Spiker

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so apparently the mylinated cell can also increase in the frequency of action potential. How exactly does that happen?
 

Hemichordate

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Action potentials can skip from Node of Ranvier to Node of Ranvier, which makes it faster.
 

G1SG2

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so apparently the mylinated cell can also increase in the frequency of action potential. How exactly does that happen?
Action potentials don't occur at the myelinated region. They only occur at the nodes of ranvier, as the above poster said. So suppose this is an unmyelinated axon, and the action potential is traveling down the entire length of the axon:

Action Potential -------------->

Compare it to an myelinated axon:

Action Potential --========--=======---========-->

The = is the myelinated portion of the axon, which the action potential doesn't travel on. So it just jumps over it to the other node (-) of ranvier.
 

sv3

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Action potentials don't occur at the myelinated region. They only occur at the nodes of ranvier, as the above poster said. So suppose this is an unmyelinated axon, and the action potential is traveling down the entire length of the axon:

Action Potential -------------->

Compare it to an myelinated axon:

Action Potential --========--=======---========-->

The = is the myelinated portion of the axon, which the action potential doesn't travel on. So it just jumps over it to the other node (-) of ranvier.

I don't quite agree about it increasing frequency. It can increase the speed of one action potential, but isn't the frequency determined more so by the refractory period? Perhaps its both but if I had a question that asked "does mylenation increase frequency?" I would have said no, because the refractory period is a huge factor in all this.

Unless of course.......the underlying assumption is that the faster an AP, the faster you start and finish the refractory period.........and get to fire another AP away.....perhaps this is what the question means??
 

G1SG2

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I don't quite agree about it increasing frequency. It can increase the speed of one action potential, but isn't the frequency determined more so by the refractory period? Perhaps its both but if I had a question that asked "does mylenation increase frequency?" I would have said no, because the refractory period is a huge factor in all this.

Unless of course.......the underlying assumption is that the faster an AP, the faster you start and finish the refractory period.........and get to fire another AP away.....perhaps this is what the question means??
Yeah, the myelination increases the speed. The frequency can be increased if the stimulus intensity is increased, but the magnitude and duration doesn't change (all or none response).
 

sv3

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Yeah, the myelination increases the speed. The frequency can be increased if the stimulus intensity is increased, but the magnitude and duration doesn't change (all or none response).
Not sure about the increased frequency. There was a question in TPR's content book comparing myelination vs unmyelinated neurons and they specifically said frequency isn't greater in the myelinated neurons b/c the refractory period doesn't change. The voltage gated channels are the same on both types of neurons and they are "in charge" of the refractory time. So i don't think its correct to say frequency is greater without alot more info. Speed for sure, not frequency...at least i think so

just my two cents
 

RogueUnicorn

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frequency is dictated by the mandatory refractory period of rebuilding the potential through the Na/K pump. the myelination has no effect on frequency.
 

G1SG2

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Yup, the myelination doesn't affect frequency. I meant in general, if the stimulus intensity were to increase, then the frequency can increase.
 

sv3

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Yup, the myelination doesn't affect frequency. I meant in general, if the stimulus intensity were to increase, then the frequency can increase.
Yeah I think your right on. It's not a matter of myelinated vs unmyelinated but rather how long can you continue to fire action potentials for. The longer you can fire APs, the more times you will get one across.

Fire an AP, wait for recfractory, fire an AP. That order can't change. So if comparing two neurons, it seems to be a matter of which can outlast the other. OR at least that's what im thinking....but no expert here