IUBio

minds and brains

Walter Eric Johnson wej3715 at fox.tamu.edu
Mon Jan 4 19:34:30 EST 1999


Dirk Wessels (icircle at xs4all.nl) wrote:
: Eugene Leitl wrote:
: 
: > This is off-topic for bionet.neuroscience, but there are things like
: > true randomness (from quantum noise) and then there is nonpredictable
: > determinism.
: 
: It is not off-topic, if you include "micro-tubes" (or what were they
: called again,those bundled small atomic sized tubes of carbon).

microtubules?

: These are supposed to be inside every cell of the body,
: and appear very frequent in neurons.

At least those with axons.  Are they also present in neurons 
that don't have axons?

: Besides that the little tubes
: called
: DNA-molecules are also small enough.

There are many objects and bodies in a neuron that are very small.
The bigger question is whether these bodies are small enough that
the quantum effects are significant.  Microtubules are about
20-26 nm in diameter (Pannese, Ennio, Neurocytology).  At
what scale would the quantum effects become significant?
 
: The quantum states of many of these tubes may work together, and
: increase the area that depends on "quantum randomness".

Are you saying that this "quantum randomness" has an effect on the
conduction of an impulse along the neuron?  There is at least
one obvious problem with that view.  The impulse is conducted
along the cellular membrane of the axon.  IIRC, experiments have
shown that there is little difference between the potential
conducted along an intact axon and an axon with the contents
removed.  Thus, it is difficult (at least for me) to see
how quantum effects on microtubules or DNA would have any
measureable effect on the transmission of the impulse along
the axon.

I'd expect more of a possibility of an effect at the synapse,
in the diffusion of neurotransmitters across the synaptic
cleft, and in the electrotonic transmission across gap
junctions.  But I could easily be wrong about that.

: Especially if they have the same direction and form.
: It is then more likely that "the quantumstate" will then be shared
: among the many tubes.
: 
: But then again, it is not "nice" to talk about quantum-effects in
: this newsgroup, because almost no neuro-scientist will be able
: to understand what kind of effects this may have.

There are some around.  I know of one from more of the computational
side with degrees in physics from Harvard, Cambridge, and MIT.

Eric Johnson



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