Action Potential

Question 1

What is used to measure the speed of nerve fibres?

Answer 1

Change in extracellualr potential

Question 2

Axons within a fibres conduct at different speeds, true false

Answer 2

True

Question 3

Describe local current theory

Answer 3

There is a wave of depolarisation from the origin of the stimulus, (it travels along the axon). It causes immediate local change in the membrane potential.

Question 4

What is the length constant ?

Answer 4

The distance it takes a stimulus to fall 37% of the original.

Question 5

What things effect the speed of conduction of an action potential along a nerve fibre

Answer 5

Increasing diameter increases speed

Myelination also increases speed

Question 6

What is the role of the refractory period ?

Answer 6

Ensure unidirectional travel of an action potential. Also stops the positive feedback loop.

Question 7

What happens if the closing of K+ channels is delayed ?

Answer 7

This bring the membrane potential back to the negative faster increasing the rate of recovery from resting

Question 8

What is the myelin sheath?

Answer 8

Folds of membrane around the axon. This insulates increasing speed of action potential conduction.

Question 9

Describe the structure of a myelinated axon

Answer 9

Myelinated section and nodes of Ranvier. Action potential jumps from node to node allowing faster conduction. There are only ion channels at the nodes.

Question 10

Describe Saltatory conduction

Answer 10

The wave of depolarisation travels much further with myeline sheath. So the wave of depolarisation lasts from node to node staying above the threshold level even without the ion channels. Therefore much faster because ion channels opening and closing is slow.

Question 11

How does myeline change the relationship between conduction speed and diameter ?

Answer 11

Myelinated velocity is proportional to diameter

Non myelinated velocity is proportional to the square root of diameter.

Question 12

Give a disease that effects the nerves and action potentials

Answer 12

MS multiple sclerosis

Question 13

What causes MS?

Answer 13

Demyelination

Question 14

Describe myelinated and the effect it has in the body

Answer 14

The myeline is damaged which reduces the length constant so the depolarisation doesn’t reach to the next node and is under the threshold value so action potentials are not conducted.
This means reduced muscular movement ability but the effects depend on where the damaged myelinated sheaths are,

Question 15

Describe the generation of the action potential

Answer 15

Depolarisation above the threshold opens many voltage gated Na+ channels.
Influx of Na+ causes membrane potential to move towards Ena (depolarisation)
Na+ channels are inactivated and voltage gated K+ channels open
Influx of K+ causes repolarisation (moves towards Ek

Question 16

Describe conduction of an action potential

Answer 16

Action potential causes local depolarisation.
When this reaches the threshold an action potential is initiated
At nodes of ranvier axon is bare and high concert of Na+ channels
Action potential jumps from node to node (saltatory conduction)