IUBio

question on ACTION POTENTIALS!

Eric Blanc eric at afmb.cnrs-mrs.fr
Tue Jan 19 02:49:14 EST 1999


Matt Jones wrote:
> [SNIP]
> 
> So that's it.

Bill Skaggs wrote:
[SNIP]

>I hope this helps.  If you want more information, you should consult a
>textbook.

Richard Norman wrote:
[SNIP]
> I am sorry to be so long in answering.  However I know from years of
> experience
> in teaching this stuff that it is very tricky, indeed.


Thanks to all 3 contributors. It was a great thread...


I'd like to complicate the the system:

I learned the perfect model from Hodgkin and Huxley.
And it works fine:
Depolarization causes Voltage-sensitive Sodium channels to open,
This creates the Action potential. Then, Sodium channels inactivate, and
in the same time, delayed rectifier Voltage sensitive potassium channel
opens, which bring back the membrane potential to its resting value.
That's not the end of the action potential.
AP terminates with an hyperpolarization phase, which results from the
opening of calcium activated potassium channels. Large-conductance
calcium activated potassium channels are responsible for the fast
after-hyperpolarization phase, and small-conductance calcium-activated
potassium channels are responsible for the slow AHP.

Why is it so rare to talk about this last process ?

Moreover, nerve fibers are myelinidated in vertebrates. Action
potentials are not continuous all along the fiber, but jump from one
node to another.
To further complicate  this model, potassium channels are absent from
the nodes.
Action potentials are faster and more efficient, due to these reasons.
But Neuronal action potentials are somewhat different from those evoked
above.
Really tricky.

Eric.

--
_________________________________________________________________
Eric Blanc
	    NMR Group Postdoc., Webmaster for AFMB
WWW:   http://afmb.cnrs-mrs.fr/~eric/    AFMB CNRS-UPR 9039
Email: eric at afmb.cnrs-mrs.fr              31 Ch J. Aiguier
Fax: 33-4-91-16-45-36                     13402 Marseille CEDEX 20
Phone: 33-4-91-16-45-29                  FRANCE



More information about the Neur-sci mailing list

Send comments to us at biosci-help [At] net.bio.net