Final answer:
The correct order for the leg extension reflex is Extensor Muscle, Sensory Afferent, Spinal Cord, Motor Efferent. This represents a somatic reflex arc sequence where the spinal cord processes the sensory input and directly initiates a motor response without brain involvement.
Step-by-step explanation:
When discussing the leg extension reflex and the proper order of afferent and efferent neuronal pathways to and from the spinal cord for the knee extensor, the correct sequence is C. Extensor Muscle, Sensory Afferent, Spinal Cord, Motor Efferent. This sequence reflects the typical reflex arc pathway where a stimulus, such as tapping on the tendon, activates sensory receptors - in this case, the muscle spindle within the extensor muscle. The generated impulse then travels along the sensory afferent neuron into the spinal cord, and without the need for processing by the brain, a response is elicited through the motor efferent neuron that causes the muscle to contract.
This reflex arc is an example of a somatic reflex, which differs from a visceral reflex in that the output is a lower motor neuron directly causing contraction of a skeletal muscle. The reflex acts as a quick, automatic response that maintains posture and balance, crucial for everyday movements and changes in muscle length. Reflex testing can indicate proper functioning of the lower motor neurons (LMNs) in the spinal cord and overall neural circuit health.