<P> This test of a basic automatic reflex may be influenced by the patient consciously inhibiting or exaggerating the response; the doctor may use the Jendrassik maneuver as a distraction or diversion in order to ensure a more valid reflex test . </P> <P> After the tap of a hammer, the leg is normally extended once and comes to rest . The absence or decrease of this reflex is problematic, and known as Westphal's sign . This reflex may be diminished or absent in lower motor neuron lesions and during sleep . On the other hand, multiple oscillation of the leg (pendular reflex) following the tap may be a sign of cerebellar diseases . Exaggerated (brisk) deep tendon reflexes such as this can be found in upper motor neuron lesions, hyperthyroidism, anxiety or nervousness . The test itself assesses the nervous tissue between and including the L2 and L4 segments of the spinal cord . </P> <P> The term knee - jerk was recorded by Sir Michael Foster in his Textbook of physiology in 1877: "Striking the tendon below the patella gives rise to a sudden extension of the leg, known as the knee - jerk ." </P> <P> The term began to be used figuratively from the early 20th century onwards . O.O. McIntyre, in his New York Day - By - Day column in The Coshocton Tribune, October 1921, wrote: "Itinerant preacher stemming Broadway on a soap box . And gets only an occasional knee - jerk ." </P>

State the type of stimulus that would cause a knee jerk reflex to occur