username1160642
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morgan8002
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(Original post by sbzk101)
Hi guys, I'm doing AQA A2 biology and I don't understand how saltatory conduction works. I know that the myelin prevents ion exchange in myelinated neurones, and the Na+ ion channels are concentrated in the nodes of Ranvier, so only in the nodes can action potentials be propagated.

But what I don't get is how the action potential seems to 'jump' across adjacent nodes - I've been told it does, but I've never found a sufficient explanation. According to the diagram below, the nodes are electrically isolated from each other by the myelin, and AFAIK, ions can't just jump across the gap randomly (right?).

I would really appreciate your help.
Thanks in advance
The ions diffuse along inside of the neurone. This is how the action potential travels between nodes. They diffuse faster because the Myelin sheath keeps the Na+ concentration gradient high along the neurone.
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Asklepios
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(Original post by sbzk101)
Hi guys, I'm doing AQA A2 biology and I don't understand how saltatory conduction works. I know that the myelin prevents ion exchange in myelinated neurones, and the Na+ ion channels are concentrated in the nodes of Ranvier, so only in the nodes can action potentials be propagated.

But what I don't get is how the action potential seems to 'jump' across adjacent nodes - I've been told it does, but I've never found a sufficient explanation. According to the diagram below, the nodes are electrically isolated from each other by the myelin, and AFAIK, ions can't just jump across the gap randomly (right?).

I would really appreciate your help.
Thanks in advance
First consider an unmyelinated neurone and think of it as a hose through which ions flow. Most of the ions will flow through the hose till the end, but some will 'leak' out through the walls (or the cell membrane). This is why we have voltage gated ion channels in the membrane of a neurone - to amplify the action potential and maintain a constant 'ion flow' within the neurone.

Passive ion flow in an axon is a much quicker mode of transmission than opening up voltage gated ion channels every so often, but it's needed to amplify the signal.

Myelination of the axon insulates the membrane so minimises the 'leak' out of the membrane. Hence we don't need as regular amplification points, and instead can concentrate voltage gated ion channels at the nodes of ranvier. The jump is passive flow of ions between nodes and at each node the signal is amplified to maintain the action potential.


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morgan8002
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(Original post by sbzk101)
By the 'inside' do you mean the space that is covered by the myelin? Is the diagram I made to understand it correct?
Yes, by the inside I mean the cytoplasm of the neurone.
In an action potential, Na+ moves quickly into the cell, increasing the local Na+ concentration. The concentration back down the neurone is still high(where the signal came from), so the Na+ diffuses forward along the neurone towards the next node of Ranvier.
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