13.4

Question 1

What two types of neurone are there?

Answer 1

Myelinated and non-myelinated

Question 2

What is a myelinated neurone?

Answer 2

A neurone with a myelin sheath around the axon.

Question 3

Describe the myelin sheath that is present on some neurones.

Answer 3

Made of Schwann cells.
Nodes of Ranvier between Schwann cells.

Question 4

Describe the passage of the action potential in non-myelinated neurones. (5 marks)

Answer 4

1. Neurone is polarised
2. Neurone is stimulated, and the first section is depolarised (AP is set up)
3. A localised circuit (difference in charge) is set up between this section and the next
4. The sodium ions diffuse towards the negative region, this causes the gated sodium channels to open.
5. The second section is now depolarised too and the action potential is passed on
6. The AP is passed on again, and the first section is repolarised
7. This continues until the end of the neurone
8. There is a refractory period (when the section is repolarised) when the action potential cannot be passed on

Question 5

What is an localised circuit?

Answer 5

A difference in charge

Question 6

Why does the action potential pass on in the neurone?

Answer 6

The first section has more sodium ions
This creates a diffusion gradient and a difference in charge
The sodium ions diffuse to the next section
The gated sodium channel proteins open

Question 7

Describe the passing of action potential in a myelinated neurone.

Answer 7

The myelin sheath acts as an electrical insulator.
There are only sodium potassium voltage gated channel proteins in the nodes of Ranvier.
So the action potential jumps from node to node, this is called saltatory conduction.

Question 8

What 3 factors can affect the rate at which the action potential is transmitted?

Answer 8

Myelinated/ non-myelinated
Axon diameter width
Temperature

Question 9

Why is action potential transmitted faster when the axon diameter is wider?

Answer 9

Wider axon- the sodium ions are more likely to leak.

Question 10

Why is the action potential transmitted faster when the neurone is myelinated?

Answer 10

The voltage gated channel proteins only need to open at nodes of Ranvier, rather than all the way along the neurone.

Question 11

How does the brain detect how large the stimulus is?

Answer 11

The larger the stimulus, the more frequent the impulses are, and more receptors are activated.