<P> The patellar reflex is a clinical and classic example of the monosynaptic reflex arc . There is no interneuron in the pathway leading to contraction of the quadriceps muscle . Instead, the bipolar sensory neuron synapses directly on a motor neuron in the spinal cord . However, there is an inhibitory interneuron used to relax the antagonistic hamstring muscle (Reciprocal innervation). </P> <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>

Is the patellar reflex an example of positive or negative feedback