Ion channel "quantization"
Richard.Vickery at unsw.edu.au
Wed Aug 14 20:20:47 EST 1996
radams2000 at aol.com (RAdams2000) wrote:
>I have read that at the dendrites of a neuron, the current flow into the
>neuron across the synaptic junction consists of some large number
>on ionic channels that are either completely open or completely closed.
>So it would seem that, according to how many channels are involved,
>the current flow into the soma is highly "quantized", meaning that only a
>finite number of possible currents can exist. Does this contribute to
>a fundemental noise mechanism in the process of neural firing? Can this
>noise mechanism be measured accurately? Is it modelled in any of the
>popular neural simulation packages??
We need to be very careful about terminology here. Although the contribution
of channels will be to quantize current flow, the concept of a quantum (lets
call it a packet) in neurophysiology is inextricably linked with a transmitter
vesicle and its postsynaptic effect. This level of quantization (release of x
vesicles from y active zones (synaptic release regions)) has been extensively
studied, and is still the subject of a lot of debate. Quantization by channel
current flow (lets call it micro-quanta) has also been examined, and figures
in the argument about whether the fairly constant size of a packet is due to
constant amounts of transmitter in vesicles or due to saturation of the
postsynaptic site so that all channels are opened.
At the level of a neuron, the micro-quantization is unlikely to be
significant, as the varying distance of synapses from the soma will produce a
smearing of micro-quantal size, which makes it unclear whether even packets
can be reliably observed under normal conditions.
This reference might get you started:
Faber DS. Young WS. Legendre P. Korn H.
Intrinsic quantal variability due to stochastic properties of
Science. 258(5087):1494-8, 1992 Nov 27.
Richard Vickery \ / Our quest is for Meaning,
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