What are the main components of a reflex arc?

What are the main components of a reflex arc?

• A. Receptor, sensory neuron, relay neuron in CNS, motor neuron
• B. Receptor, relay neuron in CNS, motor neuron, and effector
• C. Receptor, sensory neuron, motor neuron, and effector
• D. Receptor, sensory neuron, relay neuron in CNS, motor neuron, and effector

Answer: (D)

A reflex arc starts with something in the body acting as a receptor, which detects a stimulus. The message then travels via a sensory neuron toward the central nervous system. Inside the CNS, processing occurs through a relay neuron (an interneuron) that integrates the signal and sends a command via a motor neuron to an effector, such as a muscle or gland, producing a rapid response. Including all these parts—receptor, sensory neuron, relay neuron in the CNS, motor neuron, and effector—gives the complete reflex pathway. That’s why this option is the best choice. The other options miss one essential component: one excludes the effector, another lacks the sensory neuron, and the remaining one omits the relay neuron in the CNS.

A reflex arc starts with something in the body acting as a receptor, which detects a stimulus. The message then travels via a sensory neuron toward the central nervous system. Inside the CNS, processing occurs through a relay neuron (an interneuron) that integrates the signal and sends a command via a motor neuron to an effector, such as a muscle or gland, producing a rapid response. Including all these parts—receptor, sensory neuron, relay neuron in the CNS, motor neuron, and effector—gives the complete reflex pathway. That’s why this option is the best choice. The other options miss one essential component: one excludes the effector, another lacks the sensory neuron, and the remaining one omits the relay neuron in the CNS.