nerve message transmission. Help please.

Matt Jones jonesmat at ohsu.edu
Fri Oct 17 14:54:24 EST 1997


In article <623mof$rcm at gap.cco.caltech.edu> Hannah Dvorak-Carbone,
hdvorak at cns.caltech.edu writes:
> I have no idea
>what you mean by "levels" (levels of what?),

I think the original poster might have been asking about the magnitude of
the signal. So, to answer that in very approximate terms:

When the ACh receptors are activated, each one opens an ion channel. The
electrical units of this effect are therefore "conductance", and measured
in picosiemens (10^-12 siemens; 1 seimen = 1Amp/1Volt = 1/1Ohm). Under
the usual conditions, this is equivalent to a flow of current equal to
1-2 pA (1 pA = 10^-12 Amps), and/or a depolarization of a millivolt
(10^-3 V) or so. Since there are thousands of ACh receptors activated by
each action potential in the motor nerve axon, the muscle receives
nanoamps (10^-9 Amps) of depolarizing current, and is usually driven to
the spike (action potential) firing threshold. At the peak of the action
potential, the muscle membrane may reach a voltage ~150 millivolts
positive to its resting potential of around -90 millivolts (measured from
the inside of the cell relative to the potential of the extracellular
fluid). 

I suggest reading "Nerve, Muscle and Synapse" by Bernard Katz. He was a
Nobel prize winner, and one of the people responsible for the majority of
our understanding of neuromuscular transmission. It's a very readable
book, and you can finish it in a day. 

-Matt



More information about the Neur-sci mailing list