15.4: Speed of the nerve impulse

Question 1

Factors affecting the speed at which an action potential travels
3

Answer 1

The myelin sheath
The diameter of the axon
Temperature

Question 2

How does the myelin sheath affect the speed at which an action potential travels

Answer 2

Action potentials jump between nodes of ranvier (saltatory conduction) which increases the speed of conductance in myelinated neurones.

Question 3

How does the diameter of the axon affect the speed at which an action potential travels

Answer 3

The grater the diameter of an axon, the faster the speed of conductance. This is due to less leakage from a large axon.

Question 4

Leakage from an axon means that

Answer 4

Membrane potentials are harder to maintain.

Question 5

How does the temperature affect the speed at which an action potential travels

Answer 5

Affects rate of diffusion of ions, therefore the higher the temp, the faster the nerve impulse.

Question 6

Threshold value

Answer 6

A certain level of stimulus which triggers an action potential.

Question 7

Nerve impulses often described as

Answer 7

All-or-nothing responses

Question 8

When are action potentials not generated?

Answer 8

If the stimulus is below the threshold value.

Question 9

How can the size of a stimulus be detected by an organism?

2

Answer 9

• by the number of impulses passing in a given time, the larger the stimulus, the more impulses in a given time
• by having different neurones with different threshold values

Question 10

The refractory period

Answer 10

The period of time after an action potential has been created in any region of an axon when inward movement of Na+ ions is prevented because Na+ voltage-gated channels are closed.
= impossible for a further action potential to be generated.

Question 11

Purpose of the refractory period

3

Answer 11

• It ensures that action potentials are propagated in one direction only
• it produces discrete impulses
• it limits the number of action potentials

Question 12

The refractory period ensures that action potentials are propagated in one direction only…

Answer 12

Prevents action potentials from spreading out in both directions.

Question 13

The refractory period only produces discrete impulses…

Answer 13

Ensures action potentials are separated from each other.

Question 14

The refractory period limits the number of action potentials…

Answer 14

Limits the strength of stimulus that can be detected.