What is the correct order of the reflex arc?

Students must select 1 of the following:

a) Motor - Sensory - Relay b) Effector - Relay - Motor c) Sensory - Relay - Motor d) Relay - Motor - Sensory

The correct answer is C.

When a stimulus is detected by a sensory receptor (Sensory), this signal passes along the sensory neurons, to the spinal cord. Here, Relay neurons connect the sensory neurons to the motor neurons. The signal is passed along the Relay neurons. Connected to this are the Motor neurons, which carry the signal to the effectors. An example would be the knee reflex. A stimulus (tap) is detected by sensory neurons; passes through the relay neurons; and the motor neurons then pass the signal to the effector, which in this case, is the muscle to move the knee.