Patellar reflex
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The patellar reflex, also called the knee reflex or knee-jerk, is a stretch reflex which tests the L2, L3, and L4 segments of the spinal cord. Many animals, most significantly humans, have been seen to have the patellar reflex, including dogs, cats, horses, and other mammalian species. [1]
Mechanism
Striking of the
The patellar reflex is a clinical and classic example of the monosynaptic reflex arc.[3] There is no interneuron in the pathway leading to contraction of the quadriceps muscle. Instead, the sensory neuron synapses directly on a motor neuron in the spinal cord.[3] 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 in order to ensure a more valid reflex test.
Clinical significance
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
The patellar reflex is often tested in infants to test the nervous system.[7]
History
Wilhelm Heinrich Erb (1840–1921) and Carl Friedrich Westphal (1833–1890) simultaneously reported the patellar tendon or knee reflex in 1875.[8] 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."[9]
In popular culture
The term began to be used figuratively from the early 20th century onwards.
See also
- Tonic vibration reflex – Sustained contraction of vibrated muscle
- Motor control – Regulation of movement within organisms possessing a nervous system
- Jendrassik maneuver – Medical maneuver to test reflexes
References
- ^ ISBN 978-1-60547-239-3. Retrieved 4 July 2011.
- ISBN 978-0-12-370877-9, retrieved 2020-12-23
- ^ ISBN 978-0-12-385158-1, retrieved 2020-12-23
- ^ ISBN 978-0-443-10321-6, retrieved 2020-12-23
- ISBN 978-0-409-95042-7, retrieved 2020-12-23
- ^ "Endocrinology - Hyperthyroidism". Core Concepts of Pediatrics. Archived from the original on 22 June 2016.
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ignored (help) - ISBN 978-0-323-42876-7, retrieved 2020-12-23
- PMID 19892119.
- ^ a b Martin, Gary. "'Knee-jerk reaction' - the meaning and origin of this phrase". Phrasefinder.
Sources
- 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). "Physiology of the Nervous System". Fundamentals of Anaesthesia, 2nd Edition (2nd ed.). Greenwich Medical Media Ltd.