Which system includes the brain and spinal cord?

The nervous system is the correct choice as it is the system that encompasses both the brain and spinal cord. The primary function of the nervous system is to receive, process, and transmit information throughout the body, allowing for coordination and response to various stimuli. The brain serves as the control center, integrating sensory information and managing higher cognitive functions, while the spinal cord acts as a major conduit for information traveling to and from the brain, connecting it with the peripheral nervous system.

This distinction is important, as the other systems listed serve entirely different functions: the digestive system is responsible for breaking down food and absorbing nutrients, the cardiovascular system manages blood circulation and transport of nutrients and oxygen, and the muscular system enables movement of the body. Understanding these systems and their specific roles is crucial in health assisting, as they each contribute to overall bodily function and health.