to +35 mV) during the action potential, representing depolarization. Caused by rapid sodium influx.

Signup and view all the flashcards

Ascending Limb

The part of the spike potential where the membrane potential rapidly increases, driven by sodium influx.

Signup and view all the flashcards

Descending Limb

The part of the spike potential where the membrane potential rapidly decreases, driven by potassium efflux.

Signup and view all the flashcards

Afterpotentials

Small waves following the spike potential representing further changes in the membrane potential. They are either negative or positive, depending on whether the membrane is partially depolarized or hyperpolarized.

Signup and view all the flashcards

Negative After Potential

Short duration wave after the spike potential, representing partial depolarization due to continuous K+ efflux.

Signup and view all the flashcards

Positive Afterpotential

Longer duration wave after the spike potential, representing hyperpolarization due to the slow closure of K+ channels.

Signup and view all the flashcards

Conduction Velocity

The speed at which a nerve impulse travels along a nerve fiber. Factors like distance and fiber type influence it.

Signup and view all the flashcards

What is a biphasic AP?

An action potential recorded using two electrodes placed on the surface of a nerve fiber. This results in two waves: an initial positive wave followed by a negative wave.

Signup and view all the flashcards

How is the first wave generated?

When the depolarization wave reaches the first electrode, it causes an upward deflection in the recording.

Signup and view all the flashcards

How is the second wave generated?

When the depolarization wave passes the second electrode, it causes a downward deflection in the recording.

Signup and view all the flashcards

What is Primary Hypokalemic Periodic Paralysis?

A genetic disorder characterized by low potassium levels in the blood, causing recurrent muscle weakness and sometimes paralysis.

Signup and view all the flashcards

What triggers the paralysis?

This disorder is triggered by exercise and exacerbated by consuming carbohydrates.

Signup and view all the flashcards

What is the difference between Nerve and Muscle AP?

Nerve APs are faster, shorter, and have a smaller magnitude than Muscle APs.

Signup and view all the flashcards

What are the 4 main phases of a biphasic AP?

  1. Rest: No potential difference between electrodes. 2. Depolarization: Upward deflection as wave reaches 1st electrode. 3. Return to zero: Potential difference returns to zero. 4. Downward deflection: Downward deflection as wave passes 2nd electrode.
Signup and view all the flashcards

What is depolarization?

A phase where the membrane potential becomes less negative, due to sodium ions (Na+) rushing into the nerve fiber.

Signup and view all the flashcards

Explain repolarization.

A phase where the membrane potential returns to its resting state due to potassium ions (K+) flowing out of the nerve fiber.

Signup and view all the flashcards

What are Electrotonic potentials?

Small, passive changes in membrane potential, spreading locally from the stimulus.

Signup and view all the flashcards

Explain the role of Voltage-gated K+ channels.

They open during repolarization, allowing potassium ions to flow out and restore the negative charge inside the nerve.

Signup and view all the flashcards

Why does the AP obey the 'all or nothing' rule?

Once the firing level is reached, a full action potential is triggered, regardless of the stimulus strength.

Signup and view all the flashcards

Velocity of Conduction

The speed at which a nerve impulse travels along a nerve fiber. Factors like distance and fiber type influence it.

Signup and view all the flashcards

Sodium Channel Closure

During repolarization, voltage-gated sodium channels close, stopping the influx of sodium ions into the cell.

Signup and view all the flashcards

Potassium Channel Opening

Voltage-gated potassium channels open during repolarization, allowing potassium ions to flow out of the cell. This helps restore the negative charge inside the cell.

Signup and view all the flashcards

Why Hyperpolarization Happens?

After repolarization, potassium channels close slowly, causing too much potassium to leave the cell. This temporary drop below the resting membrane potential is called hyperpolarization.

Signup and view all the flashcards

What does the Na-K pump do?

The Na-K pump actively transports sodium ions OUT of the cell and potassium ions IN to maintain the concentration gradients required for the resting membrane potential.

Signup and view all the flashcards

Spike Potential Phases

The rapid depolarization during an action potential has two phases: slow depolarization, when the membrane potential gradually rises, and rapid depolarization, when the membrane potential rapidly increases.

Signup and view all the flashcards

Afterpotential Types

After the spike potential, there are two types of afterpotentials: Negative Afterpotential, a slight depolarization due to slow potassium efflux, and Positive Afterpotential, a slight hyperpolarization due to slow potassium channel closure.

Signup and view all the flashcards

Depolarization Wave & Second Electrode

When the depolarization wave passes the second electrode, it causes a downward deflection in the recording.

Signup and view all the flashcards

What are the four main phases of a biphasic AP?

  1. Rest: No potential difference between electrodes. 2. Depolarization: Upward deflection as wave reaches 1st electrode. 3. Return to zero: Potential difference returns to zero. 4. Downward deflection: Downward deflection as wave passes 2nd electrode.
Signup and view all the flashcards

'All or Nothing' Rule

Once the firing level is reached, a full action potential is triggered, regardless of the stimulus strength. It either happens fully or not at all.

Signup and view all the flashcards

What is the Na-K pump?

This is a protein that acts like a pump, actively transporting sodium ions (Na+) out of the cell and potassium ions (K+) into the cell. This helps maintain the ion gradients necessary for the resting membrane potential.

Signup and view all the flashcards

Monophasic AP

This is a type of action potential recording where a single, upward deflection is observed. It's obtained by placing one recording electrode inside the nerve fiber and another reference electrode outside.

Signup and view all the flashcards

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

Studying That Suits You

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

Quiz Team

Related Documents

Physiology Lecture (14) PDF

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser