This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Physiology
Lowest level of Integration of Stretch reflex is at? 
Select and explain. 
A. Cerebral cortex, B. Medulla, C. Lower medulla, D. Spinal Cord
D: Spinal Cord
Answer: D: Spinal Cord 
Explanation: Ans. D Spinal CordRef: Ganong's Physiology, 23rd ed. chapter 9* When a skeletal muscle with an intact nerve supply is stretched, it contracts. This response is called the stretch reflex.* The stimulus that initiates the reflex is stretch of the muscle, and the response is contraction of the muscle being stretched.* The sense organ is a small encapsulated spindle like or fusiform shaped structure called the muscle spindle, located within the fleshy part of the muscle.* The impulses originating from the spindle are transmitted to the CNS by fast sensory fibers that pass directly to the motor neurons which supply the same muscle.* The neurotransmitter at the central synapse is glutamate. The stretch reflex is the best known and studied monosynaptic reflex and is typified by the knee jerk reflex.