Sensory neurones - firing

[LARS THOMSEN]

To : All

First of all I would like to thank you all who answered my
first question about examples of sensory neurones who have 
cell body located close to the stimulus ?

The answers were as follows :

PHOTORECEPTORS, COCHLEAR HAIR CELL, STRECH RECEPTORS, OLFACTORY 
RECEPTORS, GUASTATORY RECEPTORS.

I looked up the sensors and found that all of them responds in a linear 
fashion to a increase in stimulus. However, in the enteric nervous 
system several authors say that the AH neurones are the sensory 
neurones. The AH neurone is characterized by having a prolonged after-
hyperpolarization (>4 seconds) following an action potential, which is 
caused by opening of calcium activated potassium channels.

I have always wondered why a sensory neurone would behave with such a 
strange pattern. The neurone is complete inactive during the after-
hyperpolarization, so it is not really a matter of adaptation, but more 
a question of making the neurone completely inactive. The AH neurones 
are possibly coupled to a regulation of physiological processes which 
need to spread in one direction (e.g. peristaltic movements). 

The reason why I asked about the location of the cell body is that in 
the guinea-pig the AH neurones or as people call them "the sensory 
neurones of the mucosa" are located in the myenteric plexus, which is a 
relatively long distance from the place of stimulus. 

I am currently working on a paper with a description of these neurones 
in the pig, which has a completely different arrangement than rodents 
(e.g. guinea-pig, rat, mouse). The results that we have found strongly 
indicates a additional or even another role for the AH neurones than as 
sensory neurones.

My last question is if anybody knows the existence of sensory neurones 
with a nonlinear correlation between impulse and firing ? I am aware of
different forms of adaptation. Any comments would be appreciated.
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