What is the first function of the nervous system?

• A. Protect the body from the external environment.
• B. Remove sensory input from the body.
• C. Respond appropriately to the sensory input.
• D. Collect sensory input from the body and external environment.

Answer: (D)

Collecting sensory input is how the nervous system begins. Receptors throughout the body and in the environment detect signals—like touch, temperature, pain, balance, and sights—and send that information to the brain and spinal cord. This data is the basis for all further processing and action. Without gathering input, there’s nothing to interpret or respond to, so collecting sensory information is the first and essential step.

The other ideas describe later parts of the process. Protecting the body is a protective outcome that results from processing information and triggering responses. Removing sensory input would leave the system without essential information. Responding to sensory input is what happens after the input has been collected and processed.