End Bulbs of Held

HARRY R. ERWIN herwin at osf1.gmu.edu
Wed Jul 2 15:07:33 EST 1997

I've been using GENESIS to model the circuit from the inner hair cell to
the bushy cells of the AVCN. It's been a bit weird, since it's hard to get
results matching those seen experimentally without playing around a lot
with the channels. In fact, it's hard to get matching results, even if I
play around a lot with the channels. The synaptic connection between the
type I ganglion cell and the bushy cell--the well-known 'End Bulb of
Held'--is even more interesting than I expected. It consists of a complex
of excitatory synapses wrapped around the soma of the bushy cell and is
believed to be constructed that way to ensure reliable transmission of the
action potential with minimum temporal dispersion. Not quite that simple.
Consider what actually happens--the effect of the afferent action
potential is to maintain the activation of receptor channels on the soma
for several milliseconds _after_ the bushy cell responds with its first
action potential. You don't get recovery--the K+ channels haven't got a
chance--but you don't get additional action potentials either. The soma
seems to just hang there at about 0 MV for an extended period until the
receptor channels shut down and then it might spike for a while. This
suggests bushy cells might be acoustic edge-detectors. Has anyone else
seen this?  Is my model out in left field?

Harry Erwin, Internet: herwin at gmu.edu, 
Web Page: http://osf1.gmu.edu/~herwin 
PhD student in computational neuroscience (how bats echolocate)
Lecturer for CS 211 (data structures and advanced C++)
Senior Software Analyst supporting the FAA

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