In a simple reflex arc, what is the sequence from sensory receptor to motor output, including spinal integration?

• A. Motor neuron activates the muscle after a receptor detects motor command.
• B. Sensory receptor detects stretch; afferent neuron enters the spinal cord via dorsal root; synapses directly with motor neuron in ventral horn (monosynaptic) or via interneuron (polysynaptic); motor neuron activates muscle.
• C. Interneurons send signals directly to the brain then to the muscle.
• D. Muscle contraction triggers sensory receptors in a loop.

Answer: (B)