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The patellar reflex or knee-jerk is a deep tendon reflex and is a myotatic reflex. ==Mechanism== Striking the patellar ligament 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 L4 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 reflex is a reflex of proprioception which helps maintain posture and balance, allowing to keep one's balance with little effort or conscious thought. 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). It tests L2, L3, and L4. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「patellar reflex」の詳細全文を読む スポンサード リンク
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