knee-jerk reflex

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Noun1.knee-jerk reflex - a reflex extension of the leg resulting from a sharp tap on the patellar tendon
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References in periodicals archive ?
Patellar reflex, also called knee-jerk reflex, is a sudden kicking movement of the lower leg in response to a sharp tap on the patellar tendon, which lies just below the kneecap.
By connecting the "branches" of their dendrites to the "root tips" of other neurons' axons, nerve cells form networks, which can be as simple as the few connections involved in the knee-jerk reflex or as complex as those in the human brain.
Pharyngitis is routinely mishandled, with treatment often given despite a negative rapid strep test, and intramuscular injections of ceftriaxone are often administered when a child's white blood cell count is greater than 15,000/[mm.sup.3] as a knee-jerk reflex despite the currently very low risk of occult bacteremia in low-risk children.