In a reflex arc, which element detects the stimulus?

In a reflex arc, which element detects the stimulus?

• A. Integration center
• B. Receptor
• C. Motor neuron
• D. Effector

Answer: (B)

Detection of a stimulus happens at the receptor, a specialized sensory ending or cell that samples the external or internal environment. The receptor converts the energy of the stimulus into a receptor potential, which triggers an action potential in the adjacent sensory neuron. This signal then travels to the integration center (such as the spinal cord), where it’s processed and a command is sent through a motor neuron to the effector to produce a response. The integration center and motor pathways are involved in processing and output, but they do not detect the stimulus themselves—the receptor is the detection site.

Detection of a stimulus happens at the receptor, a specialized sensory ending or cell that samples the external or internal environment. The receptor converts the energy of the stimulus into a receptor potential, which triggers an action potential in the adjacent sensory neuron. This signal then travels to the integration center (such as the spinal cord), where it’s processed and a command is sent through a motor neuron to the effector to produce a response. The integration center and motor pathways are involved in processing and output, but they do not detect the stimulus themselves—the receptor is the detection site.