<Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (April 2016) (Learn how and when to remove this template message) </Td> </Tr> <P> Striking the patellar tendon with a reflex hammer just below the patella stretches the muscle spindle in the quadriceps muscle . This produces a signal which travels back to the spinal cord and synapses (without interneurons) at the level of L3 in the spinal cord, completely independent of higher centres . From there, an alpha motor neuron conducts an efferent impulse back to the quadriceps femoris muscle, triggering contraction . This contraction, coordinated with the relaxation of the antagonistic flexor hamstring muscle causes the leg to kick . This is a reflex of proprioception which helps maintain posture and balance, allowing to keep one's balance with little effort or conscious thought . </P> <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>

Parts of the reflex arc for the patellar reflex