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neurology

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neurology

Postby jwalin » Sun Nov 22, 2009 4:08 am

i have 3 questions. of which 3rd seems nearly solved.

why do thick nerves conduct impulses faster than thinner? :?:
is it because ther are more membranes across which the potentials can be set up.

why do mylinetyed axons conduct faster than non myllinated of the same diameter. :?:
is it because the current jumps?

when an action potential travels then how are local currents set up if the ions do not move
is it because of the electrons. has to be. just confirming it. :oops:
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Postby jwalin » Sun Nov 22, 2009 4:24 am

i know for thesecond its called the saltatory conduction. but why does it increase the speed?
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Postby JackBean » Sun Nov 22, 2009 7:04 am

2) yeah, it's faster, because it jump through the myelin
3) and you thought, you have solved this one? :lol: No, why do you think, the ions should not move? I mean, they do not move along the nerve, but they are exchanged between intra- and extracellular space. Tha't the principle of excitment movement.
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Postby jwalin » Sun Nov 22, 2009 9:31 am

and for the first one am i right
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Postby Tamaroshka » Tue Nov 24, 2009 5:15 pm

the first one do you mean the axon's diameter ? if so then the answer is , the thicker the axon the faster the rate of transmission Of an impulse this is thought to be due to the greater surface area of axon membrane over which exchange of ions can occur ..
Giant axons are found in number of invertebrates including earthworms, marine annelids and crustaceans. They are thought to be associated with rapid escape responses, since rapid transmission of impulses is needed between receptors and muscles to withdraw the animal from danger.
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Postby chachi » Wed Dec 02, 2009 2:30 am

An action potential fires when the soma (cell body) reaches threshold. It is then, that the axon hillock begins to fire, this firing elicits a cascade of changes with the membrane potential. The voltage gated sodium channels open up, which depolarizes (make cell negative) the cell at that point in the axon hillock. This change in membrane potential causes the potassium channels to open up, which then causes the cell to repolarize (become slightly positive again). This process propagates all the way down the axon without going back the opposite direction due to the refractory period. These changes in electrochemical gradients (conductivity) sends charges down the axon, which is conserved by the myelination. However, if you have too much insulation on the axon, the charge may have trouble going down (resistance).
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