Nerve Impulses: Action Potential

Question 1

What is an action potential?

Answer 1

A brief reversal of the potential across the membrane of a neurone causing a peak of +40mV compared to the resting potential of -60mV.

Question 2

What is positive feedback?

Answer 2

A mechanism that increases a change taking the system further away from the optimum.

Question 3

What is the resting potential?

Answer 3

The potential difference across the membrane while the neurone is at rest.

Question 4

What does it mean if a neurone is at rest?

Answer 4

When a neurone is not transmitting an action potential.

Question 5

Why is the membrane more permeable to potassium ions than to sodium ions?

Answer 5

The potassium ion channels are always open so allow the movement of potassium ions across the membrane. Whereas the gated sodium ion channels are kept closed.

Question 6

What is another reason for the inside of the cell to remain negative?

Answer 6

The cell cytoplasm also contains large organic anions (negatively charged ions). Hence the interior of the cell at a negative potential compared with the outside.

Question 7

What is the value for the resting potential?

Answer 7

-60mV

Question 8

How are the neurone’s gated channels opened?

Answer 8

By the action of the synapse.

Question 9

What happens when the gated channels open?

Answer 9

A few sodium ions enter the cell which produces a small depolarisation. This is known as a generator potential.

Question 10

What are sodium gated channels also called?

Answer 10

Voltage-gated channels.

Question 11

How are voltage gated channels opened?

Answer 11

By slight changes in the potential difference of the membrane.

Question 12

How are generator potentials an example of positive feedback?

Answer 12

As more generator potentials are created to reach a threshold potential they cause the voltage-gated channels to open. A small depolarisation of the membrane causes a change which increases the depolarisation further.

Question 13

What happens as a result of the voltage-gated sodium ion channels opening?

Answer 13

It causes an influx of sodium ions and the depolarisation reaches =40mV. Once this value is reached the neurone will transmit the action potential.

Question 14

What does “the action potential is self-perpetuating” mean?

Answer 14

Once it starts at one pouint in the neurone, it will continue along to the end of the neurone. They are therefore referred to as all or nothing responses.

Question 15

What is the threshold value of the membrane before an action potential is created?

Answer 15

-50mV

Question 16

What is it called when the potential difference overshoots slightly?

Answer 16

Hyperpolarisation.

Question 17

How is the autoimmune disease multiple sclerosis associated with neurones?

Answer 17

Multiple sclerosis is caused by the the demyelination of the motor neurones. The neurones lose their myelin sheath and are unable to conduct impulses properly.