Patellar reflex - wikipedia Patellar reflex Schematic representation of patellar tendon reflex ( knee jerk ) pathway The patellar reflex or knee - jerk ( myotatic ) ( monosynaptic ) ( American spelling knee reflex ) is a stretch reflex which tests the L2, L3, and L4 segments of the spinal cord. Contents 1 Mechanism 2 Purpose of testing 3 History 4 In popular culture 5 See also 6 Notes 7 References Mechanism 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 ) 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 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. 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 ). 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. Purpose of testing 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. History 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. '' In popular culture 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. '' See also Look up knee - jerk in Wiktionary, the free dictionary. Tonic vibration reflex Motor control Jendrassik maneuver Notes Jump up ^ In American English, knee - reflex is the spelling of only the adjective, not the noun. ^ Jump up to : William J. Weiner ( 30 July 2010 ). Neurology for the Non-Neurologist. Lippincott Williams & Wilkins. pp. 499 --. ISBN 978 - 1 - 60547 - 239 - 3. Retrieved 4 July 2011. ^ Jump up to : Knee - jerk reaction References Gurfinkel ' VS, Lipshits MI, Popov KE ( 1974 ). `` Is the stretch reflex a basic mechanism in the system of regulation of human vertical posture ? ''. Biofizika ( in Russian ). 19 ( 4 ) : 744 -- 8. PMID 4425696. Pinnock CA, Lin ES, Smith T ( 2003 ). `` Fundamentals of Anaesthesia, 2nd Edition '' ( 2nd ed. ). Greenwich Medical Media Ltd. chapter = ignored ( help ) Nervous system physiology : neurophysiology - reflex Cranial nerve midbrain : Pupillary light reflex Accommodation reflex pons / medulla : Jaw jerk reflex Corneal reflex Caloric reflex test / Vestibulo - ocular reflex / Oculocephalic reflex Pharyngeal ( gag ) reflex Stretch reflexes upper limb : Biceps reflex C5 / C6 Brachioradialis reflex C6 Triceps reflex C7 / C8 lower limb : Patellar reflex L2 - L4 Ankle jerk reflex S1 / S2 Plantar reflex L5 - S2 Primitive reflexes Galant Gastrocolic Grasp Moro Rooting Stepping Sucking Tonic neck Parachute Superficial reflexes Abdominal reflex Cremasteric reflex Lists general alphabetical by organ Cardiovascular Bainbridge reflex Bezold - Jarisch reflex Coronary reflex Diving reflex Oculocardiac reflex Baroreflex Reflex bradycardia Reflex tachycardia Respiratory Churchill - Cope reflex Other Acoustic reflex H - reflex Golgi tendon reflex Optokinetic Startle reaction Withdrawal reflex ( Crossed extensor reflex ) Symmetrical tonic neck reflex Retrieved from `` https://en.wikipedia.org/w/index.php?title=Patellar_reflex&oldid=777638487 '' Categories : Examination of the knee Reflexes Hidden categories : Articles needing additional references from April 2016 All articles needing additional references CS1 Russian - language sources ( ru ) CS1 errors : chapter ignored Talk Contents About Wikipedia Deutsch Español Italiano Nederlands Polski Português Русский Svenska Українська 中文 Edit links This page was last edited on 28 April 2017, at 11 : 18. 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Question: the patellar knee jerk reflex is an example of
Answer: stretch reflex