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The knee jerk is an example of the simplest type of reflex. When the knee is tapped, the nerve that receives this stimulus sends an impulse to the spinal cord, where it is relayed to a motor nerve. This causes the quadriceps muscle at the front of the thigh to contract and jerk the leg up. This reflex, or simple reflex arc, involves only two nerves and one synapse. The leg begins to jerk up while the brain is just becoming aware of the tap.
Other simple reflexes, the stretch reflexes, help the body maintain its balance. Every time a muscle is stretched, it reacts with a reflex impulse to contract. As a person reaches or leans, the skeletal muscles tense and tighten, tending to hold him and keep him from falling. Even in standing still, the stretch reflexes in the skeletal muscles make many tiny adjustments to keep the body erect.
The “hot stove” reflex is more complex, calling into play many different muscles. Before the hand is pulled away, an impulse must go from the sensory nerve endings in the skin to a center in the spinal cord, from there to a motor center, and then out along the motor nerves to shoulder, arm, and hand muscles. Trunk and leg muscles respond to support the body in its sudden change of position, and the head and eyes turn to look at the cause of the injury. All this happens while the person is becoming aware of the burning sensation. A reflex that protects the body from injury, as this one does, is called a nociceptive reflex. Sneezing, coughing, and gagging are similar reflexes in response to foreign bodies in the nose and throat, and the wink reflex helps protect the eyes from injury.
A conditioned reflex is one acquired as the result of experience. When an action is done repeatedly the nervous system becomes familiar with the situation and learns to react automatically, and a new reflex is built into the system. Walking, running, and typewriting are examples of activities that require large numbers of complex muscle coordinations that have become automatic.
re·flex(rē'fleks), Do not confuse this word with reflux.
See also: phenomenon.
reflex/re·flex/ (re´fleks) a reflected action or movement; the sum total of any particular automatic response mediated by the nervous system.
reflexNeurology A rapid involuntary response to a mechanical or chemical stimulus. See Ankle reflex, Axon reflex, Babinski's reflex, Baroreflex, Cat's eye reflex, Consensual light reflex, Corneal reflex, Deep tendon reflex, Diving reflex, Doll's eye reflex, Gag reflex, Galant reflex, Gastrocnemius reflex, H reflex, Hering-Breuer reflex, J reflex, Let-down reflex, Moro reflex, Patellar reflex, Peristaltic reflex, Pulmonary chemoreflex, Pupillary reflex, Rooting reflex, Triceps reflex, Vestibulo-ocular reflex, Westphal-Piltz reflex.
reflexrapid innate response by an effector (muscle or gland) to a stimulus detected by neural receptors and signalled by afferent nerves to neurons in the central nervous system whose efferent nerves activate the effector. reflex arc this neural pathway, including one or more synaptic connections. See also stretch reflex, tendon reflex (tendon jerk).
reflexinvoluntary and largely unconscious reaction in response to a peripheral stimulus; detected by an affector organ (e.g. tendon stretch receptors; heat-sensitive nerve endings within the skin), transmitted along afferent nerve fibres to central nervous system centres, and thence to an effector organ via efferent nerve fibres, e.g. skeletal muscle, causing distal limb movement, or sweat gland tissue, causing sweat flow and resultant cooling; see Table 1
Achilles reflex; ankle reflex deep tendon reflex triggered by percussion of Achilles tendon 5cm proximal to its insertion into posterior calcaneum; induces contraction of posterior muscle group (gastrocnemius and soleus) and brief plantarflexion of foot at ankle joint; demonstrates normal S1 function
deep tendon reflex; DTR involuntary contraction of skeletal muscle induced by sudden and brief lengthening or percussion of subserving tendon; magnitude increased in upper motor neurone lesions, and absent/greatly reduced in any type of lower motor neurone lesion, peripheral sensory neuropathy and the elderly; enhanced by isometric contraction (e.g. hand-clenching) at time of test
knee jerk reflex see reflex, patellar
motor reflex see reflex, deep tendon
muscle stretch reflex see reflex, deep tendon
patellar reflex; knee-jerk reflex; quadriceps reflex sudden contraction of anterior-thigh muscle group (quadriceps) and resultant lower-limb 'kick' action due to brief knee joint extension; induced by transitory lengthening/percussion of patellar tendon at midpoint, 2 cm inferior to inferior border of patella when leg is relaxed and hanging pendulously from 90° flexed knee; demonstrates normal L4 function
pilomotor reflex contraction of smooth muscle within skin; caused by cold-induced contraction of arrector piles muscles; induces appearance of 'gooseflesh'
plantar reflex plantar flexion of toes at metatarsophalangeal joints and foot withdrawal, away from stimulus; induced by a firmly moving stimulus across the plantar surface; normal response to plantar stimulation (contrast with response, extensor plantar)
postural reflex reflex contraction of trunk and other postural muscles; induced by excursion of the centre of gravity, to maintain upright stance (see reflex, spinal)
quadriceps reflex see reflex, patellar
spinal reflex response of longitudinal muscles surrounding the spine to sudden and imposed stretch; unexpected flexion (forward) or extension (backward) movements induce reflex contraction of the opposing spinal muscle group, maintaining the erect posture
tendon reflex see reflex, deep tendon
|Tendon stretch excited by percussion||Spinal nerve roots stimulated||Reflex response elicited|
|Biceps brachialis||C5-C6||Flexion of forearm at elbow|
|Triceps brachialis||C7-C8||Extension of forearm at elbow|
|Patellar||L3-L4||Knee joint extension|
|Achilles||S1-S2||Ankle joint plantarflexion|
accommodative reflex See reflex accommodation; near reflex.
