Neuroscience: Action Potentials

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Questions and Answers

What triggers the opening of voltage-gated Na+ channels during the depolarization phase of an action potential?

Decrease in Na+ concentration outside the cell

Inactivation of K+ channels

Increased permeability of K+ ions

Membrane potential reaching the threshold (correct)

Which characteristic of action potentials reflects the all-or-none principle?

Action potentials can be graded in strength

Action potentials only occur in response to strong stimuli

Action potentials can vary in size depending on the stimulus strength

Action potentials are always the same amplitude and duration (correct)

What occurs during the absolute refractory period of an action potential?

K+ channels close enabling excitability.

Na+ channels are inactive and cannot be opened. (correct)

The membrane is in a state of depolarization.

Action potentials can be generated with weaker stimuli.

How does hyperpolarization affect the membrane potential?

It results in a more negative membrane potential than resting potential. Signup and view all the answers

What interrupts the positive feedback loop during the rising phase of the action potential?

Inactivation of voltage-gated Na+ channels Signup and view all the answers

Which statement correctly describes the all-or-none principle?

All action potentials are of a fixed size regardless of the current produced. Signup and view all the answers

What is a primary function of voltage-gated K+ channels during the repolarization phase?

To restore the membrane potential back to resting state Signup and view all the answers

During the refractory period, what is the state of the voltage-gated Na+ channels?

They are inactivated and cannot conduct ions Signup and view all the answers

During which period can an action potential be triggered only by stronger than normal stimuli?

Relative refractory period Signup and view all the answers

What happens to the membrane potential during hyperpolarization?

It becomes more negative than resting potential Signup and view all the answers

What primarily causes the refractory periods following an action potential?

Inactivation of Na+ channels and increased K+ channel opening. Signup and view all the answers

What effect does a greater intensity of stimulation have on action potential frequency?

It can increase the frequency of firing. Signup and view all the answers

What is the role of the slow response of voltage-gated K+ channels during an action potential?

To facilitate gradual repolarization Signup and view all the answers

Which of the following best describes the role of voltage-gated channels during the action potential?

They allow Na+ influx followed by K+ efflux. Signup and view all the answers

What occurs immediately after an action potential is generated?

Hyperpolarization of the neuron's membrane Signup and view all the answers

What happens to the K+ channels by the end of hyperpolarization?

All K+ channels are closed. Signup and view all the answers

What is the primary function of voltage-gated Na+ and K+ channels during an action potential?

To initiate depolarization and repolarization of the neuron Signup and view all the answers

During which phase of the action potential does the membrane potential reach its highest value?

Depolarization phase Signup and view all the answers

Which statement best describes the all-or-none principle in action potentials?

An action potential either occurs fully or not at all once threshold is reached Signup and view all the answers

What characterizes the refractory period during and after an action potential?

The inability of the neuron to fire another action potential under certain conditions Signup and view all the answers

What effect does hyperpolarization have on a neuron?

It decreases the membrane potential, making it more negative Signup and view all the answers

Which of the following correctly describes the sequence of ionic movements during the action potential?

Na+ enters the cell, followed by K+ exiting the cell Signup and view all the answers

Which of these best defines the threshold potential in neurons?

The minimum membrane potential needed to trigger an action potential Signup and view all the answers

How does the sodium-potassium pump contribute to the action potential process?

By maintaining the resting membrane potential after an action potential Signup and view all the answers

Study Notes

Action Potential

An action potential, a rapid change in membrane potential, is generated at the threshold
The minimum amount of depolarization needed to trigger an action potential is called the threshold, typically -55mV
Action potentials are all-or-none events, meaning they either occur fully or not at all
The amplitude and duration of action potentials are consistent
Weak stimuli don't produce an action potential

Depolarization

Depolarization, where the cell becomes more positive, starts when the threshold is reached
This opens voltage-gated sodium (Na+) channels, allowing more Na+ to flow into the cell
Increased Na+ influx further depolarizes the cell, opening more Na+ channels creating a positive feedback loop
This positive feedback loop drives the rising phase of the action potential

Repolarization

The rising phase of the action potential ends when the positive feedback loop is interrupted:
- Voltage-gated Na+ channels inactivate after a certain time, closing
- Voltage-gated potassium (K+) channels, responding slowly to depolarization, start to open
The slow opening of K+ channels allows K+ to move out of the cell, making the cell more negative (repolarizing)
The membrane potential becomes more negative than the resting membrane potential, a state called hyperpolarization

Refractory Period

The action potential is followed by a refractory period, a brief period of decreased excitability
The refractory period is divided into two phases:
- Absolute refractory period: the cell cannot be stimulated to fire another action potential, regardless of stimulus strength
- Relative refractory period: the cell can be stimulated to fire another action potential, but only by a stronger stimulus than usual
The refractory periods are caused by the inactivation of Na+ channels and increased opening of K+ channels

All-or-None Principle

Action potential amplitude is independent of the stimulus strength.
A stronger stimulus does not produce a larger action potential but can trigger more frequent firing.

Action Potential Conduction

Electrical currents across cell membranes are carried by ions like sodium (Na+) and potassium (K+)

Action Potential Initiation

Signals from dendrites and the cell body reach the axon hillock
If these signals cause the membrane potential at the axon hillock to depolarize past the threshold, an action potential is triggered

Nobel Prize in Physiology or Medicine (1963)

Alan L. Hodgkin and Andrew F. Huxley shared the Nobel Prize in Physiology or Medicine for their quantitative description of the ionic currents involved in the action potential.
They used voltage-clamp recordings to study the ionic currents in the squid giant axon.

Threshold

If the stimulus reaching the axon hillock is strong enough, the neuron depolarizes by approximately 15mV and reaches the threshold.

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Description

Test your knowledge on the mechanics of action potentials in neuroscience. Explore key concepts such as depolarization, threshold levels, and the all-or-nothing principle of action potentials. This quiz covers essential principles that underpin neural signaling.