reflexes

MOTOR FUNCTION

REFLEXES
Introduction and principle
A reflex is an involuntary event that we can’t control . It requires reflex arc that consist of a receptor, afferent (sensory) fiber, integrating center, efferent (motor or sensory) fiber, and effecter organ (muscle or gland). To initiate a reflex we should have (apply) a stimulus .
Reflexes can be classified into deep, superficial, and eye reflexes. reflexes can be monosynaptic as in stretch reflexes, or polysynaptic as in superficial reflexes. Deep reflexes arc also called jerk, myotatic or stretch reflexes , and are triggered by a sharp tap on an appropriate muscle or tendon. Superficial reflexes also referred to as coetaneous reflexes, and are caused by stroking or scratching a part of the skin surface or mucous membrane.

Objectives

To test the integrity of the different components of the reflex arc .

Materials and instruments

neurological hammer.

Procedure

1-Stretch reflexes e.g . knee jerk, ankle jerk , biceps jerk, triceps jerk .These reflexes are elicited by tapping briskly on a tendon which suddenly stretchs a muscle, resulting in its contraction . The muscle being tested must be relaxed and the same stimulus intensity should be applied to both sides. The response will be in the form of contraction of the stretched muscle that will eventually produces movement of the attached limb .



2-Superficial reflexes.e.g plantar reflex .Assessment of the plantar (the babinski response) is of great clinical importance.
The outer edge of the sole of the foot is stimulated by gently scratching a key or a stick along it from the heel towards the little toe and then medially across the metatarsus .
a-flexor plantar response: i.e Babinski sign negative.In the healty adult response plantar flexion and adduction of toes particullarly of the big toe. (Fig.2)
b-extensor plantar reflex i.e Babinski sign positive.An abnormality in the plantar response was first described by Babinski.Dorsiflexion (extension ) of the big toe and fanning of the other toes in response to a light stimulation of the outer margin of the sole of the foot.Children under one and half years of age exhibit the sign because of an incomplete development of the nervous system (corticospinal tract) at this time . Presence of reflex after one and half years of age in conditions include interruption of corticospinal tract development and lesion in the upper corticospinal tract





stretch reflexes and superficial reflexes are used in testing the integrity of the C.N.S as well as the brain stem.

Results

Apart from the normal responses , there might be exaggerated (hyper or brisk) reflexes or sometimes sluggish (under active or depressed) reflexes . Each result should be taking into consideration the history and other clinical findings .

Discussion

What are the conditions causing hyperreflexia ?
In which conditions there is diminished or absent reflexes ?