Deep tendon reflexes that appear diminished become brisker when the patient forcefully clenches the teeth or interlocks the fingers and pulls. The Jendrassik maneuver augments the reflex mainly by:

• A Stretching the agonist muscle mechanically before tendon percussion
• B Directly increasing alpha motor neuron excitability within the anterior horn
• C Increasing gamma motor neuron drive and reducing tonic descending inhibition on the fusimotor system ✓
• D Suppressing Golgi tendon organ output from the tested limb

Explanation

Voluntary contraction of remote muscles increases supraspinal facilitation, raising gamma motor neuron activity and thereby sensitizing muscle spindles, so the same tendon tap evokes greater Ia afferent discharge and a larger reflex. The maneuver acts centrally, not by mechanical pre-stretch of the tested muscle, and it does not require direct alpha motor neuron activation or any change in Golgi tendon organ signaling.

Reference: Ganong's Review of Medical Physiology, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.