Problems with myelin theory

Jeremy Leipzig jeremyl at mindspring.com
Thu Feb 12 20:14:59 EST 1998


Several neuroscience textbooks cite the ability of myelin to increase
the capacitance of the neural membrane as one of its principal means of
increasing the velocity of propagation of neural impulses.  Increasing
the capacitance of the membrane (by effectively making it thicker) means
less charge is needed to create the same potential difference across
that membrane.

I am confused by this claim for the following reasons:
    1) There is no myelin in the Nodes of Ranvier where the
voltage-gated ion channels are located.
    2) Increasing the capacitance of a membrane would increase the
electric potential across that membrane but it would not increase the
electric field.  The same way, for instance, walking up a flight of
stairs increases your potential energy while your weight remains
conserved.
    Hence, the force exerted on ions would be the same regardless of the
presence of myelin.  As I remember, voltage-gated ion channels are
governed by the force exerted on charged amino acid helices that form
pores through which ions can travel.  These channels would only respond
to a change in the electric field, not merely electric potential.

Am I correct in my doubts?  Your thoughts would be greatly appreciated.

--
Jeremy Leipzig         http://www.mindspring.com/~jeremyl       
(919)469-0936
1204 Kilmory Dr. Cary, NC 27511                        
jeremyl at mindspring.com
 




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