Question

Which of the following causes rigor in skeletal muscle?

1) No action potentials in motoneurons
2) An increase in intracellular Ca₂⁺ level
3) A decrease in intracellular Ca₂⁺ level
4) An increase in adenosine triphosphate (ATP) level
5) A decrease in ATP level

Answer 1

Rigor in skeletal muscle is caused by a decrease in intracellular Ca²⁺ level and a decrease in ATP level. Additionally, a decrease in ATP level prevents the myosin heads from detaching from the actin-binding sites, further contributing to muscle rigidity.

Step-by-step explanation:

Rigor in skeletal muscle is caused by a decrease in intracellular Ca²⁺ level and a decrease in ATP level.

When the intracellular Ca²⁺ level decreases, the cross-bridges formed between myosin and actin cannot detach, resulting in muscle rigidity.

Additionally, a decrease in ATP level prevents the myosin heads from detaching from the actin-binding sites, further contributing to muscle rigidity.