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Neuron transmission speeds, relative to size

Xuguang Liu xl at physiol.ox.ac.uk
Wed Jul 10 04:28:48 EST 1996


On 9 Jul 1996, Bill Skaggs wrote:

> Date: 09 JUL 1996 16:41:51 -0700 
> From: Bill Skaggs <bill at nsma.arizona.edu>
> Newgroups: bionet.neuroscience
> Subject: Re: Neuron transmission speeds, relative to size 
> 
> david at monteith.win-uk.net (David Monteith-Hodge) writes:
>    > During my research I cam upon an article which stated "larger
>    > brain cells conduct impulses faster than smaller ones".
>    >
>    > I would not know where to start to discover the truth of this
>    > statement, but need to know something about it as it determines
>    > whether I design and build a large sequence of experiments. Would
>    > one of you erudite folk be able to throw some light onto this for
>    > me? You would make a mature student ver happy. 
> 
> On the whole, neurons with thicker axons conduct impulses faster,
> because their resistance per unit length is lower.  Thicker axons
> impose greater metabolic demands, requiring more metabolic machinery,
> some of which is localized to the cell body.  Therefore fast-
> conducting neurons tend to have large cell bodies.  There is not,
> however, any direct causal relationship between cell size and
> conduction velocity.
> 
> 	-- Bill
> 

The velocity of saltatory conduction along the myelinated nerve fibres is 
proportional to the outside diameter of the nerve, in which a thick 
myelin improves electrical insulation and hence reduces internodal losses of 
current across the cell membrane and thick axis cylinder reduces core 
resistance and thus improves the longitudinal spread of current. 

Xuguang



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