The nervous system includes which structures?

• A. The circulatory system
• B. The nervous system
• C. The digestive system
• D. The respiratory system

Answer: (B)

The nervous system is defined by its components and function as the body's control network. It includes the brain, spinal cord, and a vast network of nerves that transmit signals, along with sense organs that detect stimuli and relay information to the nervous system. This system coordinates sensation, movement, and homeostasis by processing information and sending instructions to muscles and glands.

The other options are part of different body systems: the circulatory system involves the heart and blood vessels, the digestive system includes the stomach and intestines, and the respiratory system involves the lungs and airways. Therefore, the structures that make up the nervous system are the neural elements and associated sensory structures, not the components of those other systems.