reflex arc See pupil light reflex.
blinking reflex Blinking in response to various stimulations such as a light source or a mechanical threat. See retinotectal pathway.
cat's eye reflex A whitish, bright reflection observed in the normally black pupil in several conditions, such as leukocoria, retinoblastoma, Coats' disease or persistent hyperplastic primary vitreous. It resembles the reflection from the tapetum lucidum of a cat when a light is shined at night.
consensual light reflex See pupil light reflex.
corneal reflex 1. Blinking in response to a threat, or to tactile stimulation of the cornea, as for example when measuring objectively the corneal touch threshold. Associated responses include lacrimation and miosis. 2. Image formed by reflection of light from the cornea (Fig. R5). See aesthesiometer; Hirschberg's method; Krimsky's method; pupillometer; apparent strabismus.
direct light reflex See pupil light reflex.
eyeball compression reflex See oculocardiac reflex.
fixation reflex Psycho-optical reflex consisting of an involuntary movement of the eye (or eyes) aimed at placing on the foveola the retinal image of an object that was formed in the retinal periphery. See psycho-optical reflex; re-fixation reflex.
foveal reflex Tiny reflection from the concave surface of the foveal depression of the retina seen in ophthalmoscopy. It is not usually visible in old eyes.
fundus reflex Light reflected by the fundus of the eye, as seen in retinoscopy and ophthalmoscopy. It appears as a red glow in the plane of the pupil in retinoscopy. It is absent when the eye has a dense cataract. Syn. red reflex.
fusion reflex See motor fusion.
hemianopic pupillary reflex In hemianopia, a loss of pupillary constriction when light falls on the blind side of the retina while pupillary constriction is maintained when light stimulates the unaffected side of the retina. Syn. Wernicke's hemianopic pupil; Wernicke's pupillary reaction; Wernicke's pupillary reflex; Wernicke's sign.
indirect light reflex See pupil light reflex.
lacrimal reflex Secretion of tears in response to irritation of the cornea or conjunctiva as, for example, when first wearing contact lenses (hard in particular), but it may also be induced by eyestrain, glare, laughing, etc. Syn. lacrimation reflex; tearing reflex; weeping reflex. See lacrimal apparatus; tear secretion; Schirmer's test.
lacrimation reflex See lacrimal reflex.
light reflex 1. That light which appears in the pupil in retinoscopy. It is light reflected by the retina. Syn. retinoscopic light. 2. Any reflected light. See pupil light reflex.
near reflex Reflex evoked by a blurred retinal image, as when fixating from far to near. It consists of three responses: (1) increased convexity of the crystalline lens; (2) constriction of the pupils; and (3) convergence of the eyes. This reflex is not a pure reflex since each of the three components can act independently of the other two; convergence by means of prisms, accommodation by means of lenses and miosis by light stimulation. Syn. accommodative reflex; near-triad reflex; synkinetic near reflex. See mechanism of accommodation; reflex accommodation; accommodative response.
near-triad reflex See near reflex.
