The importance of the refractory period in impulse transmission

I'm towards the end of my revision on nerve impulse transmission and have come across two points in my class notes which I do not understand. I'll post the section below highlight in bold what I do not understand. It would be much appreciated if somebody could explain them to me :smile:

thankyou!!!

When an action potential has just taken place at a particular point in a neuron, that point is unable to fire another action potential immediately. the time while the membrane is unable to respond to another depolarisation is called the refractory period. During this time, the sodium ion voltage gated channels are not capable of opening. The refractory period is important for two reasons:
1. the action potential can only be propagated in one direction, thus preventing it from spreading in both directions along the neuron
2. a second action potential will be separated from the first by the refractory period that sets an upper limit to the frequency of impulses along the neuron

Thanks for any help :smile:

Reply 1

barrinalo

7

The refractory period is the time period where the voltage gated ion channels in the neuron membrane become unresponsive.

A nerve impulse is propagated by the continuous activation of these ion channels in adjacent sections of the axon in the direction of the nerve impulse.

So imagine that at a particular point of the axon the ion channels open and sodium ion diffuses in. The sodium ions will diffuse both ways along the axon, in the same direction as the impulse and the opposite direction as well. They will depolarise the membrane sections that are nearby. However, because of the refractory period, the voltage gated ion channels that are in the opposite direction of the impulse will be unresponsive, so they wont open and allow sodium to enter. The ion channels in the direction of the impulse have not yet been activated, so they will be activated, allowing sodium ions to rush in and repeat the cycle. As such, the refractory period prevents the backward propagation of an impulse.

Similarly, if a section of the axon has already been activated, another impulse cannot be sent as it would be unresponsive.

Reply 2

jessica_anne_clu

OP

2

Original post by barrinalo

The refractory period is the time period where the voltage gated ion channels in the neuron membrane become unresponsive.

A nerve impulse is propagated by the continuous activation of these ion channels in adjacent sections of the axon in the direction of the nerve impulse.

So imagine that at a particular point of the axon the ion channels open and sodium ion diffuses in. The sodium ions will diffuse both ways along the axon, in the same direction as the impulse and the opposite direction as well. They will depolarise the membrane sections that are nearby. However, because of the refractory period, the voltage gated ion channels that are in the opposite direction of the impulse will be unresponsive, so they wont open and allow sodium to enter. The ion channels in the direction of the impulse have not yet been activated, so they will be activated, allowing sodium ions to rush in and repeat the cycle. As such, the refractory period prevents the backward propagation of an impulse.

Similarly, if a section of the axon has already been activated, another impulse cannot be sent as it would be unresponsive.

I had to read that a few times to understand it but I understand it now! However, which part relates to 'a second action potential will be separated from the rest by the refractory period that sets an upper limit to the frequency of impulses along the neuron'? :smile:

Reply 3

barrinalo

7

the last paragraph that I wrote.

resting neuron sends action potential down the axon.

ion channel proteins along axon get deactivated as the impulse propagates.

Until the channels recover another impulse cannot be sent, because all the channels are deactivated.