Ridecamp: Re: [RC] Lisa's comments on thumps

Heidi--

Thank you for the additions...as usual, I end up learning something when I
"teach", which suits me just fine. The day I stop learning is the day I'll
probably just park my butt in a rocking chair on the front porch.  From your
info, it appears that it is indeed a DCAD issue.


I was looking at the issue purely from the calcium angle, since the original
question dealt with calcium from LyteNow versus calcium from alfalfa being
stored.  This still holds true--but as Heidi points out, there is a lot more
to muscle contraction than simply calcium levels. In an effort to try
(somewhat successfully) to keep things simple, I left out info that probably
shouldn't have been left out.  Truman sent me a message reminding me of the
fact that horses are also in a state of alkalosis at the end of a ride--not
surprising, since because of the loss of so many positive ions from the body
via sweat and because of lack of oxygen.

You've also cleared up something else that bugged me--I was always taught
that the myelin sheath also made a nerve fire faster because the "charge" or
"impulse" traveled faster when it didn't have to hit every spot on an
exposed nerve membrane, it only hits the "nodes" between the myelin cells.
What baffled me was how this fit in with the fact that ions were inside the
neuron but the myelin sheath was outside.  Your explanation makes more sense
to me.

Moral of the story--no single electrolyte is going to solve any of these
problems.  They all are interconnected in their functions.  The way we
figure out how is by examining them one at a time.

Lisa

----- Original Message -----
From: "Heidi Smith" <heidi@xxxxxxxxxxxxxxx>
To: <greenall@xxxxxxxxxxxxx>; <ridecamp@xxxxxxxxxxxxx>
Sent: Wednesday, June 19, 2002 3:16 PM
Subject: Re: [RC] Lisa's comments on thumps


> > So what you are saying is that any muscle, the large hind end
> > ones in cows, and probably horses too, can lose Ca+ but for some
> > reason, certain horses lose Ca+ in the diaphram causing thumps.
> > Why the diaphram remains a question.  Perhaps there is a genetic
> > predisposition.  Perhaps that is why certain horses, getting what
> > would be considered adequate electrolytes, still thump.
>
> I agree that there is a genetic predisposition to thumping.  And to back
up
> a bit, no, thumps is not about calcium and muscle contraction--it is about
> multiple e-lytes and leakiness of the membrane of the phrenic nerve.
Where
> the calcium depletion comes in (per Lisa's post) is that calcium has been
> consumed during work by repeated muscle contraction, so that the ionized
> calcium may be low in circulation.  Hence, the whole e-lyte balance is out
> of whack.  (Along with e-lytes lost in sweat, etc.)  What happens in
thumps
> is that the phrenic nerve anatomically crosses the heart.  The heart has
an
> electrical discharge with each contraction, which is accomplished in a
> rather complex manner by electrolytes being rapidly transported across
cell
> membranes to produce an electric potential, and then being scavanged back
> across to end the "shock" so to speak.  The myelin sheath on the phrenic
> nerve is the "insulation" that protects the nerve from "firing" every time
> this discharge takes place in the heart--just like the coating around an
> electrical wire.  With an imbalance in e-lytes, this myelin sheath ceases
to
> do its job properly, so the "firing" of the heart in turn causes e-lytes
to
> "leak" into the phrenic nerve, causing it to "fire" as well.  Hence, since
> it services the diaphragm, the diaphragm in turn contracts every time the
> heart beats.  What I think is genetic is the intolerance of the phrenic
> nerve's myelin sheath to variations in the e-lyte "milieu" to which it is
> subjected--some horses seem to have a much greater sensitivity to even the
> slightest variation, while others would be long dead of outrageous
imbalance
> s long before their phrenic nerve's myelin sheath becomes "leaky."
>
> Can these horses be managed?  Sure, in all but the most serious ones, by
> carefully micromanaging their e-lytes.  Is this something that can be
> avoided by horse selection?  To a reasonable extent, yes.
>
> Heidi
>
>
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 Ridecamp is a service of Endurance Net, http://www.endurance.net.
 Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp
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