[L. reflexus, bending back]
An involuntary response or action to a stimulus. Reflexes are specific and predictable and are usually purposeful and adaptive. They depend on an intact neural pathway between the stimulation point and a responding organ. This pathway is called the reflex arc. In a simple reflex this includes a sensory receptor, afferent or sensory neuron, reflex center in the brain or spinal cord, one or more efferent neurons, and an effector organ. Most reflexes, however, are more complicated and include internuncial or associative neurons intercalated between afferent and efferent neurons.
SEE: reflex arc for illus
Contraction of the muscles of the abdominal wall when the overlying skin is stimulated. Absence of this reflex indicates damage to the pyramidal tract.
A change in heart rate, usually a slowing, resulting from mechanical stimulation of abdominal viscera.
Any of the changes that take place as the eye adjusts to bring light rays into focus on the retina. It involves a change in the size of the pupil and the convexity of the lens, and either a convergence or divergence of the eyes.
SYN: near reflex
Achilles tendon reflex
acoustic blink reflex
Involuntary closure of the eyelids after exposure to a sharp, sudden noise. This is a normal startle response that may be exaggerated in patients with anxiety disorders or hyperacusis. It may be blunted in infants or adults with a hearing disorder or facial nerve paralysis.
SEE: Conditioned reflex.
Flexion of the forearm and internal rotation of the hand as a result of a quick blow to the acromion. It is elicited in hyperreflexic states.
Contraction of the adductor muscles of the thigh on applying pressure to or tapping the medial surface of the thigh or knee.
Any of the reflexes initiated by several stimuli originating in widely separated receptors whose impulses follow the final common path to the effector organ and reinforce one another.
Contraction of the anal sphincter following irritation or stimulation of the skin around the anus. This reflex is lost if the second to fourth sacral nerves are injured.
SYN: anal wink
ankle clonus reflex
A reflex elicited by quick, vigorous dorsiflexion of the foot while the knee is held in a flexed position, resulting in repeated clonic movement of the foot as long as it is maintained in dorsiflexion. In women with pregnancy-induced hypertension, this reflects hyperirritability of the central nervous system and increased risk for eclamptic convulsions.
Two or more reflexes initiated simultaneously in different receptors that involve the same motor center but produce opposite effects.
asymmetrical tonic neck reflex
In an infant, extension of one or both extremities on the side to which the head is forcibly turned. Flexion of the extremities occurs on the other side.
Change in the size of the pupil when attention is suddenly fixed.
The sudden turning of the head and eyes toward an alarming sound.
Any reflex produced by stimulation of the auditory nerve, esp. blinking of the eyes at the sudden unexpected production of a sound.
auriculocervical nerve reflex
SEE: Snellen reflex.
SEE: Kisch reflex.
Any reflex involving the response of a visceral effector (cardiac muscle, smooth muscle, or gland). Such reflexes always involve two efferent neurons (preganglionic and postganglionic).
A reflex that does not involve a complete reflex arc and hence is not a true reflex. Its afferent and efferent limbs are branches of a single nerve fiber, the axon (axon-like dendrite) of a sensory neuron. An example is vasodilation resulting from stimulation of the skin.
Flexion of the forearm on percussion of the tendon of the biceps brachii.
Sudden closing of the eyelids in response to turning of the head, loud noises, bright lights, or visual threats. Absence of this reflex occurs in blindness and in injuries to cranial nerves III, V, and VII.
SEE: Brain reflex
A reduced heart rate following pressure on the anterior fontanel.
SEE: Hering-Breur reflex.
SEE: Brissaud, Édouard
Contraction of bulbocavernosus muscle on percussing the dorsum of the penis.
SYN: virile reflex
SYN: Facial reflex
Contraction of bulbospongiosus muscle on percussing the dorsum of the penis.
An involuntary response consisting of a change in cardiac rate. Stimulation of sensory nerve endings in the wall of the carotid sinus by increased arterial blood pressure reflexively slows the heart (Marey law). Stimulation of vagus fibers in the right side of the heart by increased venous return reflexively increases the heart rate (Bainbridge reflex).
1. A sympathetic increase in heart rate when there is increased pressure in or distention of great veins.
2. Reflex vasoconstriction resulting from reduced venous pressure.
carotid sinus reflex
A slowing of the heart rate and a fall in blood pressure when the carotid sinus is massaged. Carotid sinus massage may be used therapeutically to treat paroxysmal supraventricular tachycardia.
cat's eye reflex
In children, an abnormal pupillary flash or reflection from the eye that may be momentary; may be white, yellow, or pink; and is best seen under diminished natural illumination. This reflex, which may be noticed first by a parent, may be caused by various conditions, the most important of which is retinoblastoma. It is also observed in tuberous sclerosis, inflammatory eye diseases, and some congenital malformations of the eye.