oculocardiac reflex A decrease in pulse rate following compression of the eyeball or traction on the extraocular muscles during ocular surgery. It may produce a systolic cardiac arrest. Syn. Ascher's phenomenon; Ascher's reflex; eyeball compression reflex.
optokinetic reflex See vestibulo-ocular reflex.
postural reflex A reflex which helps to maintain static or dynamic posture of the body, for example, the righting reflex, in which visual stimuli help to maintain a correct position of the head in space by activating the muscles of the neck and limbs. See static eye reflex.
psycho-optical reflex Reflexes involving the eye which are mediated by the occipital cortex such as the accommodative, fixation, fusion, version and vergence reflexes.
pupil reflex Any alteration of the pupil size in response to stimuli other than light (e.g. a sudden noise). See pupil light reflex.
pupil light reflex 1. Constriction of the pupil in response to light stimulation of the retina. The response of an eye to light stimulation can occur either with a light shining on it directly (the direct light reflex) or when the other eye is stimulated (the consensual or indirect light reflex). The reflex arc consists of four neurons beyond the ganglion cells. The first afferent neuron transmits nervous impulses from the retina to the two pretectal olivary nuclei, located on the lateral and anterior side of the super-ior colliculi, in response to light stimulation of the photoreceptors. The second neurons, called the internuncial neurons, connect each pretectal olivary nucleus to both Edinger-Westphal nuclei which form part of the oculomotor nuclei. The third efferent neurons connect the latter nuclei, via the third nerve (oculomotor nerve) to the ciliary ganglion where there is a synapse. The fourth efferent neurons connect the latter, via the short ciliary nerves, to the sphincter pupillae muscle of each iris and constrict the pupil. Light stimulation of the central region of the retina produces a greater pupillary response than peripheral stimulation. The efferent path for pupil constriction represents the parasympathetic innervation (Fig. R6). Note: recent research points to a different pathway for the second afferent neuron: almost all of the fibres from each pretectal olivary nucleus project to the contralateral Edinger-Westphal nucleus. 2. Dilatation of the pupil in response to a reduction of the light stimulation of the retina. It is effected by sympathetic innervation, which originates in the hypothalamus and descends down the brainstem to the ciliospinal centre (of Bulge), located between C8 and T2. From there fibres pass to the superior cervical ganglion in the neck, then efferent fibres ascend along the internal carotid artery until they join the ophthalmic division of the trigeminal nerve. The fibres reach the dilator pupillae muscle of the iris via the nasociliary and long ciliary nerves, which enter the eyeball behind the equator. Syn. light reflex. See pupillary fibres; retinotectal pathway; pretectum; efferent pupillary defect.
red reflex See fundus reflex.
re-fixation reflex This reflex occurs while fixating one object and another in the visual field attracts the attention. The eye then turns to fixate on the new object. This is a special case of the fixation reflex.
retinoscopic reflex See light reflex; retinoscope.
righting reflex See postural reflex.
static eye reflex A higher order postural reflex which helps to maintain the eye static with respect to the visual environment by action on the extraocular muscles (possibly via the utricular receptors of the vestibular system) during head or body movements. Syn. compensatory eye movements.
reflex tearing See lacrimal reflex.
tonic neck reflex Orientation of the head, eyes and body in response to proprioceptive information provided by the activity of the muscles of the neck. See proprioception.
vergence reflex A disjunctive fixation reflex in response to an object that moves closer or further than the original position of the fixation point. See disjunctive eye movements.
version reflex A conjugate fixation reflex in response to an object moving in the same frontal plane. See version.
vestibulo-ocular reflex A conjugate movement of the eyes in the direction opposite to a head movement. This reflex is triggered by stimulation of the semicircular canals. It is aimed at maintaining a stable image on the retina during head movement. This reflex responds best at high velocities and frequencies of the visual stimulus. At low velocities and frequencies the stabilization of the ret-inal image is attempted by the optokinetic reflex, which is triggered only by retinal stimulation: this latter reflex complements the vestibulo-ocular reflex. See nystagmus; optokinetic.
weeping reflex See lacrimal reflex.
Wernicke's pupillary reflex See hemianopic pupillary reflex.
white pupillary reflex See leukocoria.
Patient discussion about reflex
Q. Anyone have/hear of RSD (Reflex Sympathetic Dystrophy) CRPS etc ,I have Fibro too Reflex Synmpathetic Dystrophy or CRPS and I have Fibromyalgia any others with CNS problems