Neurone Excitability

Question 1

Stages of an action potential

Answer 1

Depolarisation
Repolarisation
Hyperpolarisation

Question 2

What happens during depolarisation

Answer 2

Voltage gated Na+ ion channels open.
This increases the conductance of Na+ leading to an influx into the axon.
In turn, this increases the membrane potential
This leads to threshold potential
This results in all Na+ gated channels to open so the Em is now 40mV.

Question 3

What happens during depolarisation?

Answer 3

Na+ gated channels are inactivated and voltage gated K+ channels open. This increases the permeability to K+ so they efflux.

Question 4

What happens during hyper polarisation.

Answer 4

The voltage gated K+ channels remain open after Em is returned. This causes Em to approach Ek. Eventually the channels close and Em is reestablished via leak channels.

Question 5

How can the strength of a response be increased?

Answer 5

Increasing the number of action potentials

Question 6

Two types of refractory period

Answer 6

Absolute and Relative

Question 7

What is an absolute refractory period?

Answer 7

The absolute refractive period occurs when gated K+ channels are still ope.
Many of the Na+ Channels are inactivated thus another AP cannot occur

Question 8

What is a relative refractory period?

Answer 8

This occurs as some K+ channels are still open whilst Na+ channels are inactivated (to allow time to recover). As a result, a larger stimulus is required to open sufficient Na+ channels. This means that the threshold potential is effectively higher

Question 9

Why does a myelinated axon conduct an impulse faster than an unmyelinated axon?

Answer 9

The myelin sheath prevents conduction along the axon. As a result, the action potential jumps to the adjacent nodes of Ranvier.
This is known as saltatory conduction

Question 10

What three things affect the speed of conduction?

Answer 10

Myelination
Diameter
Temperature