reflex
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reflex
[re´fleks]a reflected action or movement; the sum total of any particular automatic response mediated by the nervous system. A reflex is built into the nervous system and does not need the intervention of conscious thought to take effect.
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.
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.
Nerve pathway of a simple reflex. When the sensory nerve ending is stimulated, a nerve impulse travels along a sensory (afferent) neuron to the spinal cord. Here an association neuron transfers the impulse to a motor (efferent) neuron. The motor neuron carries the impulse to a muscle, which contracts and moves a body part.
abdominal r's contractions of the abdominal muscles about the navel on stimulating the abdominal skin. It indicates that the spinal cord from the eighth to the twelfth thoracic nerve is intact.
accelerator reflex an increase in heart rate in response to changes in intrathoracic pressure or respiratory rate; see also Bainbridge reflex and cardiac respiratory reflex.
accommodation reflex the coordinated changes that occur when the eye adapts itself for near vision; they are constriction of the pupil, convergence of the eyes, and increased convexity of the lens.
Achilles reflex ankle jerk.
acoustic reflex contraction of the stapedius muscle in response to intense sound.
anal reflex contraction of the anal sphincter on irritation of the anal skin.
ankle reflex Achilles reflex.
auditory reflex any reflex caused by stimulation of the vestibulocochlear nerve; especially momentary closure of both eyes produced by a sudden sound.
Babinski reflex see babinski reflex.
Babkin reflex see babkin reflex.
Bainbridge reflex a rise in pressure in, or increased distension of, the large somatic veins or the right atrium causes acceleration of the heart beat. Called also Bainbridge effect.
baroreceptor reflex the reflex responses to stimulation of baroreceptors of the carotid sinus and aortic arch, regulating blood pressure by controlling heart rate, strength of heart contractions, and diameter of blood vessels.
biceps reflex contraction of the biceps muscle when its tendon is tapped.
bite reflex strong closure of the jaws when the teeth or gums are stimulated.
Brain's reflex extension of a hemiplegic flexed upper limb when a person is in a quadrupedal posture; called also quadrupedal extensor reflex.
bulbocavernosus reflex (bulbospongiosus reflex) contraction of the bulbocavernous muscle in response to a tap on the dorsum of the penis; called also penile reflex.
cardiac respiratory reflex an increase in heart rate caused by an increase in respiratory rate that reduces venous return.
carotid sinus reflex slowing of the heartbeat when pressure is applied to the carotid artery at the level of the cricoid cartilage. See also carotid sinus syndrome.
Chaddock's reflex in lesions of the pyramidal tract, stimulation below the external malleolus causes extension of the great toe; called also Chaddock's sign.
chain reflex a series of reflexes, each serving as a stimulus to the next, making a complete activity.
ciliary reflex the movement of the pupil in accommodation.
ciliospinal reflex dilation of the ipsilateral pupil on painful stimulation of the skin at the side of the neck.
clasp-knife reflex clasp-knife rigidity.
conditioned reflex conditioned response.
conjunctival reflex closure of the eyelid when the conjunctiva is touched.
corneal reflex see corneal reflex.
cough reflex the sequence of events initiated by the sensitivity of the lining of the airways and mediated by the medulla as a consequence of impulses transmitted by the vagus nerve, resulting in coughing, i.e., the clearing of the passageways of foreign matter.
cremasteric reflex contraction of the ipsilateral cremaster muscle, drawing the testis upward, when the upper inner aspect of the thigh is stroked longitudinally.
deep reflex one elicited by a sharp tap on the appropriate tendon or muscle to induce brief stretch of the muscle.
digital reflex Hoffmann's sign (def. 2).
doll's eye reflex doll's eye phenomenon.
embrace reflex Moro reflex.
gag reflex elevation of the soft palate and retching which is elicited by touching the back of the tongue or the wall of the pharynx; called also pharyngeal reflex.
Areas that react in a gag reflex when touched.
gastrocolic reflex increase in intestinal peristalsis after food enters the empty stomach.
gastroileal reflex increase in ileal motility and opening of the ileocecal valve when food enters the empty stomach.
grasp reflex flexion or clenching of the fingers or toes on stimulation of the palm of the hand or sole of the foot.
