Neurophysiology: Action Potential Recording

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Questions and Answers

What initiates the rapid depolarization during the action potential?

Sudden opening of voltage-sensitive Na+ channels (correct)

Gradual K+ efflux from the cell

Calcium influx through voltage-sensitive channels

Chloride ion efflux from the neuron

Which phase of the action potential is characterized by the influx of Na+ ions?

Repolarization stage

Negative after-potential

Latent period

Depolarization stage (correct)

What characterizes the negative after-potential phase of the action potential?

Increased K+ permeability causing further repolarization (correct)

A slight overshoot in membrane potential

A decrease in K+ permeability

Increased Na+ influx

What occurs during the ascending limb of the spike potential?

Na+ influx begins and causes depolarization Signup and view all the answers

Which of the following best describes the mechanism of repolarization during the action potential?

K+ ions exit the cell leading to restoration of resting potential Signup and view all the answers

What is the outcome of the action potential's overshoot phase?

The membrane potential reaches a peak of +35 mV Signup and view all the answers

During what interval does the impulse travel toward the recording electrode?

Latent period Signup and view all the answers

Which of the following statements about the action potential is false?

Depolarization is purely due to K+ efflux. Signup and view all the answers

What primarily initiates the depolarization phase of the action potential in neurons?

Inward flux of Na+ ions Signup and view all the answers

Which of the following phases is characterized by the rapid decline of membrane potential after reaching its peak during an action potential?

Repolarization phase Signup and view all the answers

What is the key ionic change that occurs during the repolarization phase of an action potential?

Increased K+ conductance Signup and view all the answers

What defines the after potential following an action potential?

It is a period of prolonged hyperpolarization. Signup and view all the answers

During the action potential, what generally triggers the opening of voltage-gated Na+ channels?

Threshold depolarization Signup and view all the answers

How do the Na+/K+ pumps contribute to the overall action potential process?

They reset the resting membrane potential after an action potential. Signup and view all the answers

What role does the presence of negatively charged proteins inside the cell play in resting membrane potential?

It helps maintain the negativity of the membrane potential. Signup and view all the answers

Which event marks the peak of the action potential?

Inactivation of sodium channels Signup and view all the answers

What primarily triggers repolarization in a neuron's action potential?

K+ efflux through immediately opened voltage-sensitive K+ channels Signup and view all the answers

At what membrane potential do the sodium channels begin to activate during depolarization?

-55 mV Signup and view all the answers

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

It reaches resting membrane conditions after depolarization Signup and view all the answers

What occurs during the after potential phase after a neuron's action potential?

The rate of repolarization reduces when 70% repolarized Signup and view all the answers

How does sodium influx specifically affect the membrane potential during depolarization?

It results in a momentary reversal of polarity to +35 mV Signup and view all the answers

Which component of the Na+ channel is responsible for its voltage-gated nature?

The presence of both gates that respond to membrane potential Signup and view all the answers

What characterizes the spike potential phase of an action potential?

It features a rapid increase in Na+ concentration resulting in a sharp rise Signup and view all the answers

What primarily influences the duration of small waves during after potentials?

Rate of repolarization and membrane potential reduction Signup and view all the answers

Study Notes

Threshold Stimulus and Action Potential

Action potential can be recorded using cathode ray oscilloscope with microelectrodes; one is inserted into the nerve, and the other is positioned on its outer surface.
Stimulating the nerve generates a stimulus artifact due to current leakage, followed by a latent period representing the time taken for the impulse to reach the recording electrode.

Phases of Action Potential

Spike Potential consists of:
- Depolarization Stage: Upward shift in membrane potential due to Na+ influx.
- Repolarization Stage: Downward shift as K+ ions exit the cell.
- Negative After-Potential: Occurs after repolarization.
- Positive After-Potential: The brief period of elevated voltage following action.

Components of Action Potential

Spike Potential Duration: Occurs over a short span of 0.5 - 1 msec in myelinated fibers.
Ionic Changes during Depolarization:
- Ascending Limb: Na+ influx changes membrane potential from -70 mV (resting) to -55 mV (threshold).
- Rapid Na+ influx at the threshold leads to overshoot, pushing membrane potential to +35 mV, indicating reversal of polarity.

Mechanism of Ionic Movement

Repolarization: About 70% of the repolarization process involves K+ efflux following the rapid opening of voltage-sensitive K+ channels after Na+ channels close.

Ion Channel Dynamics

Na+ Channels:
- Composed of an activation gate on the outer membrane and an inactivation gate on the inner side.
- Voltage-gated; their opening and closure depend on the membrane potential.

Redistribution of Ions

Na+/K+ pump restores resting membrane potential by actively transporting Na+ out and K+ into the cell.

After Potentials

Types of After Potentials:
- Negative After Potential: Occurs upon reaching 70% of repolarization; resting potential is slowly restored.

Resting Membrane Potential (RMP)

Definition: The voltage difference across the cell membrane; in nerves, it is approximately -70 mV, maintained by K+ leak channels and negatively charged proteins within cells.
Na+/K+ pump helps in correcting disturbances to the resting membrane potential.

Definition of Action Potential

Action potential is defined as rapid changes in membrane potential during a threshold or suprathreshold stimulus, essential for the propagation of nerve impulses along the neuron.

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Description

This quiz focuses on the recording of action potentials in neurophysiology. It covers the methods used to measure action potentials with cathode ray oscilloscopes and microelectrodes, as well as the phases of action potential. Test your understanding of these fundamental concepts in nerve stimulation and signal recording.