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Axon collaterals ?

r norman rsn_ at _comcast.net
Sun Jan 4 20:04:52 EST 2004


On Mon, 05 Jan 2004 00:02:03 GMT, Matthew Kirkcaldie
<Matthew.Kirkcaldie at removethis.newcastle.edu.au> wrote:

>In article <hvn9vv0ljsu5b4c2vmcro9rnjvltojrfst at 4ax.com>,
> r norman <rsn_ at _comcast.net> wrote:
>
>> On Fri, 02 Jan 2004 12:17:46 +1100, Matthew Kirkcaldie
>> <Matthew.Kirkcaldie at removethis.newcastle.edu.au> wrote:
>> 
>> >In article <erk3uvs9tqjkgkg2fklq2o4fls4u05ne2s at 4ax.com>,
>> > r norman <rsn_ at _comcast.net> wrote:
>> >
>> >> Yes.  Even glutamate has both in the retina.  I misspoke
>> >> about "all" the known glutamate receptors.  Glutamate is
>> >> "ordinarily" excitatory in the CNS.
>> >
>> >What's the inhibitory glutamate receptor in the retina?
>> >
>> >While we're on the subject, it's worth remembering that GABA is 
>> >excitatory in the immature CNS.
>> >
>> 
>> The synapse from receptor to bipolar is supposed to be glutamatergic,
>> even though "on" and "off" bipolars have opposite responses.  Here is
>> a reference
>
>...
>[skip many]
>
>Thank you!  Sigh, more reading.
>
>For others following the discussion, the other incredible thing in the 
>retina is that signalling is done by switching OFF the stream of 
>transmitter coming from the rods and the cones.  So a detectable burst 
>of light produces a temporary stop in the outflow of glutamate, and this 
>pause in secretion is what we actually detect as the basis for visual 
>stimuli!
>
>Show you how quickly the glial cells scavenge the glutamate from the 
>cleft - and why vision is actually the slowest of the senses in terms of 
>the briefest detectable stimulus.
>

It is a good example of the fact that a "negative" signal is just as
good as a "positive" one in communicating information. Stopping doing
something or turning something off is just as important as starting or
turning something on.





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