Which part of the nervous system controls voluntary activity?

The correct answer is the somatic nervous system, which is a crucial component of the peripheral nervous system. This system specifically is responsible for controlling voluntary movements of skeletal muscles. The somatic nervous system allows individuals to perform conscious activities, such as walking, writing, or any other deliberate physical action. It encompasses the motor neurons that facilitate these movements by sending signals from the central nervous system to the muscles.

The options that suggest the other systems focus on involuntary functions or do not directly relate to voluntary muscular control. For instance, the autonomic nervous system regulates involuntary functions such as heart rate, digestion, and breathing, which do not require conscious thought. The peripheral nervous system includes both voluntary (somatic) and involuntary (autonomic) activities, but it is the somatic branch that specifically pertains to voluntary control. The term "Cerebro spinal system" is less commonly used and does not refer to a recognized differentiation of control over voluntary versus involuntary actions in the way that the other systems do. Hence, focusing on the somatic nervous system correctly identifies the portion of the nervous system that governs voluntary activity.