Hering-Breuer r's see hering-breuer reflexes.
Hoffmann's reflex Hoffmann's sign (def. 2).
jaw reflex (jaw-jerk reflex) closure of the mouth caused by a downward blow on the passively hanging chin; rarely seen in health but very noticeable in corticospinal tract lesions.
knee reflex knee jerk.
light reflex
1. constriction of the pupil when a light is shone into the same (direct light reflex) or the opposite eye (indirect or consensual light reflex).
2. a luminous image reflected when light strikes the normal tympanic membrane.
lung r's Hering-Breuer reflexes.
Magnus and de Kleijn neck r's extension of both limbs on the same side, or one limb or part of a limb, with increase of tonus on the side to which the chin is turned when the head is rotated, and flexion with loss of tonus on the side to which the occiput points; it usually indicates decerebrate rigidity.
Mayer's reflex opposition and adduction of the thumb combined with flexion at the metacarpophalangeal joint and extension at the interphalangeal joint, on downward pressure of the index finger.
Mendel-Bekhterev reflex dorsal flexion of the second to fifth toes on percussion of the dorsum of the foot; in certain organic nervous disorders, plantar flexion occurs.
micturition reflex any of the reflexes necessary for effortless urination and subconscious maintenance of continence.
Moro reflex see moro reflex.
myotatic reflex stretch reflex.
neck righting reflex rotation of the trunk in the direction in which the head of the supine infant is turned; this reflex is absent or decreased in infants with spasticity.
nociceptive r's reflexes initiated by painful stimuli; see also nociceptor and pain.
oculocephalic reflex doll's eye phenomenon.
orbicularis pupillary reflex unilateral contraction of the pupil, followed by dilatation after closure or attempted closure of eyelids that are forcibly held apart.
palatal reflex (palatine reflex) stimulation of the palate causes swallowing. Called also swallowing reflex.
paradoxical pupillary reflex reversed pupillary reflex.
patellar reflex knee jerk.
penile reflex bulbocavernosus reflex.
pharyngeal reflex gag reflex.
pilomotor reflex the production of goose flesh on stroking of the skin.
placing reflex flexion followed by extension of the leg when the infant is held erect and the dorsum of the foot is drawn along the under edge of a table top; it is obtainable in the normal infant up to the age of six weeks.
plantar reflex plantar flexion of the foot when the ankle is grasped firmly and the lateral border of the sole is stroked or scratched from the heel toward the toes.
proprioceptive reflex a reflex that is initiated by stimuli arising from some function of the reflex mechanism itself.
psychogalvanic reflex decreased electrical resistance of the body due to emotional or mental agitation.
pupillary reflex
1. contraction of the pupil on exposure of the retina to light.
2. any reflex involving the iris, resulting in change in the size of the pupil, occurring in response to various stimuli, e.g., change in illumination or point of fixation, sudden loud noise, or emotional stimulation.
quadriceps reflex knee jerk.
quadrupedal extensor reflex Brain's reflex.
red reflex a luminous red appearance seen upon the retina in retinoscopy.
reversed pupillary reflex any abnormal pupillary reflex opposite of that which occurs normally; e.g., stimulation of the retina by light dilates the pupil. Called also paradoxical pupillary reflex.
righting reflex the ability to assume an optimal position when there has been a departure from it.
rooting reflex a reflex in the newborn in which stimulation of the side of the cheek or upper or lower lip causes the infant to turn the mouth and face to the stimulus.
