Startle reflex Health Dictionary

A form of complementary medicine in which the practitioner massages parts of the patient’s feet in an attempt to treat disorders affecting other areas of the body.... reflexology

An action that occurs automatically and predictably in response to a particular stimulus, independent of the will of the individual.

In the simplest reflex, a sensory nerve cell reacts to a stimulus, such as heat or pressure, and sends a signal along its nerve fibre to the central nervous system. There, another nerve cell becomes stimulated and causes a muscle to contract or a gland to increase its secretory activity. The passage of the nerve signal.

from original sensation to final action is called a reflex arc.

Reflexes may be inborn or conditioned. Some inborn reflexes occur only in babies (see reflex, primitive). Inborn reflexes include those that control basic body functions, such as contraction of the bladder after it has filled beyond a certain point, and are managed by the autonomic nervous system. Conditioned reflexes are acquired through experience in a process called conditioning.

Several simple reflexes, such as the knee-jerk, are tested in a physical examination. Changes in the reflexes may indicate damage to the nervous system. The examination of vital reflexes controlled by the brainstem is the basis for diagnosing brain death.... reflex

When a sharp body is drawn along the sole of the foot, instead of the toes bending down towards the sole as usual, the great toe is turned upwards and the other toes tend to spread apart. After the age of about two years, the presence of this re?ex indicates some severe disturbance in the upper part of the central nervous system. The Babinski re?ex may occur transiently during COMA or after an epileptic ?t and need not indicate permanent damage.... babinski reflex

The development of a speci?c response by an individual to a speci?c stimulus. The best-known conditioned re?ex is the one described by Ivan Pavlov, in which dogs that became accustomed to being fed when a bell was sounded salivated on hearing the bell, even if no food was given. The conditioned re?ex is an important part of behavioural theory.... conditioned reflex

Instinctive closing of the eyelids when the surface of the cornea (see EYE) is lightly touched with a ?ne hair.... corneal reflex

A cough induced by intestinal, gastric or uterine irritation, and not from respiratory causes.... cough, reflex

Roxb.

Family: Convolvulaceae.

Habitat: A parasitic climber common throughout India up to 3,000 m.

English: Doddar.

Ayurvedic: Amarvalli.

Unani: Kasoos.

Action: See C. epithymum.

The seeds contain amarbelin and kaempferol; stem gave cuscutin, cuscu- tatin, beta-sitosterol, luteolin, bergenin and kaempferol. The parasitic plant accumulates alkaloids from the host plant. The climber growing on Mangi- era indica has been found to contain mangiferin.... cuscuta reflexa

Assessment of victims of major trauma must include maintenance of their airways and breathing. Any false teeth, vomitus and foreign bodies should be removed, and the response to digital stimulation of the posterior pharyngeal wall – the ‘gag re?ex’ – assessed. Even with a normal gag re?ex, the airway may be seriously threatened if vomiting occurs. During the initial stages of resuscitation, careful and constant supervision of the airway is essential, with a high-volume sucker immediately available. If the gag re?ex is absent or impaired, an endotracheal tube should be inserted (see ENDOTRACHEAL INTUBATION).... gag reflex

A ‘protective’ cough occurring as a result of irritation of the LARYNX – for example, a small particle of food may be accidentally ‘inhaled’ into the larynx, which reacts with an expulsive cough to prevent the food from entering the lungs.... laryngeal reflex

Pupillary constriction in the EYE in response to light. The direct light re?ex involves pupillary constriction in the eye into which a light is shone; the consensual light re?ex is the pupillary constriction that occurs in the other eye. The a?erent or inward pathway of the re?ex is via the optic nerve, and the e?erent or outward pathway is via the occulomotor nerve.... light reflex

A primitive REFLEX ACTION occurring in newly born infants in response to a sudden movement or noise. Also known as the startle re?ex, the baby will throw its arms and legs wide and sti?en its body. This is followed by ?exion of the arms and legs. The re?ex disappears by four months; its persistence suggests a possible neurological condition such as CEREBRAL PALSY.... moro reflex

See REFLEX ACTION.... patellar reflex

One of the simplest forms of activity of the nervous system. (For the mechanism upon which it depends, see NERVOUS SYSTEM; NEURON(E).) Re?ex acts are divided usually into three classes.

Super?cial re?exes comprise the sudden movements which result when the skin is brushed or pricked, such as the movement of the toes that results from stroking the sole of the foot.

