jähmettyminen

Jähmettyminen is a Finnish term that translates roughly to stiffening or hardening, and it is used to describe several related phenomena in different disciplines. The word derives from the verb jähmettyä, meaning to become stiff or immovable. In practice, it can refer to a physiological state, a physical phase transition, or a behavioral response, depending on the context.

In medicine and forensic science, jähmettyminen commonly denotes rigor mortis, the postmortem stiffening of skeletal muscles. After death, ATP is no longer produced, causing cross-bridges between actin and myosin filaments to form and muscles to lose the ability to relax. The onset is typically a few hours after death, influenced by ambient temperature, body mass, and metabolic conditions; stiffness often becomes noticeable within 2–6 hours, peaks around 12 hours, and gradually subsides over the next one to several days as tissues decompose. Rigor mortis provides forensic investigators with useful information about the time of death and postmortem changes.

In living organisms, jähmettyminen can describe a freeze response or tonic immobility, a defensive state in which an individual becomes motionless in the face of threat. This behavior has been observed across species and is the subject of neurobiological study, with proposed involvement of brain regions such as the amygdala and periaqueductal gray, and functions related to predator avoidance.

In physics and materials science, the term refers to the solidification or freezing of a liquid into a solid, such as water turning to ice or metals cooling from a liquid to a crystalline state. This process involves a phase transition and the release of latent heat. The precise interpretation of jähmettyminen depends on the context in which it is used.