Summarize the following text to main points and sub-points and make detailed explain for them:

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Lab (10): Somatosensory functions 
(Physiology) 
ILOs: To 
C. 9 Perform an examination of different types of sensation. 
C. 10 Test fine touch, crude touch, proprioceptive, stereognosis and pain sensation.  
NARS: (1.8; 1.10). 
 
EXAMINATION OF THE SENSORY SYSTEM 
Sensation depends on impulses that occur as a result of stimulation of receptors located in the 
skin, muscles, tendons, and so on, and are sent along nerve fibers to the central nervous system 
(brain and spinal cord). The sensory exam is used to determine areas of abnormal sensation, 
the quality and type of sensation impairment, and the degree and extent of tissue involvement.  
A sensory exam involves evaluating different types of sensation, including pain, temperature, 
pressure, and position and compares the response in different parts or opposite sides of the 
body. For examination of the sensory system to have diagnostic or localization value, it must 
be done properly.  
Some knowledge of the anatomical representation of the various spinal segments on the skin is 
required landmarks worth remembering to include: 
Face 
5th cranial nerve 
Neck 
C2,3,4 
Arms 
C5-T3 
Trunk 
T4-8 
Abdomen 
T8-12 
Genitalia 
S2,3 
Leg, front 
L2-5 
Leg, back 
S1-3 
Perianal region 
S4 
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For each sensation the student should know: the receptors involved, and the peripheral and 
central pathways, i.e. the chains of neurons which carry the sensory signals from the receptors to 
the thalamus, and thence to the somatic sensory cortex. 
APPERATUS: 
The following equipment are necessary: 
- Cotton. 
- A long pin which can give a steady even at stimulus. 
- A test tube of warm and cold water. 
- A tuning fork which vibrates at 128c.p.s. 
- A blunt pointed divider (compass) 
PROCEDUER: 
The sensations to be examined may be divided into: 
1. CUTANEOUS SENSATIONS: which give the body information about external events such 
as:  
- Temperature 
- Pain 
- Touch  
▪ Crude touch 
▪ Fine touch  
• Tactile localization 
• Tactile discrimination 
2. DEEP SENSATION: which refer to innate bodily sensation such as: 
- Sense of movement. 
- Sense of position. 
- Sense of muscle tension. 
- Sense of deep pressure. 
3. COMBINED SENSATION: 
- Stereognosis. 
- Vibration sense. 
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TESTS FOR CUTANOUS SENSATIONS 
A) Examination for spinothalamic sensation 
1. TEST FOR PAIN SENSATION:  
With the eye closed, cutaneous pain is tested with a pin side with side, proximal with distal, 
segment with segment. Identify and map out areas of sensory impairment. Never use a very sharp 
needle, because this might draw blood and never reuse it as it could transmit hepatitis.  
a.  Pricking the skin with a pin at different pressures (Figure10-1). 
b.  Deep pain can be measured by observing the pressure which produces pain. 
c. Quantitatively pain can be measured by observing the amount of radiant heat which evokes 
pain.  
  
 
 
Figure 10-1 Test for pain sensation 
Figure 10-2 Test for temperature sensation 
2- TEST FOR TEMPERATURE SENSATION:  
Ask the patient to close his eyes and to say if he is being touched with the test tube containing 
hot (45C) or cold (30C) water. Since both pain and temperature sensations are carried in the 
lateral spinothalamic tract, temperature sensation is not routinely tested but is additive to the 
demonstration o an area of analgesia (Figure10-2). 
3- TEST FOR CRUDE TOUCH:  
With the patients eyes closed touch the skin with a wisp of cotton wool, asking the patient to say 
“Yes” only if he feels he is touched. If the sensation in any area of the body is found dull, its 
extent should be defined and recorded. If there is impairment of touch sensation in normally 
sensitive areas such as the hands or limbs, the patient can usually define the area himself, and 
you have only to confirm and record (Figure10-3). 
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Figure 10-3 Tests for light touch 
Figure 10-.4 Tests for tactile discrimination 
4. DEEP (PRESSUE) TOUCH:  
It is tested by applying weak pressure on the part to be tested. Accurately tactile sensations can 
be tested by Von Frey's hairs: These consist of hairs of different lengths and diameters mounted 
on a wooden handle and calibrated according to the force in gram needed to bend them.  
B) Examination for Dorsal column sensation 
1) TACTILE LOCALIZATION:  
It is the ability to detect the locality to which the stimulus is applied. Ask the patient to close his 
eyes and point out the place where he has been touched.  
2) TACTILE DISCRIMINATION:  
It is the ability to discriminate between two stimuli applied simultaneously at two separate points 
of contact. It can be investigated by allowing the two blunted points of a compass to 
simultaneously touch the skin. At first the 2 points are wide apart. Then, the distance between 
them is decreased in steps. Normally the 2 points are felt as 2 distinct stimuli, provided that the 
distance between them exceeds certain minimal value. The acuity of tactile discrimination is 
determined by the number of the receptors in the examined area and the extent of its 
representation in the cerebral cortex. The greater the number of the receptors and the larger the 
area of the cortical representation, the shorter will be minimal distance for tactile discrimination 
and vice versa. Tactile discrimination is more marked in certain areas such as fingers, lips and 
tongue than other areas e.g. back, shoulder and thigh (Figure 10-4). 
 
