In article <Pine.3.89.9606101243.A7262-0100000 at lex.lccc.edu>, rcb1 at LEX.LCCC.EDU (Ron Blue) writes:
|> A quick question for those of you with expertise in neuropsychology. When I
|> was an undergrad (and grad student as well), I was taught that the threshold
|> for an action potential was close to -55 mv. This value also seems to be
|> backed up by the classic Scientific American article by Stevens (1976).
|> Although I realize there are no absolutes, I've been teaching my students to
|> use the value of -55mv as an approximate threshold value.
|>|> Interestingly, I've just switched to the Weiten text, and in one of his figures
|> the threshold value is shown as -40mV. I also had a student that had two
|> neurophysiology courses that stated she was taught the threshold was closer
|> to -40 than -55. I'd just like to be cleared up on this issue. Is there a
|> relatively well-accepted threshold value, and if so, what is it? TIA.
There is no one threshold value for the action potential. There are large
differences across species and different areas of the nervous system. The
threshold can even change over time in a single neuron; for example a cortical
neuron _in vivo_ may have a threshold around -45 mV, but when cut out as part of
a brain slice and recorded _in vitro_ its threshold may change to -60 mV. In
general neuronal thresholds are 5-10 mV above the resting potential of the
neuron, and because resting potentials can vary over a large range (~50 mV),
thresholds also vary.
Paul
