Nerve Impulses: Movement Of Action Potential

Question 1

Nerve impulse

Answer 1

Movement of the action potential (pos charge inside axon relative to outside a neurone due to Na+ ions) along the whole length of an axon

Question 2

In a non myelinated neurone, what is the first step to move the action potential towards the axon terminal end?

Answer 2

Na+ ions from depolarisation will diffuse into axon when threshold is met
Within axon, Na+ will diffuse sideways down electrochemical gradient to an area with low pos charge

Question 3

Local current

Answer 3

Diffusion of Na+ ions sideways down electrochemical gradient sideways within an axon

Question 4

Once a local current has been generated, what are we left with in the axon?

Answer 4

Accumulation of Na+ ions thus pos charge in an adjacent patch in the neurone under neurone membrane
Taking this patch to threshold potential

Question 5

What happens when the adjacent patch in the neurone under the neurone membrane is taken to threshold potential?

Answer 5

Voltage gated Na+ channel proteins open allowing Na+ ions to diffuse in to neurone and increase pos charge causing further depolarisation over the neurone membrane
Generates a new local current

Question 6

Local currents can move within a neurone…

Answer 6

Backwards and forwards: diffusion of Na+ ions down electrochemical grad toward cell body and toward axon terminal end

Question 7

Why can the action potential only move forward?

Answer 7

Due to the refractory period

Question 8

What is the refractory period?

Answer 8

The patch of neurone which just had the area of pos charge (but Na+ions diffused to next patch in the local current) is now repolarising from pos action potential back to resting neg potential
At this point voltage gated Na+ channel proteins SHUT

Question 9

Why does the refractory period prevent action potential flowing backwards?

Answer 9

Because action potential cannot be generated backward in the neurone as the voltage gated Na+ channel proteins SHUT so Na+ ions cannot flow into neurone at this point

Question 10

When can an action potential be restored again?

Answer 10

After refractory period once restored back to resting potential, however the action potential would have moved forward at this point so therefore it cannot flow backward