Talk:Muscle contraction

Multiple fiber summation

Article quote: "When a weak signal is sent by the CNS to contract a muscle, the smaller motor units, being more excitable than the larger ones, are stimulated first. As the strength of the signal increases, more motor units are excited in addition to larger ones".

I find the last sentence to be unclear. What does "when the strength of the signal increases" refer to? An increased frequency? Or amplitude? Or Number of firing neurons?

Can anybody help?

Newtons third law

I have a problem with statements such as: "In concentric contraction, muscle tension is sufficient to overcome the load, and the muscle shortens as it contracts.[8] This occurs when the force generated by the muscle exceeds the load opposing its contraction." Newton's third law requires that the muscle tension and its load, possibly including inertial loads, be equal. It is the muscle ability to generate force while isometric that exceeds the load in a concentric contraction and is exceeded by it in an eccentric contraction. I am new here so reluctant to just change it. Advice appreciated. Thanks, David Morgan Drdrdlm (talk) 11:34, 31 July 2018 (UTC)

Thanks for your interest. If you're uncertain, a good first strep would be to rephrase that sentence and propose it as a substitute. Have source(s) ready (see WP:RS and WP:V). Other editors may provide additional input. If no one objects, then be bold (see WP:BOLD) and make the appropriate changes. Hope this helps. danielkueh (talk) 11:52, 31 July 2018 (UTC)

Hi David, I think you and I have similar concerns. If I am understanding the terms correctly, I am not seeing a problem with the example you cite because when you say, "Newton's third law requires that the muscle tension and its load, possibly including inertial loads, be equal," I think that is by definition only true in an isometric situation. As soon as the muscle tension is greater than the load, the load will accelerate and the muscle will shorten, so the contraction is by definition concentric. Please correct me if I am wrong.

But, along those lines, I have a problem with this paragraph:

"Though the muscle is doing a negative amount of mechanical work, (work is being done on the muscle), chemical energy (originally of oxygen,[12] unlocked by fat or glucose, and temporarily stored in ATP) is nevertheless consumed, although less than would be consumed during a concentric contraction of the same force. For example, one expends more energy going up a flight of stairs than going down the same flight."

I am not convinced by the flight of stairs example that an eccentric contraction equal in force to a concentric contraction would consume less energy. Going up and down stairs requires such a complex interplay of muscles (and bone structure) that it feels impossible to isolate one muscle to compare the energy consumed when it is in concentric contraction versus eccentric contraction. Further, in any example involving the lifting or lowering of a load in a gravitational field, the force of the lowering, eccentric contraction must be less than the lifting, concentric contraction, so will of course require less energy.

A better example would be if a person were in space and a small asteroid were coming toward them. The person stretches out their arms to receive the astroid, and from the moment the asteroid touches their hands the person's triceps begin pushing against the asteroid and maintain a constant muscle tension as their arms first fold up to slow the asteroid then extend again to push the asteroid back.

The force exerted by the triceps, i.e. muscle tension, is constant through the eccentric contraction, the instantaneous isometric contraction, and then the concentric contraction. Would this then demonstrate that less energy was consumed during the eccentric contraction? I don't know, but my instincts tell me no since the triceps are exerting themselves at the same tension throughout.

My proposal, then, is to eliminate the words, "although less than would be consumed during a concentric contraction of the same force. For example, one expends more energy going up a flight of stairs than going down the same flight."

I won't do it, though, in case I am completely misunderstanding the whole thing. Let me know and thanks!

Ellis Ellisbaggs (talk) 19:21, 4 February 2022 (UTC)

Cardiac Muscle

What is the citation for the paper saying that the temporal summation of 30,000 Ca++ ions is what causes the intracellular calcium increase. Obviously more Ca would cause a higher concentration, but where does the number 30,000 come from

Pumwi23 (talk) 03:55, 10 October 2023 (UTC)

Wiki Education assignment: BYU-Biophysics, CELL 568

This article was the subject of a Wiki Education Foundation-supported course assignment, between 5 September 2023 and 14 December 2023. Further details are available on the course page. Student editor(s): Pumwi23 (article contribs). Peer reviewers: Smbiophysics, Jwiggler.

— Assignment last updated by Smbiophysics (talk) 16:40, 19 October 2023 (UTC)