Which cell type acts as an intermediary within reflex pathways to connect sensory input to motor output?

• A. Interneurons
• B. Motor neurons
• C. Sensory neurons
• D. Purkinje cells

Answer: (A)

Interneurons act as the relay stations inside the central nervous system that connect sensory input to motor output. In a reflex, a detected stimulus sends a signal along a sensory neuron into the spinal cord. Instead of going directly to a motor neuron, that signal often is transferred to an interneuron, which processes the information and then activates a motor neuron to elicit a quick muscle response. This setup lets the body rapidly respond and can include modulation of the response through inhibition or excitation as needed. Purkinje cells are cerebellar neurons involved in coordinating movement, not the direct relay in a basic reflex arc. Motor neurons carry the command from the CNS to the muscle, and sensory neurons bring the message into the CNS, but the intermediary role between input and output in many reflex pathways is fulfilled by interneurons.