Deep re?exes depend upon the state of mild contraction in which muscles are constantly maintained when at rest, and are obtained, as in the case of the knee-jerk (see below), by sharply tapping the tendon of the muscle in question.

Visceral re?exes are those connected with various organs, such as the narrowing of the pupil when a bright light is directed upon the EYE, and the contraction of the URINARY BLADDER when distended by urine.

Faults in these re?exes give valuable evidence as to the presence and site of neurological disorders. Thus, absence of the knee-jerk, when the patellar tendon is tapped, means some interference with the sensory nerve, nerve-cells, or motor nerve upon which the act depends – as, for example, in POLIOMYELITIS, or peripheral NEURITIS; whilst an exaggerated jerk implies that the controlling in?uence exerted by the BRAIN upon this re?ex mechanism has been cut o? – as, for example, by a tumour high up in the SPINAL CORD, or in the disease known as MULTIPLE SCLEROSIS (MS).... reflex action

Eye movement that occurs after or during the slow injection of 20 ml of ice-cold water into each external auditory meatus (see EAR) in turn.... vestibulo-ocular reflex

An automatic movement in response to a stimulus that is present in newborn infants but disappears during the first few months after birth. Primitive reflexes are believed to represent actions that were important in earlier stages of human evolution. They include the grasp reflex when something is placed in the hand and the rooting reflex, which enables a baby to find the nipple. The rooting reflex can be evoked by touching the baby’s cheek with the fingertip. These reflexes are tested after birth to give an indication of the condition of the nervous system.... reflex, primitive

(convergence reflex) a reflex that occurs when an individual focuses on a near object, in which the crystalline lens becomes more convex, the pupils constrict, and the eyes turn inwards.... accommodation reflex

a primitive reflex that is present from birth but should disappear by six months of age. If the infant is lying on its back and the head is turned to one side, the arm and leg on the side to which the head is turned should straighten, and the arm and leg on the opposite side should bend (the ‘fencer’ position). Persistence of the reflex beyond six months is suggestive of *cerebral palsy.... asymmetric tonic neck reflex

see plantar reflex. [J. F. F. Babinski (1857–1932), French neurologist]... babinski reflex

reflex control of the heart rate. Sensory fibres in the walls of the heart are stimulated when the heart rate increases above normal. Impulses are sent to the cardiac centre in the brain, stimulating the vagus nerve and leading to slowing of the heart rate.... cardiac reflex

a reflex in which the response occurs not to the sensory stimulus that normally causes it but to a separate stimulus, which has been learnt to be associated with it. In Pavlov’s classic experiments, dogs learned to associate the sound of a bell with feeding time and would salivate at the bell’s sound whether food was then presented to them or not.... conditioned reflex

reflex blinking of both eyes normally elicited by lightly touching the cornea of one eye. This reflex is lost in deep coma, during general anaesthesia, and in death; it is therefore one of the tests used to confirm brainstem death.... corneal reflex

a superficial reflex in males elicited by stroking the inner side of the upper thigh with a sharp object. If the reflex is intact the scrotum on that side is pulled upwards as the cremaster muscle contracts. Absence or reduction of both cremasteric reflexes indicates an upper *motor neuron lesion; absence of the reflex on one side suggests a lower motor neuron lesion at the level of the first lumbar spinal nerve.... cremasteric reflex

see Hoffmann’s sign.... finger-flexion reflex

a reflex action of the body that develops by five to six months and never disappears. If the body is held by the waist face down and lowered, the arms and legs extend automatically.... forward parachute reflex

(pharyngeal reflex) a normal reflex action caused by contraction of pharynx muscles when the soft palate or posterior pharynx is touched. The reflex is used to test the integrity of the *glossopharyngeal and *vagus nerves.... gag reflex

a wave of peristalsis produced in the colon by introducing food into a fasting stomach.... gastrocolic reflex

the relaxation of the *ileocaecal valve caused by the presence of food in the stomach.... gastroileac reflex

involuntary grasping in response to anything that touches the palm of the hand. This is a normal reflex in babies that is lost in early childhood. In adults it is a sign of damage to the *prefrontal lobes of the brain.... grasp reflex

the normal physiological reflex to breathe out when the breath is held in inspiration and to breathe in when it is held in exhalation. [H. E. Hering (1866–1948), German physiologist; J. Breuer (1842–1925), German physician]... hering–breuer reflex

an abnormal reflex elicited by lightly placing the index finger across the chin of the patient and tapping it with a tendon hammer while the jaw hangs loosely open. A brisk upward movement of the jaw indicates an upper *motor neuron disorder above the brainstem.... jaw-jerk reflex