Rossolimo's reflex in pyramidal tract lesions, plantar flexion of the toes on tapping their plantar surface.
spinal reflex any reflex action mediated through a center of the spinal cord.
startle reflex Moro reflex.
stepping reflex movements of progression elicited when the infant is held upright and inclined forward with the soles of the feet touching a flat surface; it is obtainable in the normal infant up to the age of six weeks.
stretch reflex reflex contraction of a muscle in response to passive longitudinal stretching.
sucking reflex sucking movements of the lips of an infant elicited by touching the lips or the skin near the mouth.
suck-swallow reflex rhythmical sucking and swallowing movements in an infant when a finger or nipple is placed in the mouth.
superficial reflex any withdrawal reflex elicited by noxious or tactile stimulation of the skin, cornea, or mucous membrane, including the corneal, pharyngeal, and cremasteric reflexes.
swallowing reflex palatal reflex.
tendon reflex contraction of a muscle caused by percussion of its tendon.
tonic neck reflex extension of the upper limb and sometimes the lower limb on the side to which the head is forcibly turned, with flexion of the contralateral limbs; seen normally in the newborn. If it persists into the second or third year of life, it indicates a neurologic disorder.
triceps reflex contraction of the belly of the triceps muscle and slight extension of the upper limb when the tendon of the muscle is tapped directly, with the limb flexed and fully supported and relaxed.
triceps surae reflex Achilles reflex.
vestibular r's the reflexes for maintaining the position of the eyes and body in relation to changes in orientation of the head.
vestibulo-ocular reflex nystagmus or deviation of the eyes in response to stimulation of the vestibular system by angular acceleration or deceleration or when the caloric test is performed.
vomiting reflex the reflex for vomiting, caused by reflexive stimulation of muscles of the gastrointestinal tract and throat; it is mediated by centers in the medulla oblongata and can be set in motion by a variety of stimuli. See also gag reflex.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
re·flex
(rē'fleks), Do not confuse this word with reflux.1. An involuntary reaction in response to a stimulus applied to the periphery, and transmitted to the nervous centers in the brain or spinal cord. Most deep reflexes are stretch or myotatic reflexes, elicited by striking a tendon or bone, causing stretching, even slight, of the muscle, which then contracts as a result of the stimulus applied to its proprioceptors.
See also: phenomenon.
See also: phenomenon.
2. A reflection.
[L. reflexus, pp. of reflecto, to bend back]
Farlex Partner Medical Dictionary © Farlex 2012
reflex
(rē′flĕks′)adj.
1. Physiology Being an involuntary action or response, such as a sneeze, blink, or hiccup.
2. Bent, turned, or thrown back; reflected.
3. Reflexed.
n.
1.
a. Physiology An involuntary response to a stimulus.
b. reflexes A person's ability to respond to new or changing stimuli: His quick reflexes make him a good taxi driver.
2. Psychology An unlearned or instinctive response to a stimulus.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.
reflex
Neurology 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.McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.
re·flex
(rē'fleks)An involuntary reaction in response to a stimulus applied to the periphery and transmitted to the nervous centers in the brain or spinal cord.
[L. reflexus, pp. of reflecto, to bend back]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
reflex
1. An automatic, involuntary and predictable response to a stimulus applied to the body or arising within it.
2. The point of light reflected from a curved smooth surface, such as the CORNEA.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
Reflex
A response, usually a movement, elicited by tapping on the nerve with a special hammer-like instrument.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
reflex
1. Involuntary response to a stimulus.
2. Reflection or an image formed by reflection (e.g. corneal reflex).
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.
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.
Fig. R5 Frontal view of the right eye
Fig. R6 A, pupils under low illumination
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
re·flex
(rē'fleks)Involuntary reaction to a stimulus applied to periphery and transmitted to nervous centers in brain or spinal cord.
[L. reflexus, pp. of reflecto, to bend back]
Medical Dictionary for the Dental Professions © Farlex 2012
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
A. Ok I would like to ask if any others with RSD would like to get to know each other it looks like they have groups ,no one without RSD can appreciate the pain and the way those who you love the most ,think you are a faker because some RSDers ,you can't see anything readily ,not being believed with Nerve pain thayt is worse than anything I have felt like being shot ,blown up ,Third Degree Burns well kinda like when the nerves stgart to grow back from Third degree burns but 24/7 and the same degree of p[ain since 1968 .IF RSD IS CAUGHT IN THE FIIRST YEAR IT CAN BE Reversed so yes I want knowledge (oops didnt mean caps(to yell)Thank You rsdno
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