The rigidity is caused by the binding of myosin to the actin fibers : After the onset of death, ATP is no longer regenerated from ADP . Ion pumps therefore stop working. Inside the muscle cells, the ion pumps keep the calcium concentration in the cytoplasm low. After death, calcium ions diffuse from the sarcoplasmic reticulum into the cytoplasm, which ultimately leads to the binding of the myosin to the actin filaments , as the calcium ions cancel out the isolating effect of the troponin . Due to the absence of ATP, the bond is no longer broken and the muscle solidifies (see contractile mechanism ).
In humans rigor mortis begins after about one to two hours at room temperature in the eyelids, chewing muscles (two to four hours) and small joints, then it sets in on the neck, neck and further down the body, and is fully developed after six to twelve hours ( faster in heat, slower in cold). However, this sequence, described by the Nysten rule , is only found in about 50 percent of cases.
It is more important that the individual fibers of a muscle solidify only gradually. If the rigidity of a muscle is broken by external movements before it is fully developed (i.e. within the first 14 to 18 hours), after a while a new rigidity sets in in this muscle, due to the fibers that were not previously rigid. Warmth and increased stress on the muscles shortly before death occurs accelerate the onset of rigor mortis. As a result of decomposition processes, the rigidity begins to dissolve again 24 to 48 hours post mortem at the latest, at the start of autolysis , and does not start again afterwards.
In order to be able to limit the time of death for the first time, rigor mortis is of great importance in forensic medicine . Among other things, the above-described facts are used, since it is only possible to determine the re-establishment of rigidity after the artificial breaking within a certain time frame post mortem.
Contrary to widespread rumors, “breaking” rigor mortis does not mean breaking bones, but rather the undertaker's joints are stretched and bent in order to be able to dress the deceased. In particular, the arm joints are made soft. The finger joints are easily clenched into a fist and straightened, usually then also folded and interlaced.
The general relaxation that often sets in after death has resulted in many cases in the jaw opening wide. In order to avoid this unwanted sight, doctors or nursing staff put a gauze bandage under the chin around the head as a preventive measure; after the onset of rigidity, this is then removed again.
- University of Regensburg: Adenosine triphosphate (ATP), building a muscle and rigor mortis ( Memento from September 30, 2007 in the Internet Archive ) (PDF; 296 kB)
- Rules for carrying out the medical examination guidelines of the German Society for Forensic Medicine, 10/2017
- Ingo Wirth, Hansjürg Strauch: Forensic medicine: Basic knowledge for investigative practice . CF Müller GmbH, 2006, ISBN 978-3-7832-0016-4 , p. 15.
- http://bestatterweblog.de/totenstarre-rigor-mortis/ from August 3, 2007.