Examination of sensory nervous system

Practical medical physiology examination of sensory nervous system
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8- Examination of sensory nervous system
Sensory system is the afferent division of the peripheral nervous system
transmits information detected by sensory receptors that respond to specific
types of stimuli from the periphery to the central nervous system (CNS).
AIMS
To check the following sensations in the given subject:
1. Tactile sensibility—touch (fine and crude).
2. Pain sensation.
3. Temperature (hot and cold) sensation
3. Joint position sense and vibration sense
4. Stereognosis and graphysthesia.
Materials:
1- Piece of cotton.
2- Pin.
3- Cold and hot object.
4- Tuning fork.
5- Two blunt points.
Methods:
1- Light touch
* While the patient to close his eyes, use a piece of cotton wool and ask the
patient to say yes to each touch.
* Time the stimuli irregularly and make a dabbing rather than a
stroking or tickling stimulus.
* Compare each side for symmetry.
2- Pain
* it can be tested using pin placed gently to the skin. Explain and demonstrate
the test to the patient before starting.
* The eyes of subjects should be opened because closed eyes make the
patient anxious.
* pin should be moved from the proximal to the distal part testing different
dermatome at each time.Practical medical physiology examination of sensory nervous system
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3- Temperature: It can be tested by using cold and warm object (e.g. cold end
of tuning fork) and ask the subject to discriminate between the two. The
sensation of warm or cold is poorly localized. Subject s eyes must be closed.
4- Joint position: Ask subject to close his eyes and move joints start with distal
joints (interpharyngeal joints) in their range of movement and ask the patient
to detect the direction of movement (figure 8-1).
Figure 8-1:- joint position sense
5- Vibration: It is tested by using (125 Hz) tuning fork on bony prominences,
starting distally at tip of index finger then knuckles, snuffbox, elbow, rib,
sternum, etc. Ask subject to close eyes then ask them to identify the sensation.
6- Two point discrimination: The minimal distance by which two blunt touch
stimuli are perceived as separate is called the two point discrimination. Its
magnitude varies from place to place on the body. Ask subject whether one or
two points can be felt. Normally, it is about 2 mm on the fingertip and about 1
cm on the pulps of toes. It is about 6.5 cm on the back of the body.
7- stereognosis
With the subject’s eyes closed, he is given some article which is commonly
used, e.g. coins, pens, keys etc. in his hand and he is asked to name them.
Normally, he would be able to appreciate them with his eyes closed by their
size, weight, shape, texture, temperature, etc. Loss of this power is known as
astereognosis. The subject should use one hand only to feel the given object.Practical medical physiology examination of sensory nervous system
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8- graphesthesia
Use the blunt end of a pencil and trace letters or digits on the patient’s palm.
Ask the patient to identify the figure.
Clinical correlation:-
Paraesthesia= Tingling, or pins and needles Spontaneous or provoked Not
unduly unpleasant or painful
Dysaesthesia= Unpleasant paraesthesia
Hypoaesthesia= Reduced sensation to a normal stimulus
Analgesia= Numbness or loss of pain sensation
anasthesia= loss of sensation.
Hyperaesthesia= Increased sensitivity to a stimulus
Allodynia= Painful sensation resulting from a non-painful stimulus
Hyperalgesia= Increased sensitivity to a painful stimulus.
Dermatome:- area of skin supplied by single spinal cord segment or single
spinal nerve figure 8-2. Knowledge of different dermatomal distribution is
essential to detect the level of lesion.
Figure 8-2 dermatomal distribution of front and back