Which sequence correctly describes the parts of a reflex arc?

• A. Brain, spinal cord, motor neuron
• B. Axon hillock, dendrite, soma, axon
• C. Receptor → sensory neuron → integration → motor neuron → effector
• D. Neurotransmitter, receptor, neuron, muscle

Answer: (C)

A reflex arc is a simple neural circuit that starts with detection of a stimulus and ends with a response, going through a clear flow: receptor detects the stimulus, a sensory neuron carries that signal to an integration center (often in the spinal cord), a motor neuron sends the command to an effector like a muscle, and the effector carries out the response. This exact sequence—receptor → sensory neuron → integration → motor neuron → effector—captures how a reflex quickly translates a sensed event into a quick action, with the integration step typically happening in the spinal cord.

The other descriptions miss essential parts or arrange them incorrectly. One description focuses only on general brain and spinal cord components with a motor pathway, omitting the initial detection and the explicit processing center. Another describes parts of a neuron rather than the circuit flow of a reflex. The remaining option mentions neurotransmitter and receptor but skips the sequential neural path from sensing to processing to motor output, so it doesn’t describe the actual reflex arc sequence.