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Action Potential / Contraction / Charlie Horse Pain

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dwijeshsheth

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Okay this has been confusing me sorry for this stupid question.

In order for the muscle to contract we have Ach coming from the neurotransmitter going in the T-Tubules making Ca+ leak out from SER. Leading to muscle contraction right?

So if a patient has a spasm / Charlie Horse pain wouldn't that be due to too much Ca+ rather than low Ca+? Since Ca+ is making it contract?

:confused:
 

Jamiu22

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Okay this has been confusing me sorry for this stupid question.

In order for the muscle to contract we have Ach coming from the neurotransmitter going in the T-Tubules making Ca+ leak out from SER. Leading to muscle contraction right?

So if a patient has a spasm / Charlie Horse pain wouldn't that be due to too much Ca+ rather than low Ca+? Since Ca+ is making it contract?

:confused:

You have to look at it as what's going on intracellularly vs. extracellularly... the condition you mentioned earlier w.r.t to contraction is calcium being released from the SR (intracellulary).. so you get contraction.

The Charlie Horse scenario you mentioned seems to be describing hypercalcemia, which is extra cellular calcium overload. If you have too much calcium on the outside of the cell... it will do the opposite effect as that with having too much calcium within the cell. That's why you get Tetany with hypocalcemia.

I used the same logic for K+ & Na+... I know what's happening inside the cell... I now flip it when I'm thinking of what's happening outside the cell (blood levels).
 

dwijeshsheth

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You have to look at it as what's going on intracellularly vs. extracellularly... the condition you mentioned earlier w.r.t to contraction is calcium being released from the SR (intracellulary).. so you get contraction.

The Charlie Horse scenario you mentioned seems to be describing hypercalcemia, which is extra cellular calcium overload. If you have too much calcium on the outside of the cell... it will do the opposite effect as that with having too much calcium within the cell. That's why you get Tetany with hypocalcemia.

I used the same logic for K+ & Na+... I know what's happening inside the cell... I now flip it when I'm thinking of what's happening outside the cell (blood levels).

What's confusing me is that I've read that it's caused by low Ca+ levels which is mentioning low Ca+ inside the cell rather outside the cell right?

Sorry!
 

Jamiu22

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What's confusing me is that I've read that it's caused by low Ca+ levels which is mentioning low Ca+ inside the cell rather outside the cell right?

Sorry!

I would have to look at what you are reading specifically... but you are correct in your initial assessment that low calcium inside a muscular cell would cause less contraction and a higher means more contraction.... and this is a fact that does not change. Low calcium levels inside a cell can not cause increased contractility. Drugs such as Digoxin take advantage of this physiology.

when you talk about low calcium causing increasing contraction... they can only mean outside the cell (hypocalcemia).
 

dwijeshsheth

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I would have to look at what you are reading specifically... but you are correct in your initial assessment that low calcium inside a muscular cell would cause less contraction and a higher means more contraction.... and this is a fact that does not change. Low calcium levels inside a cell can not cause increased contractility. Drugs such as Digoxin take advantage of this physiology.

when you talk about low calcium causing increasing contraction... they can only mean outside the cell (hypocalcemia).

Great! Thank you so much! Appreciate your help!

I can't find the article that I was reading earlier, but I checked out other website which pretty much summarizes our discussion.

This was driving me crazy!
 

calvnandhobbs68

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What's confusing me is that I've read that it's caused by low Ca+ levels which is mentioning low Ca+ inside the cell rather outside the cell right?

Sorry!

No what's happening with hypocalcemia and tetany is that low extracellular calcium increases the membrane permeability to Na+. When the Ca+ conc gets low enough, the neurons start spontaneously firing and cause tetany.
 

dwijeshsheth

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But wait isn't a Charlie horse basically a cramp? Isn't a cramp a powerful contraction?

So how can this be low Calcium levels inside the cell leading it to contract so powerfully?



(Nevermind it's high levels of Ca+ outside of the cell correct?)
 

calvnandhobbs68

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But wait isn't a Charlie horse basically a cramp? Isn't a cramp a powerful contraction?

So how can this be low Calcium levels inside the cell leading it to contract so powerfully?



(Nevermind it's high levels of Ca+ outside of the cell correct?)

Where are you finding that hypercalcemia (e.g. high levels of serum Ca+) are causing muscle cramps?

The reasoning behind tetany actually has nothing to do with the relative Ca+ concentrations inside and outside the cell. The Ca+ binds to Na+ channels on neuron membranes and decreases the excitability, so hypocalcemia (low serum calcium) would cause higher rates of spontaneous firing leading to prolonged contraction (cramps or tetany).

http://en.wikipedia.org/wiki/Hypocalcaemia#Symptoms
 
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