Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: eastbourne on 03/12/2010 17:29:50

Title: What is the role of calcium in muscle contraction?
Post by: eastbourne on 03/12/2010 17:29:50: Hi everyone,

After attending one of my tutorials at Uni this question bothered me and my lecturer wasn't able to answer it ... It relates to the role of Calcium in muscle contraction/ relaxation.

The release of Ca2+, after receiving the nerve impulse, liberates the myosin's binding site on actin filaments. This enables a contraction, and a return of the calcium in the sarcoplasmic reticulum allows the muscle to relax.
More to the point I also read that calcium is a factor that can cause cramp.
How can calcium have a relaxing and contracting effect on the muscle ?. Is there a link between this two processes or not ?

Could you help me please ! [O8)]

Thank you
Title: Re: What is the role of calcium in muscle contraction?
Post by: SteveFish on 03/12/2010 21:11:28: I am not quite sure what you are asking. Calcium ions are an intracellular signaling molecule for muscle contraction (and a large number of processes in other cell types). A neural synapse induces an action potential in a muscle cell (fiber) that, in turn, results in calcium ions to be released into the cytosol from the sarcoplasmic reticulum (excitation-contraction coupling) when calcium channels open. Calcium binds to troponin-C to initiate contraction and this will continue until excitation ceases and the molecular calcium pumps in the sarcoplasmic reticulum membrane remove and sequester the calcium. So the presence of intracellular calcium causes contraction, and its removal allows the muscle to relax.

Skeletal muscle cramps have quite a large number of causes, but some of them involve a condition that causes the sarcoplasmic reticulum calcium pump to malfunction so calcium can't be removed.
Title: Re: What is the role of calcium in muscle contraction?
Post by: eastbourne on 04/12/2010 15:49:11: Hi Steve,

First thank you for replying and helping me.
Yes I just realised I hadn't been very clear in my question.
I heard that alack of calcium can cause cramp (Of course there is other reasons why cramp occurs). But a drop in level of calcium inside the muscle fibers makes the muscle relax, because like you said the calcium pump brings the calcium back into the sarcoplasmic reticulum. So do you know why that is ?

The malfunction of the calcium pump explains it well.
Hope I made myself more clear for you.

Ps: I've found a website that quotes:
"Calcium deficiency: Muscle spasms can be due to lack of calcium in your food or malabsorption of calcium as calcium is vital in relaxing muscles"
http://ayurvedhealthcare.com/muscle-cramps.html

[O8)]
Title: Re: What is the role of calcium in muscle contraction?
Post by: SteveFish on 04/12/2010 21:47:59: Eastbourne:

I am at a loss on how low systemic calcium could cause tetany in a skeletal muscle cell. Tetany is continuous contraction and is the usual cause of cramping. I no longer have access to a biomedical sciences library or to one of my buddies who was a muscle research scientist, and my home basic science textbook library and a quick web search didn't help. If you find an answer to this, please post it. I do know quite a bit about the mechanisms of normal muscle contraction.

Steve
Title: Re: What is the role of calcium in muscle contraction?
Post by: eastbourne on 05/12/2010 11:59:28: Hi Steve,

Thank you very much for trying anyway I appreciate ! :)
On this website I've found why the calcium levels can drop:
http://www.cushings-help.com/calcium.htm
But there is no mention of the physiological disfunction. Unfortunately ...
If you get any new info on this could you let me know please too ! Cheers.