Why does calcium ion concentration remain elevated during rigor mortis?

During rigor mortis, the concentration of calcium ions remains elevated primarily because the mitochondria cease producing ATP, which is crucial for the functioning of calcium pumps in muscle cells. Under normal conditions, the sarcoplasmic reticulum, a specialized organelle that stores calcium ions, actively pumps calcium back into its storage using ATP. This process keeps cytosolic calcium levels low during muscle relaxation.

However, after death, ATP production halts because the physiological processes that require energy cease. Without ATP, the calcium pumps cannot function properly. Consequently, calcium ions released into the cytoplasm from the sarcoplasmic reticulum cannot be reabsorbed. This inability to regulate calcium ion concentration leads to sustained muscle contraction, which is observed as rigor mortis.

The other options do not accurately represent the biochemical changes occurring during rigor mortis. For instance, while muscles do exhibit a state of contraction during rigor mortis, this is a result of elevated calcium levels rather than being the fundamental reason for the increased calcium concentration. Similarly, the sarcoplasmic reticulum does not continuously release calcium ions without the presence of ATP to manage and regulate its storage and release, and the notion that calcium ions are unnecessary for muscle tension is incorrect, as calcium is essential for