SEE: Chaddock reflex
A reflex initiated by several separate serial reflexes, each activated by the preceding one.
The normal contraction of the pupil in accommodation of vision from distant to near.
Dilation of the pupil after stimulation of the skin of the neck by pinching or scratching.
Quick inhibition of the stretch reflex when extensor muscles are forcibly stretched by flexing the limb.
Contraction of the orbicularis palpebrarum muscle resulting from a sudden noise produced near the ear.
SYN: cochleo-orbicular reflex
A reflex acquired as a result of training in which the cerebral cortex plays an essential part. Conditioned reflexes are learned, not inborn or inherited.
SYN: acquired reflex
Closure of eyelids when the conjunctiva is touched or threatened.
SEE: Crossed reflex.
consensual light reflex
The reaction of both pupils that occurs when one eye is exposed to a greater intensity of light than the other.
SEE: pupillary reflex
1. Passive flexion of one part following flexion of another.
2. Passive flexion of one leg, causing similar movement of the opposite leg.
A reflex induced by a weak stimulus and causing widespread uncoordinated and purposeless muscle contractions, seen in strychnine poisoning.
Closure of eyelids resulting from direct corneal irritation. This reflex is mediated by the fifth cranial nerve.
SYN: lid reflex
Deflexion of the mandible toward the opposite side when the cornea is irritated while the mouth is open and relaxed.
Any reflex whose origin is in the brain.
Retraction of the testis when the skin is stroked on the inner front side of the thigh.
crossed extension reflex
An extension of the lower extremity on the opposite side when a painful stimulus is applied to the skin.
1. The normal ability of an infant to cry. It is not usually present in premature infants.
2. The spontaneous crying by infants during sleep.
dartos muscle reflex
A wormlike contraction of the dartos muscle after a sudden application of cold to the perineum. When the dartos muscle fibers contract, the scrotal skin becomes wrinkled and is held close to the testes
SEE: Deep tendon reflex.
deep tendon reflex
ABBR: DTR An automatic motor response elicited by stimulating stretch receptors in subcutaneous tissues surrounding joints and tendons. The assessment of DTRs is typically made by striking a tendon (such as the Achilles or brachioradialis tendons) with a weighted hammer. Brisk or hyperactive responses are seen in conditions such as hyperthyroidism, stroke, preeclampsia, or spastic disorders. Diminished responses may be seen in patients with hypothyroidism, drug intoxication, and flaccid neuromuscular disorders.
SYN: deep reflex; muscle stretch reflex
SEE: clonus; knee-jerk reflex
Retraction or tension in response to an action or threatened action.
A reflex that does not occur until several seconds after the application of a stimulus.
A reflex that results in slowed muscle activity, as in the heart rate.
Sudden flexion of the terminal phalanx of a finger or thumb when the nail is suddenly tapped.
A reflex in which response occurs on the same side as the stimulus.
direct light reflex
Prompt contraction of the sphincter of the iris when light entering through the pupil strikes the retina.
Slowing of the heart rate when a person's head is immersed in water. This reflex helps to protect a person from drowning, esp. in cold water.
SEE: Lumbar reflex.
SEE: Triceps reflex.
A typical reflex common to all vertebrates that includes the postural, flexion, stretch, and extensor thrust reflexes.
SEE: Moro reflex.
Contraction of the upper portion of the rectus abdominis muscle when the skin of the epigastric region is scratched.
SEE: Erben reflex
erector spinae reflex
SEE: Lumbar reflex.
SEE: Escherich reflex
extensor plantar reflex
Extension of the great toe when the sole of the foot is stimulated.
SEE: Babinski, Joseph-François-Felix
extensor thrust reflex
A quick and brief extension of a limb when pressure is applied to its plantar surface.
An infantile reflex in which the tongue moves outward after it has been touched. It is present from birth to 4 months.
eyelid closure reflex
Muscular contraction resulting from percussing facial fascia.
Extension of the knee and flexion of the foot resulting from irritation of the skin over the upper anterior third of the thigh.
SEE: Tonic neck reflex.
flexor withdrawal reflex
Flexion of a body part in response to a painful stimulus.
