Talk:Muscle contraction

I have to complain about this page. "Twitching" or "twitch" redirect here but there's nothing on this page about twitching. This is unacceptable as many people use Wikipedia as a source of medical information.--Ensrifraff 06:33, 25 July 2006 (UTC)

Try the first sentence: A muscle contraction (also known as a muscle twitch or simply twitch) occurs when a muscle cell (called a muscle fiber) shortens. Raul654 06:47, 25 July 2006 (UTC)

That's a good clinical definition but if the word "twitching" is set to redirect here then this page would need a more comprehensive description of twitching. I must re-iterate that many people use Wikipedia for medical information and twitching is often a sign of more serious problems.--Ensrifraff 09:16, 25 July 2006 (UTC)

I just took my final in Anatomy and Physiology I. We had to answer a ten point question on muscle contraction, including action potentials, events at the neuromuscular junction, and the sliding filament theory. This article sums up nicely what we had to learn for the test. I planned on adding my own information to this page, but once I read through it I realized no editing was needed. Good stuff! Reynoldsrapture 22:26, July 29, 2005 (UTC)

Good work. Isotonic, isometric, concentric, eccentric contraction should also be explained. --Eleassar my talk 15:04, 26 August 2005 (UTC

I think the last paragraph is slightly misleading as it explains that calcium ions leave troponin after explaining smooth muscle contraction. Since there is no troponin in smooth muscle, I think this paragraph should be placed under the heading of "Skeletal muscle contraction".

I just quickly added that a reflex isn't always unexpected. Locmotion, eating, breathing etc.. all have a reflex aspect to them. I am not a writer though, so if someone can say it more elequently I would appreciate it. I also changed a few thing about action potentials. Please make more clear if possible. Thanks.

-Ryan

Need More and Corrections

I would be nice to discriminate between cardiac and skeletal muscle (Slow and Fast fibres), and mention the elastic protein titin in the organization (differences in titin are responsible for differences in stiffnes of cardiac and skeletal muscle). Difference in protein isoforms of myosin and actin, etc. Also a section on nonmuscle contraction apparatus and invertebrate striated muscle contraction is warranted. Maybe the flight muscles of flies would be good. GetAgrippa 17:24, 5 October 2006 (UTC)

There is an article on neuromuscular junction that should be incorporated into article. Further, the list of contraction is in need of correction. The last part about contraction is relevant, but the action potential I would assume has an article. There is a lot of neuroanatomy that could be included (distinct spinal cord pathways)if one is going to mention the brain to muscle need better description. Part is confusing. I would recommend just going from motor neuron to muscle and reference neuromuscular junction article and action potential article. Types of contractions like eccentric, concentric, and types of muscle fibers, oxidative metabolism , contractile protein isoforms, etc. should be mentioned. A better description of calcium metabolism is warranted or is there an article?

"The calcium causes the neurotransmitter, acetylcholine vesicles in the axon to fuse with the membrane, releasing the acetylcholine into the synapse between the axon and the motor end plate of the muscle fibre through the T tube system." This doesn't make sense and poorly worded. GetAgrippa 19:15, 10 October 2006 (UTC)

Perhaps a section on costameres and how the force is transduced from actin and myosin to sarcolemma to tendons, and how a muscle can generate isometric and isotonic force and how does it do it. GetAgrippa 23:32, 11 October 2006 (UTC)

ATP hydrolysis

This article makes it seem as though 2 molecules of ATP are required for one full cycle. This is not the case. Also, the power stroke of the myosin/actin complex is not a result of hydrolysis of an ATP molecule by the myosin ATPase but rather the release of ADP from the myosin/actin complex. The steps are as follows: Conditions at beginning of cycle: 1 ATP molecule present and the myosin head is complexed with the actin molecule. Step 1: ATP binds to the ATPase site of the myosin head causing the myosin/actin complex to fall apart. Step 2: ATP is hydrolyzed and the myosin filament takes on the "cocked" position. The inorganic phosphate is released but the ADP molecule remains attached to the myosin head as the myosin binds to an actin protomer closer to the z line than the previous myosin-binding site (majority of molecules during a concentric contraction). Step 3: The ADP molecule is released and the energy from the release causes the power stroke, moving the myosin and actin filaments past eachother. Step 4: The myosin head remains complexed with the actin molecule until another ATP molecule binds to the myosin head and frees it from the actin myosin-binding site. 128.104.105.100 19:34, 21 September 2006 (UTC)

Illustrations

It would be nice to have some illustrations of the contractile apparatus and contraction. Demonstrate the movement of tropomyosin to open active actin sites for myosin interaction, calcium release from SR, Myosin cross-bridge and the 10 nanometer ratchet along actin,etc.A picture is worth a thousand words and there are a huge number of illustrations available. GetAgrippa 17:14, 5 October 2006 (UTC)

Thank you WLU for adding the sarcomere illustration. Excellent addition.GetAgrippa 17:37, 16 December 2006 (UTC)

Smooth muscle

I rewrote the smooth muscle section. I can provide references, but most is considered fairly common knowledge. I wrote it quickly so it may need some editing. GetAgrippa 17:24, 5 October 2006 (UTC)

New Sections?

