Monday, June 6, 2011

Corneal Reflex

Corneal reflex is also known as blink reflex. The condition may be described as the involuntary blinking of the eyelids.

This is generally induced by either touching or because of any stimulation caused as a result of foreign bodies. The condition may also be caused by stimulation that may be caused as a result of bright light. The condition has been also found to occur when a human being is exposed to sounds greater than 40-60dB.The mediation of the corneal eyelid reflex is through nasociliary branch of the ophthalmic branch or through the 7th cranial nerve. The mediation may also be due to medullary center. It is possible to either reduce or completely eliminate this reflex by making use of the contact lenses. Some of the neurological examinations can be helpful in diagnosing this type of reflex. This reflex is generally not seen in infants who are less than 8 months of age. When the affected eye is stimulated, then the damage to the ophthalmic branch of the 5th cranial nerve can be responsible for ensuring that the reflex is absent. Under most of the circumstances, a consensual response is found to occur upon the stimulation of the cornea. In this case, both the eyelids are generally closing.

Sunday, June 5, 2011

Sensory Function in Children From Birth

Such functions include Vision, hearing, smell, taste and touch. How are they peculiar to a newborn or a child?

At birth, the eye is structurally incomplete. The fovea centralis is not yet completely differentiated from the macula. The ciliary muscles are also immature, limiting the ability of the eyes to accommodate and fix on an object. However, the pupils react to light, the blink reflex is responsive to a minimal stimulus, and the corneal reflex is activated by a light touch. Tear glands usually do not begin to function until the neonate is 2 to 4 weeks of age.

The newborn has the ability to momentarily fix on a bright or moving object that is within 20cm (8 inches) and in the midline of movement is greater during the first hour of life than during the succeeding several days. Although Visual acuity is difficult to measure, it has been found that a newborn can respond to orthokinetic stripes that are comparable to 20/50 vision.

Once the amniotic fluid has drained from the ears, the infant probably has auditory acuity similar to that of an adult. The neonate is able to detect a loud sound of about 90 decibels and reacts with a startle reflex. The newborn's response to sounds of low frequency and high frequency differs; the former, such as the sound of a heartbeat, metronome, or lullaby, tends to decrease an infant's motor activity and crying, whereas the latter elicits an alerting reaction.

There also seems to be an early sensitivity to the sound of human voices, although not to specific speech sounds. One study found that infants younger than 3 days of age can discriminate the mother's voice from that of other females. As early as age 2 weeks the neonate may stop crying to listen to the sound of a voice. The cortical activity associated with hearing or with any other sense is still incomplete at this stage because of the immature myelination of the various neural pathways beyond the midbrain, This lack of cortical integration is responsible for the infant's response to sound.

The internal and middle ears are larger at birth, but the external canal is small. The mastoid process and the bony part of the external canal have not yer developed. Consequently, the tympanic membrane and facial nerve are very close to the surface and can be easily damaged.

Limited research has been done on the newborn's ability to smell, However, it is known that newborns will react to strong odors such as alcohol or vinegar by turning their heads away. Recent studies have demonstrated that breast-fed infants are able to smell breast milk and will cry to their mothers when the breasts are engorged and leaking. Infants also have the ability to differentiate the breast milk from their mother or from other females by the smell.

The newborn has the ability to distinguish between tastes. Various types of solutions elicit differing gustofacial reflexes. A tasteless solution elicits no facial expression, a sweet solution elicits an eager suck and a look of satisfaction, a sour solution causes the usual expression. During early childhood the taste buds are distributed mostly on the tip of the tongue.

At birth, the infant is able to perceive tactile sensation in any part of the body, although the face (especially the mouth), hands, and soles of the feet seems to be most sensitive. There is increasing documentation that touches and motion are essential to normal growth and development, Gentle patting of the back or rubbing of the abdomen usually elicits a calming response from the infant. However, painful stimuli, such as a pinprick, will elicit an angry, upsetting response.

These peculiarities are very essential in observing the healthy state of a newborn or infant.