Which sequence correctly outlines the pathway of a simple reflex arc from skin receptor to muscle?

Which sequence correctly outlines the pathway of a simple reflex arc from skin receptor to muscle?

• A. Receptor detects stimulus -> spinal cord -> brain -> muscle -> response
• B. Sensory neuron -> receptor -> reflex arc
• C. Receptor -> motor neuron -> effector -> response
• D. Receptor detects stimulus -> sensory neuron -> spinal cord (relay neuron) -> motor neuron -> effector (muscle) -> response

Answer: (D)