Sensation
General considerations prior to evaluation:
- Almost the whole of the sensory examination is dependent on the
patient’s response (level of awareness, understanding of the test). Some
patients may give unreliable answers or have a cognitive impairment and
detailed sensory studies will be difficult or impossible.
- The sensory examination requires the greatest time, patience, caution and
tact.
- The normal pattern of distribution can vary (in not all subjects the ulnar
nerve supplies one and a half digit)
- Sensory levels on the trunk, almost indicative of a spinal cord disease, are
not horizontal but follow the oblique line of distribution of thoracic
dermatomes.
- The transition between an apparently anesthetic area, and an area with
normal cutaneuos perception appears often to be progressive and over a
finite distance (especially in peripheral neuropathies).
- Patients with hysterical anesthesia tend to complain, on the opposite of a
profound sensory loss with a very sharp transition from abnormal to normal.
- It is customary to first to go over sensation in a general way, in order to
map out the gross areas which need detailed study, and avoid consuming
unnecessary time when sensory changes are obviously not present.
- Quiet examination conditions are essential and repeated examinations are
advisable for accurate results.
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- Great care must be taken to avoid suggesting the response to the patient,
either by remarks of the examiner or by permitting the patient to observe the
stimulation. The eyes are best kept closed.
- Stimuli should at first progress from abnormal to normal areas not from
normal to abnormal, as the patient tends to interpret the last stimulus as that
of greatest intensity.
B. Sensory Evaluations:
Sensations may be divided in two categories; exteroceptive and
proprioceptive sensations.
 Exteroceptive sensations refer to those sensations that give the body
some information about external events: pain, temperature and light touch.
 Proprioceptive sensations refer to innate bodily sensations including deep
pain and the position of joints in space.
The results of the sensory examination should be studied in
comparison with the usual sensory distribution of various segments of the
spinal cord (Sensory Dermatomes) and the distribution of the superficial
nerves (refer to attached charts). The defects should be mapped out on a
sensory chart and determine whether the changes follow a peripheral nerve,
plexus or radicular distribution. One will also assess if the sensory changes
consistent with a lesion of the brain (i.e. in R. CVA it should affect the L.
side of the body) or if one type of sensation is preserved.
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Evaluation of exteroceptive sensations:
1. Superficial Pain:
By Pinprick Test for pain sensation with a sterile pin, comparing side with
side, proximal with distal, segment with segment. Never use a very sharp
needle, because it might draw blood, and could transmit infectious diseases.
Because of its sharpness and small area of stimulation it might miss pain
spots, giving rise to misinterpretation of sensory deficiency.
2. Temperature:
Test for temperature sensation with cold steel or with tubes filled with
water about 30C and 35 C or 50F (cold) and 110 F ( hot).The latter is
more accurate but less convenient. Borders of the thermal loss may be
determined by rolling the tube over the skin from affected to normal areas.
These borders will often coincide with the margins of pain sensibility. This
test is not routinely tested.
3. Light touch or tactile sensation:
Test for light touch sensation with cotton wool, applying it with dabs
rather than stroking movements. Cutaneous sensitivity to this stimulus is
variable. The calloused hands of a person accustomed to manual work are
likely to show a higher threshold to light touch than those with a normal
skin.
o Stimulation should not be applied too rapidly.
o An irregularity in rhythm in stimulation is to be adopted.
o A heavier stimulus will be applied over the palms of the hands or on the
feet.
o Compare symmetrical parts of the body.
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o Repeat the test.
o Make some trial tests where the therapist will do as if he touches the skin
while effectively he / she does not.
Evaluation of proprioceptive sensations:
1. Position of Joints in Space:
Test for this function by getting the patient to oppose the fingers of
the two hand with eyes closed or by putting one limb in a certain position
and getting him to make the same position with the other limb, with his eyes
closed.
2. Passive movements:
Ask the patient to close his eyes and identify the direction in which
you are moving the terminal phalanx of a finger or great toe (up or down).
Prior to this, demonstrate which movements you are going to test. Hold only
the sides of the digit being moved because the differential pressure provided
by your grip on top and underneath the digit will give more clues.
3. Deep pressure and deep pain:
Observe the patient’s reaction when you squeeze the Achilles tendon,
and assess the interval between the application of the painful stimulus and
the patient’s response, whether verbal or facial. If the fast conducting (tick)
fibers are severely damaged, the pain response may be delayed up to 2 or 3
sec.
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4. Vibration:
Introduce the patient to this test by placing the vibrating tuning fork
(128 HZ) on the chest wall and letting him feel the vibration. Then test by
placing it on toes and fingers, or medial malleolus but be sure that it is
vibration and not pressure that he/ she is feeling in each situation. To
compare the two sides, place the vibrating tuning fork on the extremity,
damp it gently with your fingers, and ask the patient to tell you as soon as he
no linger feels the vibration. Then quickly transfer the fork to the other side
and see if it is felt there. Perception of vibration tends to diminish with age;
its absence at the ankles in the elderly is not considered as significant.
With the possible exception of vibration, these sensations are
mediated by thick, rapidly conducting contra-lateral fibers passing upward in
the posterior columns with one relay, to the opposite ventro-posterior
thalamic nucleus and thence to the parietal cortex. In older patients,
symmetric diminution of the sense of vibration peripherally may not be
pathological.
