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Enough physics, how about physiology....(9 posts)

Enough physics, how about physiology....Wayne
Oct 17, 2002 12:22 PM
why do bodies get stiff (rigor mortis) when a person dies?
According to Websters. . .czardonic
Oct 17, 2002 12:27 PM
"It is due to the formation of myosin by the coagulation of the contents of the individual muscle fibers."

I take that to mean that a chemical change occurs in the muscles that eliminates their flexibility.
Oct 17, 2002 12:50 PM
this is from a website that I found and from my recollection of studying this stuff the info below seems correct. It's actually similar to tetany (tetanus or twitch) where the ATP is locked and cannot/doesn't release but eventually the bound ATP breaks down and the body goes limp again.

Explaining the development of rigor is a serious undertaking, because first you must understand the biochemistry of muscle contraction. Fortunately, for our purposes, we can make some grand simplifications. When the myosin molecules of the thick filaments are "grabbing and swivelling" their way along the thin filaments, causing the filaments to slide past each other for muscle contraction, they require a constant stream of energy from ATP. Before a myosin molecule of a thick filaments can release itself from an actin molecule of the thin filament, it requires some new ATP. Without ATP, myosin stays locked onto actin, even if the muscle is trying to relax. Thus, when living muscle finally runs out of ATP after rigor mortis develops.
Ohhhhh. This explains post-mortem muscle contractionsKristin
Oct 18, 2002 5:47 AM
Or the "jerks" as some people call it. Freakiest think in the world. I worked for a vet when I was 16 and was involved in many euthanasia's.
Different phenomena...Wayne
Oct 18, 2002 5:58 AM
see my post below. I think post-mortem muscle contractions would be explained by areas of the brain or peripheral reflexes firing and stimulating muscle contractions which is different then the whole body getting stiff (rigor mortis). It seems to me it would take a few minutes for the brain to "die" once the heart stops beating or the animal stops breathing. Or even think about a chicken with it's head cut off, the "system" is still capable of generating coordinated muscle contractions for a few seconds (minutes?) until the spinal cord "dies".
Alright now the big question: Post mortem erections!Sintesi
Oct 18, 2002 7:04 AM
True, not true? Wives tale? And why would wives be telling this?
Oct 18, 2002 6:11 AM
Some day...I'll tell you my stories of the many hours I "served" in the morgue doing autopsies for our hospital and the coroner.

Hey, I was broke. I was in med school. They paid me a lot (they would have to). It wasn't much different than gross anatomy lab, except for....oh nevermind.

Those muscle twitches scared the sh*t out of me every single time.
Ugh, I imagineKristin
Oct 18, 2002 6:29 AM
There's a big difference between Fluffy twitching away as I stuffed him into a garbage bag and a no-longer-living human twitching. I don't think I could have handled a real morgue job. *shivers* Never look into the eyes.
The answer...Wayne
Oct 18, 2002 5:34 AM
is largely covered in the above post. The way your muscles contract is via the release of Calcium ions that activate the contractile machinery (actin and myosin). When you die calcium leaks out of it's holding area (a passive process) and is not re-sequestered there because this is an energy consuming process and you're not producing any new ATP. So progressively more calcium is released into the cell and the mysoin binds to the actin increasing the stiffness of the muscle. To unattach requires another ATP molecule to bind to the myosin head but there's none around. Thus the body gets stiff until the actual muscle contractile proteins start to decompose.