Neuroscience Chapter on Action Potentials

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Questions and Answers

What is the main function of the refractory period in nerve fibers?

It ensures impulses flow in both directions.

It limits the rate of impulses to 500-1000 per second. (correct)

It increases the rate of impulses along a fiber.

It enhances the resting potential of the fiber.

What happens during the absolute refractory period?

The nerve fiber can be restimulated by a weaker stimulus.

It is impossible to restimulate the fiber. (correct)

The sodium ion channels are completely open.

The axon can conduct impulses in either direction.

What is primarily responsible for restoring the resting potential after an action potential?

Sodium/potassium pump and membrane permeability to potassium ions. (correct)

Chloride ions and their influx.

Calcium ions and their channels.

Magnesium ions and their diffusion.

What initiates the wave of depolarization in a neurone?

The diffusion of sodium ions into the neurone. Signup and view all the answers

In what time frame does the absolute refractory period occur?

Immediately after the action potential. Signup and view all the answers

What characterizes the relative refractory period?

A stronger stimulus is needed to re-stimulate the axon. Signup and view all the answers

What does the recovery time of an axon refer to?

The refractory period. Signup and view all the answers

How does the refractory period affect impulse direction along nerves?

It ensures impulses flow in only one direction. Signup and view all the answers

What triggers the opening of sodium ion channels in the next region of the neurone?

The diffusion of sodium ions from the previous region. Signup and view all the answers

What happens to the permeability of the axon membrane during depolarization?

It increases specifically to sodium ions. Signup and view all the answers

What is the potential difference across the membrane at the peak of the action potential?

+40 mV Signup and view all the answers

What occurs immediately after depolarization in the action potential process?

Potassium ions rapidly diffuse out of the axon. Signup and view all the answers

What defines the threshold for triggering an action potential?

The opening of sufficient sodium ion channels. Signup and view all the answers

What is the duration of the depolarization phase in the action potential?

Approximately 1 millisecond Signup and view all the answers

What is the typical shape of the oscilloscope trace during an action potential referred to as?

Spike Signup and view all the answers

Why do potassium ions diffuse out of the axon during repolarization?

They are repelled by the positive charge inside the axon. Signup and view all the answers

What mechanism restores the resting potential after an action potential?

Pumping of excess sodium ions out of the axon. Signup and view all the answers

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

The action potential can vary in amplitude based on the stimulus. Signup and view all the answers

During which phase does the inside of the axon become negative relative to the outside again?

Repolarization phase Signup and view all the answers

Study Notes

Action Potential Overview

Impulse along an axon changes cell membrane permeability to sodium ions due to stimuli or neurotransmitters.
Experimental stimulation often involves controlled electrical impulses.

Depolarization Phase

Stimulation increases axon membrane's permeability to sodium ions.
Sodium ion channels open, allowing rapid diffusion of sodium ions, reversing membrane potential briefly.
Depolarization lasts approximately 1 millisecond, peaking at about +40mV, known as the action potential.
This process occurs in all nerve fibers, not just axons.

Repolarization Phase

Sodium channels close post-depolarization; excess sodium is pumped out.
Voltage-dependent potassium channels open, allowing potassium ions to diffuse out.
Inside of the axon becomes negatively charged again, restoring the resting potential over a few milliseconds.

Action Potential Recording

Action potentials can be recorded with an internal/external electrode setup using an oscilloscope.
Oscilloscope trace appears as a 'spike', illustrating potential differences during sodium influx and resting potential recovery.

Threshold and All-or-Nothing Response

Threshold is reached when sufficient sodium channels open, allowing sodium influx to surpass potassium outflow.
The action potential is an all-or-nothing response; its magnitude remains consistent regardless of stimulus strength.

Refractory Period

Crucial for nervous system function, limiting impulse flow to 500-1000 per second and ensuring unidirectional impulse propagation.
The refractory period includes two phases:
- Absolute refractory period: Initial phase post-action potential where restimulation is impossible due to blocked sodium channels.
- Relative refractory period: Occurs after absolute, where stronger stimuli are needed for re-stimulation.

Propagation of Action Potential

Action potential spreads along the neuron as a wave of depolarization:
- Sodium ions entering cause adjacent sodium channels to open.
- This initiates sodium influx in nearby regions, creating a continuous wave.
- The wave moves away from refractory membrane areas that cannot initiate new action potentials.

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Description

Explore the mechanisms of action potentials in neurons, including the depolarization and repolarization phases. Understand how sodium and potassium ions play a crucial role in this electrical signaling process. This quiz will test your knowledge of neuronal impulse transmission and its physiological implications.