Q: dendrites/gates

r norman rsn_ at _comcast.net
Sat Mar 19 22:55:50 EST 2005

On Sun, 20 Mar 2005 09:43:05 +1100, Matthew Kirkcaldie
<m.kirkcaldie-remove at unsw.edu.au> wrote:

>In article <9olo31pls7o6bj89nbd2kfjukr2b9nuo53 at 4ax.com>,
> r norman <rsn_ at _comcast.net> wrote:
>> Of course, passive potentials spread with decay, and can only travel a
>> few space constants before attenuating so severely that they can be
>> ignored.
>Aha!  But what about sodium and calcium spikes?  They can ensure 
>propagation of supposedly "passive" dendritic signals across several 
>millimetres ... otherwise there would be no point in having dendrites 
>that large.
>There are some fantastic papers from Greg Stuart and Michael Hausser 
>about the kinds of signals which get through from distal parts of the 
>dendrite tree - inputs to the apical dendrite, for example, can largely 
>be ignored, but under certain patterns of activity they can generate 
>spikes so large that they dominate any other inputs to the cell ...
>I know you know this (and I know a spike isn't a "passive potential" as 
>you were discussing), but I thought I would add it to your authoritative 
>summary for others' benefit.
>      Cheers, MK.

That is a very good point.  Many people don't realize that dendrites
can contain "hot spots" of electrical excitability -- that is, the
ability to make a full or a partial action potential.  Whether Na or
Ca, that doesn't matter as far as the electrical events go -- they are
both active potentials.  They do differ significantly in other
aspects, though.  The Calcium that enters through voltage gated
channels can act as a second messenger causing all kinds of
interesting events inside dendrites!

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