sensory system

2. The examination of the sensory system includes the
testing of various forms of sensations as described
under:
 Tactile sensibility, i.e. sensation of light touch,
pressure(crude touch), tactile localization and
discrimination
 Pain
 Temperature
 Sense of position
 Vibration sense
 Recognition of the size, shape, weight and form of
objects
 Presence of any abnormal sensations

3.  A dermatome is an
area of skin that is
mainly supplied by
afferent nerve fibers
from a single dorsal
root of spinal nerve
which forms a part of a
spinal nerve.
 Symptoms that follow a
dermatome may
indicate a pathology
that involves the
related nerve root.

4.  Before starting the examination, explain the nature of
the test to be performed on the subject to get his full
cooperation.
 Ask the subject to close his eyes or turn the face to
the other side and test the different forms of
sensations.
 Always compare corresponding points on both sides
of the body.

5. 1. Light Touch: Touch with low threshold.
(a) Use a wisp of cotton wool and test from different
parts of the body. Ask the subject to say 'yes' every
time he feels a touch.

6. Crude touch(Pressure sense): Pressure is
sustained touch sensation. Repeat the above test
using a blunt object or finger.
Note any disturbance in its perception over the
different portions on the body.

7.  Complete absence of touch
sensibility is called anaesthesia;
 Its partial loss, called
Hypoaesthesia
 Exaggerated (increased) sensibility
to touch, is called Hyperaesthesia.

8. Tactile localization: The ability to tell
precisely the portion of body part
touched.
Tell subject to close his eyes.
Touch different parts of the skin with pen
and tell subject to locate it.
See wether the point is same or different.

9. Tactile discrimination: The ability to distinguish
between two adjacent touch stimuli to the skin.
The tactile discrimination is tested by the use of
compass aesthesiometer The two limbs of the
instrument are separated and the subject's skin is
touched by both points. Ask whether he is being
touched with one or both the points.

10.  Normally, 2-3 mm of separation of the points can be
recognized as two separate stimuli on fingertips, whereas
two points on the back must be separated by 65 mm or
more before they can be distinguished as separate points.
 It is greater on the thumb, fingers and lips where the
sensory units are small and overlap considerably, than on
the back where the sensory units are large and widely
spaced

11. Pain may be produced either by a cutaneous stimulus
such as the prick of a pin(superficial pain) or by
pressure on deeper structure, such as muscles or bone
(deep or pressure pain).
1.Superficial pain. Use the point of an ordinary
domestic pin and using the same technique as used
for touch
Tell subject to say ‘yes’ when he feels pain.

12. 2.Deep or pressure pain. This is tested by squeezing
the muscle or the tendoachilles;
Or with an algometer, carefully press on the surface of
the body and note the minimum pressure required to
produce pain.
this sensation is particularly disturbed in tabes dorsalis.

13. • Analgesia=absenceof painsensation
• Hypoalgesia=decreased
• Hyperalgesia=increased
• The absence of pain sensibility is called Analgesia.
Its partial loss, the Hypoalgesia,and an increased
(exaggerated) response, the Hyperalgesia.
Therefore, even a mild stimulus causes an
unnatural degree of painful sensation.
• Hyperalgesia occurs in tabes dorsalis and thalamic
lesions (thalamic pain).

14. This is tested by using test tubes containing warm and
cold water. The part to be tested is touched with each
in turn, and the person says whether each tube feels
hot or cold.

15. The extent and direction of joint movements is
closely related to the sense of position that can be
examined accurately with the person's eyes closed.
1.Ask the subject to look away. Explain the
procedure to the subject, then move his finger (or
toe or elbow) up or down and ask him to tell you
which way it has been moved. He should be able
to recognize the movements of only a few degrees
(less than 10°) at all joints which include knee,
ankle, elbow, wrist, finger and toes.
.

16.  2. Hold one of the subject's limbs and move it in
various directions through the air, finally leaving in
some definite position, say semi flexed or extended.
Then ask him to put the corresponding limb in a
similar position

17. 1. Supply proper instructions to the subject.
2. Make the tuning fork vibrate by hitting the blades of
the fork against palm or thigh.
3.Place the foot of the vibrating tuning fork on the
surface of the body, especially on a bony prominence
(like lower end of tibia, styloid process of the radius
etc).
4. Ask the subject whether he feels the vibration.
5. Immediately place the tuning fork on the
corresponding bony prominence of your body and
note whether you can still perceive the vibration.

18. 3. Vibration sensibility is lost in tabes dorsalis,
peripheral neuropathies, such as diabetes, vitamin
deficiencies and in posterior column disorders.
4. There is often some loss of vibration sense in the feet
and legs in old age.

19. Sense of Stereognosis:
The ability to recognize familiar objects, such as
coins, a pencil, pen, scissors, etc. by handling them
without looking at them, is called stereognosis. It
depends upon intact touch-pressure sensation.
These sensations can be tested most accurately in the
hands with the eyes closed:
To test the recognition of shape , familiar objects are placed in
the hand, and the subject is asked to identify them or describe
their forms.

20. Loss of stereognosis (astereognosis) is an early sign of
damage to the parietal lobe when touch-pressure
sensation is normal.

21.  The presence of abnormal sensations over the body is
referred to as paraesthesias. This consists of various
sensations experienced by the person in the absence
of any outside stimulus. For example, feeling of
‘pins and needles’, of numbness, of pressure, of
tightness, of itching or a feeling as if an insect is
crawling over the body (formication). This phenomen
is called sensory inattention and is sometimes found
in persons with parietal lobe lesions.