On Sat, 17 Apr 1999, Jennifer Trich Kremer wrote:
> Tipsters,
>
> I had a student ask the following question:
> "Since the nerve is made up of Na and K, if your diet is lacking in these
> substances will it affect your neurons??"
>
> I know that I could just answer yes, but I would also like to give some
> examples of what happens.
>
> Since this is not my speciality I am looking for some assistance!
I understand that it's extremely difficult for a normal individual to
become deficient by diet alone, as sodium and potassium are found
everywhere, and the kidneys are very efficient in retaining these ions
when they become scarce. I recall some old experiments where they
produced sodium deficiency by having volunteers living on a low-sodium
diet, but it took a long time before they developed a deficiency. For
what it's worth, the primary effect was a disagreeable loss of ability
to taste, and thirst. Curiously, water didn't help quench their
thirst, which required salt as well. The explanation now is that the
thirst was caused by loss of fluid from the extracellular fluid
compartment, which is not replenished by water. These observations, in
fact, led to the development of the current "double-depletion
hypothesis" of thirst. However, while neither sodium nor potassium
deficiency is likely to result simply from a poor diet, I believe that
factors such as diarrhoea, vomiting, certain drugs, and some metabolic
disorders may produce serious imbalances in these ions.
Potassium and sodium are not only important for neurons, but also for
maintaining the proper distribution of fluid in the intracellular and
extracellular compartments of all cells. Hyponatremia (low sodium)
causes water to shift into cells, overhydrating them. This causes
the brain to swell. A consequence is a seizure, which may due to brain
swelling but perhaps also to a direct effect on neuron functioning.
I would expect that hypokalemia (low potassium) has the opposite
effect, and produce cellular dehydration. A quick web check says that
its primary effect is on the heart, producing lethal arhythmia. It
also causes muscle weakness and paralysis of the respiratory muscles.
These sound like direct effects on nerve and muscle functioning rather
than due to dehydration.
Neurophysiologists are always fooling around with ionic concentrations
in studying nerve function. Perhaps someone else on this list can
provide us with details about what it does to nerve functioning.
Brief correction: My last post referred to "discrepency". Make that
"discrepancy". This is one word I should never write without first
checking a dictionary. The other is "diarrhoea".
-Stephen
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Stephen Black, Ph.D. tel: (819) 822-9600 ext 2470
Department of Psychology fax: (819) 822-9661
Bishop's University e-mail: [EMAIL PROTECTED]
Lennoxville, QC
J1M 1Z7
Canada Department web page at http://www.ubishops.ca/ccc/div/soc/psy
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