True about Rigor mortis:
**Core Concept**
Rigor mortis is a temporary stiffness of the muscles that occurs after death, caused by a series of complex biochemical changes. This process involves the breakdown of ATP and the subsequent contraction of muscles due to the action of actin and myosin filaments.
**Why the Correct Answer is Right**
The correct answer is related to the biochemical changes that occur in the muscle cells during rigor mortis. After death, the muscle cells undergo a series of changes that lead to the depletion of ATP stores. As a result, the actin and myosin filaments in the muscle cells begin to interact and contract, leading to the characteristic stiffness of rigor mortis. This process is influenced by the enzyme **calpain**, which breaks down the muscle proteins and contributes to the development of rigor mortis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct biochemical mechanism underlying rigor mortis. While it is true that ATP depletion is involved, it does not provide a clear explanation of the process.
**Option B:** This option is incorrect because it implies that rigor mortis is a result of the action of a specific enzyme, which is not accurate. While enzymes such as calpain are involved in the process, they are not the primary cause of rigor mortis.
**Option C:** This option is incorrect because it does not provide a clear explanation of the biochemical changes that occur during rigor mortis. While it mentions the role of ATP, it does not provide a detailed explanation of the process.
**Clinical Pearl / High-Yield Fact**
Rigor mortis typically begins to set in about 2-4 hours after death and can last for several hours. It is an important forensic indicator that can be used to estimate the time of death.
**Correct Answer:** C.