Question

Rigor mortis occurs because ________.

1) no ATP is available to release attached actin and myosin molecules
2) the cells are dead
3) sodium ions leak into the muscle causing continued contractions
4) proteins are beginning to break down, thus preventing a flow of calcium ions

Answer 1

Rigor mortis occurs when no ATP is available to detach myosin from actin, causing muscle stiffness postmortem. ATP is required for muscle relaxation following contractions, and its absence after death results in the fixed position of muscles in rigor mortis.

Step-by-step explanation:

Rigor mortis occurs because no ATP is available to release attached actin and myosin molecules. During life, muscle contractions are powered by ATP, which is crucial for both contraction and subsequent relaxation of muscles. ATP allows myosin heads to detach from actin-binding sites after a contraction has occurred. After death, ATP production ceases, and the amount of ATP diminishes, leading to a state in which the myosin heads remain bound to actin, resulting in the stiffening of muscles known as rigor mortis.

It's important to note that rigor mortis is a temporary condition. As the body continues to decompose postmortem, proteins begin to break down, including those in muscle fibers, which eventually leads to the relaxation of the muscles once more.

Answer 2

No ATP is available to release attached actin and myosin molecules.

Step-by-step explanation:

Two to six hours later after death, all skeletal muscles of the body become rigid and stiff. This situation is defined as Rigor mortis. It occurs from the lack of ATP along with the production of lactic acid. When breathing stopped permanently in the body, oxygen level also reduced; that’s why body muscles cannot go for any aerobic respiration to produce any ATP.

As we know already, during every muscle construction, ATP needs to break the cross-bridge between Myosin and Actin. So if there is no ATP produced in the body, separation of Myosin molecules from Actin molecules cannot happen anymore. This situation leads for rigor mortis.