kkollins at pop3.concentric.net wrote:
>jimmyd at cc.gatech.edu wrote:
> > * If neurons get all their energy from glucose, then what is the purpose of
> > oxygen in the brain?
>> The same purpose it serves in an automobile engine.
(this is over-simplified, but..) It is necessary to maintain normal metabolic
activity. Oxygen acts as a mitochondrial electron acceptor. Glucose is the
substrate. Also necessary, are adequeate numbers of mitochondria to produce the
energy.Without sufficient oxygen (or the ability to produce energy from it), anerobic
metabolism commences and its end products may be fatal to the cell.
> > * What happens if a neuron is heavily stimulated with messages from its
> > dendrites, but there is not enough energy in the local bloodstream to increase
> > the firing rate very much?
> kkollins wrote:
> If this condition occurred, neural activations states would tend to become random
> to the degree that it did, and the nervous system's information-processing
> capacities would be decreased accordingly. But the evolutionary engineer has
> handled this very circumstance nicely, and as any such condition shows itself,
> system reconfiguration mechanisms are activated, and the nervous system guides the
> effector activations of its host organism so that the organism will "move away
> from" what has become a noxious environmental circumstance.
IMHO, if the rate of firing of presynaptic pools exceeds the metabolic rate/capacity
of the postsynaptic pool, we have very characteristic, predictable changes (not
random). If these pools lack sufficient fuel and intracellular machinery to produce
ATP without anaerobic metabolic activities, they suffer (one example) failure of
ATP-dependent functions such as ionic pumping. This allows a build-up of Na+ in the
cell, or a shift towards the sodium equilibrium potential, and off we go. The same
fate also finds the neuron which suffers too little stimulation.
Because of the reticular and integrated nature of the neuraxis, decreased (or, loss
of) function of one pathway or neuronal pool will surely affect another. (i.e.
spreading depression, or transneuronal degeneration).
The human nervous system is sensory based and the ability to transduce environmental
information into action potentials dictates the state of integration of central
neuronal structures. Our ability to perceive our environment, to experience our
world, is dictated by the frequency of activation of peripheral receptors, and the
subsequent increased probability of summation of central post-synaptic pools.
*Attempting to be professionally _polite_ and accurate,