Hyperpolarization of Neurons

William Calvin wcalvin at u.washington.edu
Thu Apr 28 18:35:21 EST 1994


Mdh at debug.cuc.ab.ca (Mike Hamilton) writes:

>	I am curious, I have been reading about the GABA inhibitory 
>neurotransmitter, and how the sedatives such as alcohol and barbiturates 
>are attributed to their actions on these receptors. The reasoning behind 
>it is that a barbiturate would attach to the receptor would would result 
>in the opening of a chloride channel, which in turn results in the 
>hyperpolarization of the neuro and thus sedation? Could someone explain 
>why this hyperpolarization of the neuro would result in sedation? From 
>what I understand, the average potential across a neuron is approx. 90mV, 
>so why would increasing this sedate a person?

A typical resting potential might be -70mv and the threshold for firing
up around -60, i.e., 10mv positive to rest.  Any input that shifts the 
other direction "subtracts" from excitatory inputs and makes the cell 
less likely to fire.

Were this to happen in a widespread way (as from systemic drugs), a lot 
fewer cortical neurons would be firing (in the usual manner, though the 
number of spindles might increase).  That makes movement less likely, and 
probably thought as well.

If the drug affects one of the amine systems (those lawn-sprinkler-like 
systems from the brainstem and basal forebrain that affect excitability 
in many places at once), whole areas of cerebral cortex would be idling.
There's more in chapter six of Calvin & Ojemann, CONVERSATIONS WITH 
NEIL'S BRAIN, just out from Addison-Wesley.
    William H. Calvin   WCalvin at U.Washington.edu
    University of Washington  NJ-15
    Seattle, Washington 98195 FAX:1-206-720-1989




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