Dr. Robinson tapped on a patient's knee with the little hammer, but failed to see the usual kick of the patellar reflex. Since this reflex only involves a few neurons, what part of the nervous system might the doctor most likely be concerned about?

Question

A.  parasympathetic nervous system
B.  central nervous system
C.  sympathetic nervous system
D.  peripheral nervous system

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content/Choose Answer
· What do you already know about components of the nervous system? What other information is related to the question?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

D.  peripheral nervous system

Clarify Question
· What is the key concept addressed by the question?
        o The question is asking you to think about the components of a knee-jerk reflex and understand which part of the nervous system is involved.
· What type of thinking is required?
        o This question is asking you to identify key components of a reflex arc and then evaluate which components belong to which part of the nervous system to predict which system the doctor would be concerned about potential damage to.

Gather Content/Choose Answer
· What do you already know about components of the nervous system? What other information is related to the question?
        o To solve this problem, you’ll need to apply your knowledge of the function and categorization of the nervous system and a reflex arc.The patellar hammer stretches the leg muscle and activates stretch receptors in the muscle which sends a neural signal through sensory neurons which travel to the dorsal root ganglion and into the spinal cord.  Within the spinal cord, the sensory neurons synapse directly to motor neurons which travel back down to the leg muscle and cause it to contract, raising the leg.  The sensory and motor neurons involved are part of the peripheral nervous system, although they synapse in the spinal cord, which is a part of the central nervous system.  If the patellar reflex is non-functional, then it is likely the result of damage to peripheral nerves (either sensory or motor).

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o If you figured out the correct answer, great!  If not, where in your thought process did things go wrong?   Did you remember that the sympathetic and parasympathetic systems are divisions of the autonomic nervous system which is controlled by the medulla oblongata in the brain (which is part of the central nervous system)? You may have thought that since the sensory and motor neurons synapse in the spinal cord, which is part of the central nervous system, that lack of a reflex response could be the result of damage to the spinal cord. This is a possibility, but if there was a serious spinal injury which may have paralyzed the patient’s legs, it is unlikely that the doctor would rely on a simple knee-jerk reflex to test the paralysis.  Thus, you can assume the doctor is concerned about the main components of the reflex arc, the sensory and motor neurons, which are part of the peripheral nervous system.