- Patellar reflex
The patellar reflex or knee-jerk is a
stretch reflex and is amyotatic reflex .Mechanism
Striking the
patella rtendon with atendon hammer just below the patella stretches thequadriceps tendon . This stimulates stretchsensory receptors (most importantly,muscle spindle s) that triggers an afferent impulse in a sensory nerve fiber of thefemoral nerve leading to the lumbar region of the spinal cord. There, the sensory neuron synapses directly with amotor neuron that conducts an efferent impulse to thequadriceps femoris muscle , triggering contraction. This contraction, coordinated with the relaxation of the antagonistic flexor hamstring muscle causes the leg to kick. This reflex helps maintainposture and [http://ofinterest.net/patellar/ balance] , allowing one to walk without consciously thinking about each step.The patellar reflex is a clinical and classic example of the monosynaptic reflex arc. There is no
interneuron in the pathway leading to flexion of the quadriceps muscle. Instead the bipolar sensory neuron synapses directly on a motor neuron in the spinal cord. [William F. Ganong, MD, Review of Medical Physiology, McGraw Hill, 2005, ISBN 0-8385-8282-6] However, there "is" an inhibitory interneuron used to relax the antagonistic hamstring muscle.Purpose of Testing
Testing the
patellar tendon reflex tests the function of thefemoral nerve andspinal cord segments L2-L4.The absence or decrease of this reflex is known as
Westphal's sign .History
The term "knee-jerk" was coined 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." [http://www.phrases.org.uk/meanings/220600.html Knee-jerk reaction ] ]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 inThe Coshocton Tribune , October 1921, wrote: "Itinerant preacher stemming Broadway on a soap box. And gets only an occasional knee-jerk."Notes
References
*cite journal |author=Gurfinkel' VS, Lipshits MI, Popov KE |title=Is the stretch reflex a basic mechanism in the system of regulation of human vertical posture? |language=Russian |journal=Biofizika |volume=19 |issue=4 |pages=744–8 |year=1974 |pmid=4425696
See also
*
Tonic vibration reflex
*Motor control
*Jendrassik maneuver
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См. также в других словарях:
patellar reflex — n KNEE JERK * * * the knee jerk, in which stretching the muscle at the front of the thigh by tapping its tendon below the knee cap causes a reflex contraction of the muscle, so that the leg kicks. This is a test of the connection between the… … Medical dictionary
Patellar reflex — Reflex Re flex (r? fl?ks; formerly r?*fl?ks ), n. [L. reflexus a bending back. See {Reflect}.] 1. Reflection; the light reflected from an illuminated surface to one in shade. [1913 Webster] Yon gray is not the morning s eye, Tis but the pale… … The Collaborative International Dictionary of English
patellar reflex — n. Med. a normal reflex kick with extension of the leg at the knee, produced by sharply tapping the tendon below the patella * * * … Universalium
patellar reflex — n. Med. a normal reflex kick with extension of the leg at the knee, produced by sharply tapping the tendon below the patella … English World dictionary
patellar reflex — noun a reflex extension of the leg resulting from a sharp tap on the patellar tendon • Syn: ↑knee jerk, ↑knee jerk reflex • Hypernyms: ↑reflex, ↑reflex response, ↑reflex action, ↑instinctive reflex, ↑ … Useful english dictionary
patellar reflex — knee jerk reflex contraction of the quadriceps (thigh) muscle so that the leg kicks, elicited in a patient sitting with one knee crossed over the other by sharply tapping the tendon of the muscle below the kneecap. The reflex is mediated through… … The new mediacal dictionary
patellar reflex — noun The reflex which causes a bent knee to kick when the tendon below the patella (kneecap) is tapped. Syn: kneejerk reflex … Wiktionary
patellar reflex. — See knee jerk. [1890 95] * * * … Universalium
patellar reflex. — See knee jerk. [1890 95] … Useful english dictionary
Рефлекс Коленный (Patellar Reflex) — рефлекс, возникающий в ответ на кратковременное растяжение четырехглавой мышцы бедра легким ударом по ее сухожилию ниже надколенника, при котором наблюдается внезапное сокращение четырехглавой мышцы бедра; в результате голень разгибается (рефлекс … Медицинские термины