SYN: withdrawal reflex
Contraction of the gastrocnemius muscle when stretched muscles of the extended leg are percussed.
Gagging and vomiting resulting from irritation of the throat or pharynx.
SEE: Galant reflex
A peristaltic wave in the colon induced by entrance of food into the stomach.
The physiological relaxation of the ileocecal valve resulting from food in the stomach.
SEE: Gault reflex
SEE: Geigel reflex
SEE: Gifford reflex
Blinking of the eyes when the forehead just above the bridge of the nose is tapped. In most people, blinking stops after a few taps on the forehead. If it does not, significant brain disease may be present, e.g., Parkinson disease or any disease that causes frontal lobe atrophy.
Contraction of the gluteal muscles from stimulation of the overlying skin.
SEE: Gordon reflex
The grasping reaction of the fingers and toes when they are stimulated. This reflex is normal in the newborn but disappears as the nervous system matures. It may reappear later in life if a person suffers an injury to the frontal lobes of the brain.
SEE: Grünfelder reflex
In electrodiagnostic studies of spinal reflexes, the time required for a stimulus applied to a sensory nerve to travel to the spinal cord and return down the motor nerve.
SEE: F response
SEE: Haab reflex
Any reflex, such as the Bainbridge reflex, in which the stimulation of a sensory nerve causes the heart rate to increase or decrease.
SEE: Hering-Breuer reflex
SEE: Hirschberg reflex.
SEE: Hoffmann, Johann
Slowness of the relaxation phase of deep tendon reflexes. It is present in hypothyroidism.
Sudden inspiration resulting from abrupt pressure below the costal border.
An unconditioned reflex; an innate or inherited reflex.
SEE: Crossed reflex.
Contractions of the musculature in the female groin when the upper thigh is scratched.
SEE: Geigel reflex
A scapular muscular contraction after percussion or stimulus between the scapulae.
A reflex involving several segments of the spinal cord.
SYN: long reflex
SEE: Myenteric reflex.
A reflex that involves only a single segment of the spinal cord.
SEE: Chin reflex.
SEE: Joffroy reflex
SEE: Juster reflex
SEE: Kisch reflex
SEE: Kocher reflex
labyrinthine righting reflex
A reflex, esp. a postural reflex, resulting from stimulation of receptors in the semicircular ducts, utricle, and saccule of the inner ear. This reflex helps orient the head in space and to the rest of the body.
SYN: kinetic reflex;optical righting reflex ;tonic labyrinthine reflex
Secretion of fluid after irritation of the corneal conjunctiva.
SEE: Landau reflex
Coughing from irritation of the larynx or fauces.
Uncontrollable laughter resulting from tickling or the fear of tickling.
The movement of breast milk from the alveoli into the lactiferous ducts in response to oxytocin-stimulated contractions. The reflex may be stimulated by suckling or by an infant's crying. Stimulation of the nipple increases the secretion of oxytocin. This technique may be used to stimulate contraction of the postpartum uterus.
SEE: Corneal reflex.
Constriction of the pupil when light is flashed into the eye.
The reflex movement of the lips when the angle of the mouth is suddenly and lightly tapped during sleep.
A reflex that does not involve the central nervous system, e.g., the myenteric reflex, which occurs even when extrinsic nerves to the intestine have been cut.
SEE: Lovén reflex
SEE: Lust reflex
Magnus-de Kleijn reflex
In decerebrate rigidity, extension of the limbs on the side to which the chin is turned by rotating the head. There is flexion of the limbs on the opposite side.
Clonic movement resulting from percussing or stroking the lower jaw.
Autonomic dysfunction that may occur as a late consequence of transection of the spinal cord. It is marked by episodes of sweating, bradycardia, hypotension, urinary incontinence, and muscular spasms of the legs.
SEE: Mayer reflex
SEE: Mendel, Kurt
SEE: McCormac reflex
A reflex involving only two neurons (afferent and efferent).
SEE: Moro reflex
muscle stretch reflex
SEE: Deep tendon reflex.
Reflex caused by distention of the intestine, resulting in contraction above the point of stimulation and relaxation below it.
SYN: intestinal reflex
SEE: Stretch reflex.
Sneezing resulting from irritation of nasal mucosa.
Contraction of the mentalis muscle with elevation of lower lip and wrinkling of skin of chin. The reflex is elicited by percussion of the side of the nose.
