Final answer:
The somatic nervous system is responsible for sending signals to Ark's leg muscles to contract and enable him to run during the marathon. It is a part of the motor division of the peripheral nervous system that controls voluntary movements.
Step-by-step explanation:
The division of the nervous system responsible for sending signals to Ark's leg muscles during the marathon is the somatic nervous system. This system controls voluntary movements, like running. The somatic nervous system sends signals from the brain through motor neurons to the specific muscles that need to contract, initiating movement. As Ark runs, his nervous system continuously works to gauge muscle tension and body position to maintain balance and speed.
These signals are part of the motor division of the peripheral nervous system, which includes both the somatic nervous system and the autonomic nervous system. The somatic nervous system is specifically in charge of actions that are under conscious control, which in Ark's case, involve running in the marathon.
The sliding filament theory of muscle contraction is a physiological mechanism that describes how these muscle contractions occur at the molecular level after they receive signals from the somatic nervous system.