How does the sodium-potassium pump help to establish the resting potential?

It actively transports three sodium ions out of the axon for every two potassium ions brought in, using ATP, so more positive charge leaves than enters.

What is meant by the threshold potential?

It is the membrane potential, around −55 mV, that must be reached before voltage-gated sodium channels open fully and an action potential is triggered.

Explain why depolarisation is described as a positive feedback process.

Sodium entering the axon depolarises the membrane further, and that depolarisation opens still more voltage-gated sodium channels, so entry accelerates until the peak is reached.

OCR A-Level Biology B H422

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The Nervous System and the Identification and Consequences of Damage

Resting potential and the action potential

3 things to know
Components 01, 02 and 03

Overview

Recall questions on the resting potential of about −70 mV and the sodium-potassium pump, threshold, depolarisation as positive feedback, repolarisation and hyperpolarisation, the all-or-nothing principle, refractory periods, saltatory conduction along myelinated axons, and calculating conduction speed.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

What is the resting potential of an axon, how is it maintained, and how is the strength of a stimulus represented?

Key term

State the typical value of the resting potential of a neurone.

Key term

Why does potassium leak out of a resting axon faster than sodium leaks in?

Questions from this subtopic

Each one with the model answer underneath.

1
State the typical value of the resting potential of a neurone.
Model answer
The resting potential is about −70 mV, with the inside of the axon negative relative to the outside.
2
How does the sodium-potassium pump help to establish the resting potential?
Model answer
It actively transports three sodium ions out of the axon for every two potassium ions brought in, using ATP, so more positive charge leaves than enters.
3
Why does potassium leak out of a resting axon faster than sodium leaks in?
Model answer
The resting membrane has many more open potassium channels than sodium channels, so it is far more permeable to potassium ions.
4
What is meant by the threshold potential?
Model answer
It is the membrane potential, around −55 mV, that must be reached before voltage-gated sodium channels open fully and an action potential is triggered.
5
Explain why depolarisation is described as a positive feedback process.
Model answer
Sodium entering the axon depolarises the membrane further, and that depolarisation opens still more voltage-gated sodium channels, so entry accelerates until the peak is reached.
6
To roughly what value does the membrane potential rise at the peak of an action potential?
Model answer
It rises to about +40 mV.

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Resting potential and the action potential

Overview

What you need to know

What is the resting potential of an axon, how is it maintained, and how is the strength of a stimulus represented?

State the typical value of the resting potential of a neurone.

Why does potassium leak out of a resting axon faster than sodium leaks in?

Questions from this subtopic

State the typical value of the resting potential of a neurone.

How does the sodium-potassium pump help to establish the resting potential?

Why does potassium leak out of a resting axon faster than sodium leaks in?

What is meant by the threshold potential?

Explain why depolarisation is described as a positive feedback process.

To roughly what value does the membrane potential rise at the peak of an action potential?

Other ways to work this

What is inside Levo

The 3-step method, run for you

Cram a whole paper in one sitting

Blank Blitz makes facts automatic

Build It gets the exam shape right

Test It catches misconceptions

Brain Breaks between sessions

Every question in The Nervous System and the Identification and Consequences of Damage, on a schedule.