Root values for knee jerk reflex are:

Appeared in: AIIMS BHOPAL NO- 2018( Shift-2nd)

Explanation

The knee jerk reflex, also known as the patellar reflex, is a deep tendon reflex.
It is a monosynaptic reflex, meaning the sensory neuron synapses directly on the motor neuron.
The primary spinal nerve roots that mediate this reflex are L3 and L4.
The reflex involves the femoral nerve and results in the contraction of the quadriceps femoris muscle, causing knee extension.

Option A: The L1 and L2 nerve roots are primarily associated with the cremasteric reflex in males and hip flexion (iliopsoas muscle), not the knee jerk reflex.
Option B: The S1 and S2 nerve roots are responsible for the ankle jerk (Achilles) reflex and plantar flexion of the foot.
Option D: The S3 and S4 nerve roots, along with S2, are involved in the anocutaneous reflex (anal wink) and control of bladder and bowel sphincters. They do not contribute to the knee jerk reflex.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Spinal nerve root values for deep tendon reflexes as background academic context rather than a clinical decision trigger.
Nurses perform reflex testing as part of a standard neurological assessment to monitor for changes in a patient's condition.
An asymmetrical reflex (different on the left vs. right side) is often more clinically significant than symmetrically diminished or brisk reflexes and should be reported.
In patients with spinal cord injuries, the level of the injury can be estimated by determining the lowest level with an intact reflex.

How to Approach the Question

Identify the key term in the question: 'knee jerk reflex'.
Recall the major deep tendon reflexes and their associated spinal nerve roots from your study of neuroanatomy.
Specifically, remember that the knee jerk (patellar) reflex is linked to the lumbar plexus, specifically the lower lumbar segments.
Associate the patellar reflex with the quadriceps muscle and the femoral nerve, which originates from L2-L4.
Eliminate the other options: S1/S2 for the ankle, C5/C6 for biceps/brachioradialis, and C7 for triceps.
Select L3 and L4 as the primary roots for the knee jerk reflex.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 2 p. 1285-1287

E6 Medicine Macleod Clinical Examination 15e pp. 163-165, 161-163

Practise the full AIIMS BHOPAL NO- 2018( Shift-2nd)

Attempt every question from this paper in a timed mock, then review the full solution for each one.