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Re: Twitching Muscles! [HAPP-L]



>Twitching muscles are typically due to one of three physiological 
>phenomena: (a) spontaneous release of Calcium from the SR, which 
>initiates excitation-contraction coupling in a few isolated skeletal 
>muscle cells; (b) spontaneous action potential in a motor neuron 
>innervating a few skeletal muscle cells (i.e. very small motor 
>unit); (c) spontaneous release of Ach from the motor neuron due to 
>calcium leak, thereby initiating excitation-contraction coupling in 
>a small motor unit.
>
>Bob
>--

Bob,

OK, and thank you, but...why? Why does it happen?

For instance, I have an eye muscle that "twitches" involuntarily from 
time to time...starts suddenly, stops suddenly...no special event 
attached to it...except maybe it occurs more often when I'm overly 
tired.
And, this student says she ahs a facial muscle that does the same 
thing, usually when she is upset or stressed.

So, why? Or how? What is the connection? Why does it happen to some 
people, at some times, and to some muscles? I need to be able to 
explain it it "lay" terms...for non-science majors. I understand the 
"mechanics," I just don't have an answer for the "Why?" for her. 
Anyone have any good methods for explaining this, or "get" what I'm 
asking/getting at?

Thanks!

Leslie Carlson
Dept. Zoology/Genetics
Iowa State university