Question

Within several hours after death, human bodies enter a state called “rigor mortis,” where the muscles continue to contract and the tissues of the body “stiffen.” The muscles remain contracted for several days, persisting up until the point at which myofibrils in muscle cells begin to decompose. Given your knowledge of how muscles cells contract, provide a molecular explanation for this phenomenon of rigor mortis.

Answer 1

Muscle cell contraction mechanism:

Muscle cells are formed by two specific proteins called actin & myosin which together forms myofibrils. Each myofibrils are covered by sarcoplasmic reticulum which is a cytoplasmic layer of muscle fibre (myocyte) contains calcium storage sites.

When a nerve impulse reaches inside the muscle cells by the indentations of transverse tubules, the nerve impulse is carried to the sarcoplasmic reticulum which is assocated with transverse tuble. As a result calcium channels will open and calcium ions will move from sarcoplasmic reticulum and gets attached to troponin which are present on the surface of actin. This mechanism will results in opening of active sites actin. Now by consuming ATP myosine heads will change its angle and binds to active sites on actin. This mechanism will pull actin chain along with myosine fibres inside and causes muscle cells to contrct. To contract fully myosin heads will change its angle possition even more which pulls actin filaments inside resulting in more muscle contraction.

For complete relaxation, with the help of ATP calcium ions will move back to sarcoplasmic reticulum from trophonin which closes the active sites on surface of actin.

Rigot mortis is a condition of stiffening of body muscle after several hours if death.

When body stops breathing there will be a loss of oxygen supply to the body.

Even after death body can perform muscle contraction like normal mechanism.

When there is a lack of oxygen body cannot produce any more ATPs through aerobic respiration, so body will switch to anaerobic respiration. When there is a shortage of ATPs Myosin and actin filaments cannot come back to the relaxed state, so they remain contracted and calcium ions cannot be pumped back to the out of muscle cells.