This page is getting quite full and has a lot of great information. I remember seeing this page a few years ago and it didn't have 1/8 of the stuff. The writeups on striated and smooth muscle have so much info, I wonder if they should be their own page. A highschool student wanting to know the difference may be overwhelmed with the level of explanation which is at or above the graduate level. I wonder if we should have a briefer explanation highlighting the differences (ryanodine recepter types, striation, mechanism: ca2* vs MLCK) and have the very detailed stuff on their own page.

Also, there is no section for cardiac. I wonder if the "skeletal" part should be labled striated and anything prior to calcium release in the SR stay there. Above that, or below, have the differences in the induction of contraction in both skeletal and cardiac since that is the main differences. Just a few ideas. I wouldn't mind helping if others agree. Rjkd12 15:06, 1 December 2006 (UTC)

I like adding the Cardiac section differences in histology, contractile protein isoforms, titin isoforms, contractile properties and physiology, etc. GetAgrippa 22:48, 23 February 2007 (UTC)

Reference

I re-added the Brooks reference at the bottom - when I wrote the eccentric and concentric muscle contractions sections I used Brooks as my basic guide. It's a textbook of exercise physiology so it does provide information relevant to the entire article. It's not tied to specific sections or statements because it was used generally throughout.

I had thought I read somewhere that this was allowed (i.e. not everything has to be a numerated foot-note), but can't find it with a quick search. If anyone wants to take it out again I won't re-add unless I can find the relevant policy. WLU 20:54, 23 February 2007 (UTC)

For short articles, it's not a big deal, but for long articles, having a book listed at in the references section without tying it to any specific assertion can give a false sense of security to the reader, and make it harder to maintain the articles in the long run. (For example, certain sections of the article will probably need to be split out at some point into new articles. If the references aren't tied to the text, we won't where the reference should be listed.) It is true that this didn't use to be such a big deal, but since Wikipedia:External peer review/Nature December 2005/Errors, there seems to be a much greater emphasis on explaining where our facts come from, especially in the sciences. If you want the reference in, I won't take it out, but I think it would make the article much stronger if we could tie actual page numbers to actual statements in the wikipedia article. Do you still have the book? --Arcadian 00:14, 24 February 2007 (UTC)

I do and I still use it, it's a good book. It'd be a lot of work to go through for points and match up. I'll try reading through and if anything I remember came specifically from the book I'll try throwing in a reference. It may take me a while though. If there's anything you see as needing a reference, point it out and I'll try to find it. Right now I'm playing catch-up on my watchlist but I'll try to get to it in the future. WLU 19:52, 24 February 2007 (UTC)

Eccentric

"the muscle lengthens as it contracts." Does this make sense? Could it be explained better? Xxanthippe 10:46, 18 April 2007 (UTC)

It's the exact definition of a muscle contraction - the joint opens and the muscle lengthens despite the action of the contractile proteins. Muscle contraction is the statement used to describe the contractile proteins working. I suppose you could replace "contracts" with some reference to the muscle trying to shorten. It seems counterintuitive, but the meaning of 'contract' in the sentence is a specialized scientific/physiological one rather than the general 'becomes smaller' meaning. WLU 12:35, 18 April 2007 (UTC)

The standard linguistic meaning of contract is "gets shorter" i.e. reduces in length. Is standard linguistic usage more appropriate to an encyclopedia than counterintuitive medical terminology? Is it the case that Concentric Contraction means that the muscle contracts while under the influence of the load (the applied force) and Eccentric Contraction mean the muscle expands while under the load? Xxanthippe 11:51, 19 April 2007 (UTC)

Since this is an article about muscles, using terminology specific to muscle may be appropriate. I'll try a clearer definition.

Muscular contraction as a whole is not about the muscle shortening or lengthening, it is about the acto-myo fibers working. The two types of contractions refer to whether the muscle lengthens or shortens while working. In each case there are filaments sliding across each other, trying to shorten the muscle, it is a matter of if they are successful or not. WLU 14:43, 19 April 2007 (UTC)

I edited some of the eccentric stuff. Eccentric work isn't "not normal" or strange any more than concentric work. Muscles don't "normally" close a joint either, so eccentric work doesn't normally open one. Muscles aren't "supposed" to contract concentrically. Also, nobody knows what happens to the myosin heads during eccentric work. What they do during concentric work isn't well known either. Now there is the latch theory where the myosin head rotates at the myosin-actin interface instead of near the "hinge" region. By rotating at the myosin-actin interface it extends an extensible region in the neck (like a spring) and then contraction occurs when the spring pulls the head in. Rjkd12 18:24, 18 May 2007 (UTC)

For an eccentric contraction to occur, the force acting on the muscle must be greater than the force the muscle is producing. I'm not saying its more than the maximal force the muscle can produce, just more than its producing at that point. I agree "contraction" may not be the correct word. To contract means to shorten, and the muscle isn't shortening. I think "activated" is a better word because lengthening during activation is much different than lengthening while the muscle is relaxed. But, we should still use the term "contraction" because its still an "eccentric contraction." Remember, there are three types of contraction, eccentric, concentric, and isometric. Its an archaic term.Rjkd12 14:50, 22 May 2007 (UTC)

Removed link

The following link from the EL section has disappeared. Anyone know why?

• {{McGrawHillAnimation|physiology|Action%20Potentials%20and%20Muscle%20Contraction}} WLU 01:09, 22 May 2007 (UTC)