a reflex seen in normal babies from three months until one year, when it disappears. If the baby is held horizontally, face down, it will straighten its legs and back and try to lift up its head. The presence of this reflex beyond one year may be suggestive of a developmental disorder.... landau reflex

a cough produced by irritating the larynx.... laryngeal reflex

see pupillary reflex.... light reflex

involuntary contraction of the stapedius and/or tensor tympani muscles in the middle ear in response to various stimuli. The stapedius contracts in response to sound (see stapedial reflex). The tensor tympani is thought to contract during chewing. The sound-evoked middle ear reflex can be detected using a *tympanometer.... middle ear reflex

(startle reflex) a primitive reflex seen in newborn babies in response to the stimulus of a sudden noise or movement: the baby will fling its arms and legs wide and will appear to stiffen; the arms and legs are then drawn back into flexion. The Moro reflex should disappear spontaneously by four months. Its presence beyond this age is suggestive of an underlying neurological disorder, such as cerebral palsy. [E. Moro (1874–1951), German paediatrician]... moro reflex

a reflex action of the intestine in which a physical stimulus causes the intestine to contract above and relax below the point of stimulation.... myenteric reflex

see stretch reflex.... myotatic reflex

(knee jerk) reflex contraction of the quadriceps (thigh) muscle so that the leg kicks, elicited in a patient sitting with one knee crossed over the other by sharply tapping the tendon of the muscle below the kneecap. The reflex is mediated through nerves emanating from the third and fourth lumbar spinal levels (see spinal nerves). This is a test of the connection between the sensory nerves attached to stretch receptors in the muscle, the spinal cord, and the motor neurons running from the cord to the thigh muscle, all of which are involved in the reflex. The patellar reflex is reduced or absent when there is disease or damage of the spinal cord at or below the level of the reflex and exaggerated in disorders above the level of the reflex.... patellar reflex

see gag reflex.... pharyngeal reflex

a reflex obtained by drawing a bluntly pointed object (such as a key) along the outer border of the sole of the foot from the heel to the little toe. The normal flexor response is a bunching and downward movement of the toes. An upward movement of the big toe is called an extensor response (or Babinski reflex or response). In all persons over the age of 18 months this is a sensitive indication of damage to the *pyramidal system in either the brain or spinal cord.... plantar reflex

(light reflex) the reflex change in the size of the pupil according to the amount of light entering the eye. Bright light reaching the retina stimulates nerves of the *parasympathetic nervous system, which cause the pupil to contract. In dim light the pupil opens, due to stimulation of the *sympathetic nervous system. See also iris.... pupillary reflex

flexion of the forearm (and sometimes also of the fingers) that occurs when the lower end of the radius is tapped. It is due to contraction of the brachioradialis muscle, which is stimulated by tapping its point of insertion in the radius.... radial reflex

the red area seen through the pupil as a result of the reflection of light from the retina. It is usually seen on *fundoscopy and sometimes in photographs taken using a flashlight.... red reflex

the nervous circuit involved in a *reflex, being at its simplest a sensory nerve with a receptor, linked at a synapse in the brain or spinal cord with a motor nerve, which supplies a muscle or gland (see illustration). In a simple reflex (such as the *patellar reflex) only two neurons may be involved, but in other reflexes there may be several *interneurons in the arc.... reflex arc

see complex regional pain syndrome.... reflex sympathetic dystrophy

a primitive reflex present in newborn babies: if the cheek is stroked near the mouth, the infant will turn its head to the same side to suckle.... rooting reflex

reflex contraction of the stapedius muscle in the middle ear, attached to the *stapes bone, in response to loud sounds. This protects the cochlea from noise damage by limiting the amount of sound that is transmitted via the stapes. The reflex can be measured using a *tympanometer.... stapedial reflex

the reflex maintenance of muscular tone for posture.... static reflex

a primitive reflex in newborn babies that should disappear by the age of two months. If the baby is held in a ‘walking’ position with the feet touching the ground, the feet move in a ‘stepping’ manner. Persistence of this reflex beyond two months is suggestive of *cerebral palsy.... stepping reflex

(myotatic reflex) the reflex contraction of a muscle in response to its being stretched.... stretch reflex

the closing of the eyelids when the supraorbital nerve is struck, due to contraction of the muscle surrounding the orbit (orbicularis oculi muscle).... supraorbital reflex