Basic Question

[COLLEEN M. SPECHT]

In article <53i9gk$ss5 at highway.leidenuniv.nl>, Schaap at rullf2.medfac.leidenuniv.nl (Jeroen Schaap) writes:
>In article <52ov40$4q2 at gap.cco.caltech.edu>,
>Maybe it is theoretically possible to take a segment of an axon an 
>determine which the direction is. But I am not mentioning any 
>electrophysiological properties. I am not very sure, but I believe the 
>cytoskeleton grows in one direction, with helices turning in a special 
>direction. Theoretically, I stress, it might be possible to determine 
>the direction of the cytoskeleton in an axon-segment and with that the 
>direction of the propagation of action potentials in 'normal' 
>situations. 

good point!

>	Second, I can also imagine  antidromic ap's could have an 
>influence on the membrane potential of the soma/ axon hillock by means 
>of electrotonic interaction. But results will be very difficult to 
>interpretate. Because the different potentials involved in an ap as a 
>function of time, there will be no simple elevation of depression of 
>membrane potential. I don't know whether some slow channels have been 
>proved on axons -please help me with this- but they could de- or 
>hyperpolarize the soma.

i don't think anyone would argue this point - and there is really no reason to
think that this couldn't take place.  however, sodium/potassium atp-ase used a
considerable amount of energy to prevent this from happening.  and even if a
tiny current did make it to the hillock (which i would think a tiny current
always does...) it in not enough to make an a.p.

>	Third, why couldn't any action potential be generated on an 
>axon, by means of axo-axonic synapses etc. Off course the axons don't 
>have the ap generating mechanism, axon hillock, but nevertheless, why 
>couldn't the 'axonic synapses' depolarize enough in order to generate an 
>action potential.

again, this would theoretically work, but has not yet been found.  there IS
such a thing as the axoaxonic synapse, which results in presynaptic inhibition. 
to generate an action potential you would need many many many such synapses on
a single axon i would think (this is what has not yet been found).

>Things are never that simple they seem to be.

>Jeroen

but jeroen, were they simple wouldn't they bore you?  

cheers,

colleen specht