Which system runs through the spine?

• A. Respiratory system.
• B. Nervous system.
• C. Digestive system.
• D. Circulatory system.

Answer: (B)

The spine houses the spinal cord, which is the main conduit of the nervous system. The nervous system runs through and alongside the spine: signals travel from the brain down the spinal cord, and nerve roots exit at each level to reach muscles and sensory receptors. This arrangement enables movement, sensation, and reflexes. Other systems—respiratory, digestive, and circulatory—operate in distinct areas of the body and don’t form a single continuous pathway through the spine, so they aren’t the system that runs through the spine.