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3) DEEP SENSATIONS:  
a. SENSE OF DEEP PRESSURE:  
It is tested by applying firm pressure to the muscle. It can be tested quantitatively by placing 
different weights on the supported hand. The person with his eyes closed can detect the 
differences in the weights (Figure10.5). 
 
 
Figure 10-5 Test for deep pressure sensation 
Figure 10-6 Test for position sense. 
 
 
Figure 10-7 Test for passive movement sensation. 
Figure 10-8 Test for muscle tension. 
b. SENSE OF POSITION:  
This can be tested by placing one of the limbs of the person in an abnormal position. The person 
with his eyes closed is asked to place the other limb in a similar position (Figure10-6).  
c. SENSE OF PASSIVE MOVEMENT: 
 
The finger of the person is moved up or down. The person with his eyes closed can detect the 
extent and the direction of the passive movement imposed on a single joint (Figure10-7). 
d. SENSE OF MUSCLE TENSION:  
The person is asked to lift different weights. Then he is asked to detect the differences in the 
weights lifted (Fig.10-8). 
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e. VIBRATION SENSE:  
This can be evoked by placing the base of a vibrating tuning fork (128 Hz) on the skin covering 
superficial bone (medial malleoli, mastoid process and spinal processes of the vertebrae). 
Frequencies higher than this may not be well appreciated by some normal persons (Figure10-9).  
 
 
Figure 10-9 Test for vibration sense. 
Figure 10-10 Test for stereognosis. 
f. STERIOGNOSIS: 
 
It is the ability to discriminate shape, size, weight, texture and form of objects without use 
of visual sensation. Tested by placing familiar objects in the patients hand while his eyes are 
closed and asked him to identify these objects by touching. e.g. coins, pens, keys are good test 
objects (Figure 10-10). 
NORMAL: 
• 
Light touch, pinprick, vibration and position sense are intact throughout 
ABNORMAL FINDING OF SENSATION 
If the screening test is abnormal you need to perform detailed evaluation to document site, 
distribution and exactly which sensation is impaired. This information is helpful in determining 
the etiology for the abnormality.  
• 
Loss of all sensations in a symmetrical and distal distribution. Glove and stocking type 
(Peripheral neuropathy).  
• 
Loss of all sensation in the distribution of one peripheral nerve (Mononeuropathy).  
• 
Loss of all sensation in a dermatome (root lesion).  
• 
Loss of pain and temperature with preservation of other senses. Central cord 
(Syringomyelia).  
• 
Loss of position and vibration (Dorsal column or its afferent nerves).  
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• 
Ipsilateral loss of position and vibration and contralateral loss of pain and 
temperature below the level of lesion. Transection of half of spinal cord (Brown-Sequard 
syndrome).  
• 
Bilateral loss of all sensations below a level (Transection of spinal cord).  
• 
Loss of all sensations on the opposite side of lesion Hemianesthesia (Thalamic lesion).  
• 
Loss of cortical sensation on opposite side with some decrease in other sensations. 
(Parietal cortex lesion)  
o Check for double simultaneous stimulation  
o Graphesthesia  
o Stereognosis  
• 
Vibration sense is lost in peripheral neuropathies (diabetes mellitus), tabes dorsalis, and 
dorsal column disease. 
• 
Hypoalgesia means decrease of cutaneous sensations, especially pain sensation. The term 
analgesia refers to loss of pain sensation. Hyperalgesia is exaggerated sensitivity to pain 
so that a mild stimulus that was painless before now evokes pain. Hyperesthesia refers 
to increased sensitivity to 

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