In a reclining infant, rotation of the trunk in the same direction in which the head is turned. This reflex appears at age 4 to 6 months and is no longer obtainable by age 2 years.
A reflex initiated by a painful stimulus.
Reduction of the opening of the naris on the affected side in lung disease in proportion to lessened alveolar air capacity on the affected side.
Contraction of the entire external obliquus muscle when the skin of the thigh below the inguinal ligament is simulated.
SEE: Aschner phenomenon
A form of blindism characterized by repetitive rubbing of the eyes with fingers or the hands.
The deviation of a person's eyes to the opposite side when the head is rapidly rotated. This is a normal finding in neonates. In adults it is indicative of coma.
SYN: doll's eye movement
SEE: Onanoff reflex
optical blink reflex
Involuntary closure of the eyelids after exposure to a bright light. Shining a bright light at an infant's eyes causes the eyes to blink and the head to flex backward. If this reflex is absent, further testing of cranial nerves II, III, IV, and VI is required.
optical righting reflex
Swallowing induced by stimulation of the soft palate.
palmar grasp reflex
A normal reflex in a the newborn in which the baby's fingers spontaneously curl around any object placed within them and do not spontaneously let go. This reflex usually diminishes by age 3 to 4 months and disappears before age 6 months. The reflex reappears later in life in diseases that affect the frontal lobes of the brain.
Swallowing induced by stimulation of the soft palate.
A contraction of the superficial muscles of the eye and chin produced on the same side as the palmar area that is stimulated by an examiner. This is an abnormal finding and indicates frontal disease.
Extension of an infant's arms, hands, and fingers when the infant is suspended in the prone position and dropped a short distance onto a soft surface. This reaction appears at age 9 months and persists. An asymmetrical response indicates a motor nerve abnormality.
SYN: parachute response
A response to a stimulus that is unexpected and may be the opposite of what is considered normal.
SEE: Knee-jerk reflex.
Any abnormal reflex due to disease.
1. Sudden downward movement of the penis when the prepuce or gland of a completely relaxed penis is pulled upward.
SYN: virile reflex
2. Contraction of the bulbocavernous muscle on percussing the dorsum of the penis.
SYN: virile reflex
3. Contraction of the bulbocavernous muscle resulting from compression of the glans penis.
SYN: virile reflex
An attempt to swallow when the pharynx is stimulated.
Piloerection when the skin is cooled or as a result of emotional reaction.
SEE: Piltz reflex
Flexion and then extension of an infant's leg that occurs when the infant is held erect and the dorsum of one foot is dragged along the underedge of a table top. This reflex lasts from birth until age 6 weeks.
SEE: plantar grasp
plantar grasp reflex
A grasp reflex resulting from gentle stimulation of the sole of the foot. This reflex lasts from birth until age 10 months.
SYN: sole reflex
Dilation of the pupil resulting from sharp pinching of the platysma myoides.
A change in the rate and rhythm of the heart and blood pressure when an irritant vapor is inhaled.
A change in respiratory depth and rate, coughing, suffocation, and pulmonary edema when an irritant vapor is inhaled.
Any reflex concerned with maintaining posture.
A reflex in which the response to stimulation is an increase in blood pressure caused by constriction of arterioles.
A reflex initiated by body movement to maintain the position of the moved part; any reflex initiated by stimulation of a proprioceptor.
Decreased electric resistance of the skin in response to emotional stress or stimuli.
1. Constriction of the pupil upon stimulation of the retina by light. This reflex is mediated by the third cranial nerve.
2. Constriction of the pupil upon accommodation for near vision, and dilatation upon accommodation for far vision.
3. Constriction of the pupil of one eye in response to stimulation of the other by light.
4. Constriction of the pupil upon attempted closure of eyelids that are held apart.
SEE: Purkinje phenomenon.
SEE: Knee-jerk reflex.
Extension of the flexed arm on assuming a quadrupedal posture.
quadrupedal extensor reflex
SEE: Brain reflex.
Flexion of forearm resulting when the lower end of the radius is percussed.
The normal desire to evacuate feces present in the rectum.
red eye reflex
SEE: Red reflex
The red light reflection seen in ophthalmoscopic examination of the eye.
SYN: red eye reflex
Any of the reflexes that enable an animal to maintain its body in a definite relationship to its head and thus maintain its body right side up.
The turning of an infant's mouth toward the stimulus when the infant's cheek is stroked. This reflex is present at birth; by age 4 months it is gone when the infant is awake; by age 7 months it is gone when the infant is asleep.
