Basic question about neurons

Theophilus Samuels theophilus.samuels at btinternet.com
Sun Nov 25 08:03:20 EST 2001


  The question you ask is interesting. Physically speaking, neuronal input
far exceeds its output (i.e. number of dendrites (+ other axons synapsing on
the neuron) >>> single axon). However, looking a little deeper, this is not
entirely the case when considering input and output with respect to the
number of electrical signals recieved and transmitted per unit time.
  Dendrites are almost never myelinated, and they respond with graded
depolarisation or hyperpolarisation that decrements spatially and temporally
(some may actually generate action potentials). Firstly, if we consider the
time it takes for an AP to fire and the refractory period (say 5-10 ms) then
theoretically the output (electrical signals or action potentials) of an
axon ranges in the hundreds per second. Alright, considering that the number
of synaptic inputs to a single axon can range into the 100,000s, the output
number is still relatively small (although it is still 100 times more than
you might have first expected). Secondly, even though it is highly
debatable, as the AP is an all-or-nothing response, one might argue that
they are all that matters since they're the absolute and final product of
the culminated input signals. An analogy would be as follows: consider an
election process. Many thousands of individuals will vote for a single
candidate to win and represent the majority. It is this individual that
represents the collective voice of the many and is therefore the most
important consequence of the entire original electorial process. It is this
person that is the first representative met by other elected persons and
influences other decisions. So, if we now revert back to the neuron, we can
see that the really important consequence of all input signals is the final
action potential. And therefore, even though we might think that the output
profile of a neuron is severely limited, in reality it must be adequate
(perhaps even more than adequate!), otherwise we wouldn't be here to ask
such questions.

T.L.S.

chris ackerman <cma1114 at home.com> wrote in message
news:lumL7.44668$Ze5.25808688 at news1.rdc1.md.home.com...
> I am a neophyte so forgive the simpleness of my question, but why is it
that
> I always read descriptions and see pictures of neurons as having many
> dendrites and few axon terminals? If this is representative of most
neurons
> in the brain, how is it possible to have so many inputs and so few
outputs?
>
> Thanks,
> Chris
>
>





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