Why do dead bugs and mice ‘stiffen up’ in specific positions where as other dead animals simply go limp?
In: Biology
I don’t know about bugs, but animals don’t go limp, I mean immediately after death they do, but within hours rigor mortis sets in. That’s because the SERCA pump required to sequester calcium in storage (terminal cisternae, sarcoplasmic reticulum) needs energy (ATP) to operate. No oxygen and metabolism upon death means no more ATP generated, so calcium starts to diffuse out of storage, go to the sarcomeres (force generating units), bind and shift proteins causing many cross bridge formations (tiny flexes) which slowly contracts the muscle. In order for the proteins in the sarcomeres to let go (myosin let go of actin) it also needs ATP, so you slowly flex more and more but you can’t relax, because that requires energy. So you get rigor mortis.
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