SEE: Rossolimo reflex
SEE: Ruggeri reflex
Muscular contraction following percussion or stimulus between the scapulae.
A reflex in which the upper arm is adducted and rotated outward when the vertebral border of the scapula is percussed.
SEE: Schäffer reflex
Slow vermicular contraction of the scrotal muscle when the perineum is stroked or cold is applied.
A reflex in which afferent impulses enter the cord in the same segment or segments from which the efferent impulses emerge.
A reflex concerned with sexual activities, esp. erection and ejaculation, which results from direct genital stimulation or indirectly from emotion, whether the individual is asleep or awake.
A reflex involving one or a few segments of the spinal cord.
A reflex in which only two or possibly three neurons are interposed between receptor and effector organs.
SEE: Snellen, Herman
solar sneeze reflex
A sneeze following exposure to bright sunlight. This reflex is and affects a great number of normal people; it may also be associated with rhinitis. The mechanism of the cause of this type of sneeze reflex is unknown.
A reflex induced by stimulation of somatic sensory nerve endings.
A reflex whose center is in the spinal cord.
SEE: Moro reflex.
A reflex concerned with establishing and maintaining posture when the body is at rest.
A reflex that occurs when the body is moving.
Movements of progression elicited by holding an infant upright, inclined forward, and touching the soles of the feet to a flat surface. This reflex lasts from birth to age 6 weeks.
The contraction of a muscle caused by quick stretching of that muscle. Stretch reflexes are of primary importance in the maintenance of posture.
SYN: myotatic reflex
A sucking movement of an infant's mouth produced by stroking the lips. A primitive form of this reflex is present in the fetus by the 16th week of gestation; it is fully developed by the time of birth. In adults, the presence of a sucking reflex is an indicator of severe dementia, frontal lobe disease, or extrapyramidal diseases.
A cutaneous reflex caused by irritation of the skin or of areas that depend on the spinal cord as a motor center (such as the scapular, epigastric, and plantar reflexes) or on centers in the medulla (such as the conjunctival, pupillary, and palatal reflexes). This reflex is induced by a very light stimulus, e.g., stroking the skin lightly with a soft cotton swab.
Deflection of the linea alba toward the stroked side when the abdomen is stroked above the inguinal ligament.
Involuntary muscular activity in the oropharynx and nasopharynx when foods, tongue depressors, or other objects stimulate the back of the throat. This reflex is mediated by the deglutition center of the medulla oblongata, i.e., by cranial nerves VII, IX, X, and XI.
symmetrical tonic neck reflex
In an infant, flexion or extension of the arms in response to flexion and extension, respectively, of the neck.
A deep reflex obtained by sharply tapping the skin over the tendon of a muscle. It is exaggerated in upper neuron disease and diminished or lost in lower neuron disease.
testis compression reflex
Contraction of abdominal muscles following moderate compression of a testis.
SEE: Throckmorton reflex
A reflex in which strong flexion of the great toe flexes all the muscles below the knee.
Adduction of either the stimulated leg or the opposite one when the tibia is percussed on the inner side.
tonic labyrinthine reflex
tonic neck reflex
The ipsilateral extension and contralateral flexion of the supine infant's extremities when the head is turned to one side. This normal newborn reflex may not be evident immediately after birth; however, once it appears, it persists until about the third postnatal month.
SYN: fencing reflex
tonic vibration reflex
ABBR: TVR A polysynaptic reflex believed to depend on spinal and supraspinal pathways.
triceps surae reflex
true autonomic reflex
A visceral response in which afferent impulses do not pass through the central nervous system but enter prevertebral ganglia where connections are made with efferent neurons.
A reflex that is not acquired but is natural or inherited.
A spinal cord reflex, initiated by accumulated urine stretching the bladder and the resulting contraction of the bladder to expel urine.
SEE: Vasomotor reflex.
The constriction or dilatation of a blood vessel in response to a stimulus, as in becoming pale from fright.
SYN: vascular reflex
An inclination to urinate caused by moderate bladder distention.
A reaction that stabilizes the position of the head according to sensory information from the labyrinth of the ear and the nerves in the neck.
Any reflex induced by stimulation of the visceral nerves.
Contraction or tenseness of the skeletal muscles resulting from painful stimuli originating in visceral organs.
Pain or tenderness elicited in somatic structures (skin and muscle) caused by visceral disorder.
SEE: referred pain
The movement of the lower jaw toward the percussed side when the zygomatic bone is percussed.