WordNet

an automatic instinctive unlearned reaction to a stimulus (同)reflex response, reflex action, instinctive reflex, innate reflex, inborn reflex, unconditioned_reflex, physiological reaction
act of bending a joint; especially a joint between the bones of a limb so that the angle between them is decreased (同)flexure
(of leaves) bent downward and outward more than 90 degrees

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反射(刺激に対する無意識の反応) / 《複数形で》反射的な動き / (光などの)反射,反射光;映像 / 反射性の / (カメラが)レフ鋼の,反射型の

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/07/12 23:26:26」(JST)

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The withdrawal reflex (nociceptive or flexor withdrawal reflex) is a spinal reflex intended to protect the body from damaging stimuli.^[1] It is polysynaptic, causing stimulation of sensory, association, and motor neurons.^[1]

Example

When a person touches a hot object and withdraws their hand from it without thinking about it, the heat stimulates temperature and danger receptors in the skin, triggering a sensory impulse that travels to the central nervous system. The sensory neuron then synapses with interneurons that connect to motor neurons.^[2] Some of these send motor impulses to the flexors to allow withdrawal; some motor neurons send inhibitory impulses to the extensors so flexion is not inhibited - this is referred to as reciprocal innervation.^[3]

Crossed extension reflex following withdrawal reflex

Once a danger receptor (called 'nociceptor') has been stimulated, the signal travels via the sensory nerve to the posterior horn of the spinal cord. The nerve synapses with ipsilateral motor neurons that exit the anterior horn of the spinal cord and work to pull the injured body part away from danger within 0.5 seconds.^[1] At the same time the sensory neuron synapses with the ipsilateral motor neuron, it also synapses with the motor neuron in the contralateral anterior horn.^[3] This motor neuron stabilizes the uninjured side of the body (for instance, preparing the opposite leg to support the entire body weight when the other foot has stepped on a tack). At the same time as these two synapses, the sensory neuron also sends signals up the spinal cord to get motor neurons to contract muscles that shift the center of gravity of the body to maintain balance. This contralateral stimulation of motor neurons to stabilize the body is called the crossed extension reflex, and is a result of the withdrawal reflex (usually in the lower extremities). ^[4]

References

^ ^a ^b ^c Solomon; Schmidt; Adragna (1990). "13". In Carol, Field. Human Anatomy & physiology (2 ed.). Saunders College Publishing. p. 470. ISBN 0-03-011914-6.
^ Thibodeau, Gary; Patton, Kevin (2000). "7". In Schrefer, Sally. Structure & Function of the Body (11 ed.). Mosby, Inc. p. 170. ISBN 0-323-01082-2.
^ ^a ^b Seeley, Rod; Stephens, Trent; Philip Tate (1992). Allen, Deborah, ed. Anatomy and physiology (2 ed.). Mosby-Year Book, Inc.
^ Anatomy and Physiology, The Unity of Form and Function by Ken Saladin. Pg 505-506.

External links

Ole K. Andersen, SMI, Aalborg University - Physiological and Pharmacological modulation of the human nociceptive withdrawal reflex

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