otrivine
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Why does prolonged depolarisation cause sodium inactivation?

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Asklepios
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(Original post by otrivine)
Why does prolonged depolarisation cause sodium inactivation?

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Remember that voltage-gated sodium channels exist in three states - open, closed (but activated), and inactivated. In the normal action potential, a depolarising stimulus opens sodium channels, which then inactivate after 1-2 milliseconds. This combined with potassium channels opening repolarises the cell.

However, if there is prolonged depolarisation the membrane potential will constantly be above the threshold for voltage-gated sodium channels which stimulates them to open. Remember they can only remain open for 1-2 milliseconds before inactivating, so they will be constantly inactivated.


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otrivine
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(Original post by Asklepios)
Remember that voltage-gated sodium channels exist in three states - open, closed (but activated), and inactivated. In the normal action potential, a depolarising stimulus opens sodium channels, which then inactivate after 1-2 milliseconds. This combined with potassium channels opening repolarises the cell.

However, if there is prolonged depolarisation the membrane potential will constantly be above the threshold for voltage-gated sodium channels which stimulates them to open. Remember they can only remain open for 1-2 milliseconds before inactivating, so they will be constantly inactivated.


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I see thant makes perfect sense. Thank you.

Another question, there are electrical and chemical synapses. When do we get these such as, should there be speicific stimuli for an electrical synapse to be involved. Like how can we determine if something will undergo electrical or chemical synapse?If you see what I mean.
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(Original post by otrivine)
I see thant makes perfect sense. Thank you.

Another question, there are electrical and chemical synapses. When do we get these such as, should there be speicific stimuli for an electrical synapse to be involved. Like how can we determine if something will undergo electrical or chemical synapse?If you see what I mean.
Electrical and chemical synapses are anatomically distinct. The vast majority of synaptic connections in the human body are chemical synapses, with a few electrical synapses. Electrical synapses allow greater speed of transmission, but there is a problem with these. Remember that a small axon will tend to synapse with a larger cell body, and so there will be a switch from a high resistance (and so low current) to a low resistance (high current) system. This means some form of chemical amplification is needed to trigger an action potential in the second cell. An important function of a chemical synapse is to create this gain.
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