Romberg’s test:
Get the patient to stand with his feet together for half a minute, then
ask him/ her to close his/ her eyes. A positive Romberg’s Test occurs when
the patient can stand with the eyes closed but falls when they are closed
(make sure you are there to catch him). It indicates a proprioceptive lesion
and is not a test for cerebellar function. With midline cerebellar disease, the
patient has difficulty in standing with the eyes open as well as them closed.
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Tests indicating cortical sensory loss:
Even though peripheral path ways and mechanisms may be normal,
correct interpretation of sensory stimuli requires that the parietal cortex be
functioning normally. If there is a possibility for cortical impairment,
examine stereognosis, tactile localization and sensory competition. Be aware
that in the presence of any major degree of sensory loss (light touch,
pinprick, deep pressure, etc.) test for cortical sensory loss may be invalid.
Stereognosis:
It is the ability to discriminate shape, size, weight, texture and form.
Test by tracing figures or numbers (graphesthesia) on the palm of the hand,
by getting the patient to identify coins or similar objects (key, paper clip,
eraser, etc) in his hand without seeing or hearing them. One can also test
two- point discrimination, using the blunted end of a compass placed on the
sides of the fingers or the toes. A separation of 5 mm on the fingertips is
usually taken as normal, while double or triple will be acceptable in the feet.
Other tests include the ability to discriminate textures as for cotton from silk,
a sheet from a blanket, paper from cardboard. These tests will be given to
the patient with his eyes closed.
Tactile localization:
Ask the patient to point out the place on the hands, arms and legs that
you touched, again with eyes closed.
Sensory competition:
It can be assessed if simultaneous bilateral touches are given, e.g. to
both hands, both sides of the face, and so on. Even though the subject may
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be able to perceive such stimuli given separately, if they are given both at
the same time one may be ignored, suggesting a contralateral cortical lesion.
This test can only be acceptable if peripheral sensation is normal.
Physiological considerations to somatic sensations:
Sensory stimuli such as touch, sound, light, cold, warmth are detected
by various sensory receptors giving input to the nervous system.
Sensory receptors:
There are basically five different types of sensory receptors:
1. Mechanoreceptors, which detect mechanical deformation of the receptor
itself or of cels adjacent to the receptors.
2. Thermoreceptors, which detect changes in temperature, some receptors
detecting cold and warmth.
3. Nociceptors, which detect pain, usually caused by physical damage or
chemical damage to the tissues.
4. Electromagnetic receptors, which detect light on the retina of the eye.
5. Chemoreceptors, which detect the taste in the mouth, smell in the nose,
oxygen level in the arterial blood, carbon dioxide concentration and other
factors linked to the chemistry of the body.
In the mechanoreceptors, amongst other receptors are Free Nerve
Endings. These are found in all parts of the body. A very large proportion of
these detect pain. However, other free nerve endings detect crude touch,
pressure, tickle, itch sensation and possibly warmth and cold.
Several other more complex receptors detect tissue information:
Merckel’s discs, tactile hairs, Pacinian corpuscles, Meissner’s corpuscles,
Krause’s corpuscles and Ruffini’s end-organs.
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In the skin, it is these receptors that detect the tactile sensations of
touch and pressure. In the deep tissues, they detect stretch, deep pressure, or
any type of tissue deformation- even the stretch of joint capsules and
ligaments to determine the movements of joints.
The Golgi tendon apparatus detects tension in the tendons, and the muscle
spindle detects the length of muscle.
Differential sensitivities:
Each type of receptor is very highly sensitive to the one type of
stimulus for which it is designed and yet it is almost non responsive to
normal intensities of the other types of sensory stimuli.
- The rods and cones of the eyes are highly responsive to light but are almost
non-responsive to heat, cold, pressure on the eyeballs, or chemical changes
in the blood.
- Pain receptors in the skin are almost never stimulated by usual touch or
pressure stimuli but do become highly active in the moment tactile stimuli
becomes severe enough to damage the tissues.
Adaptation of receptors:
A special characteristic of all sensory receptors is that they adapt
either partially or completely to their stimuli after one period of time. When
a continuous sensory stimulus is first applied, the receptor responds at a very
high impulse rate at first, then progressively less rapidly until finally, in
many instances, it no longer responds at all. Some receptors adapt more
rapidly than others while joint capsule and muscle spindle receptors adapt
very slowly. The chemical receptors never adapt completely while Pacinian
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corpuscles adapt to “extinction” within a few thousands or hundreds of
seconds.
Poorly (or very slowly) adapting receptors: are also called Tonic
receptors and continue to transmit the impulses to the brain for many
minutes or hours. These include the pain receptors, baroreceptors of the
arterial tree, chemoreceptors of the carotid or aortic bodies and some tactile
receptors. Because of our continually changing bodily state, the tonic
receptors almost never reach a state of complete adaptation.
Mechanisms by which receptors adapt:
In mechanoreceptors, (e.g. pacinian corpuscle) they are visco-elastic
structures, so that when a distorting force is suddenly applied to one side of
the corpuscle this distortion is transmitted to the viscous component of the
corpuscle directly to the same side of the central core fiber, thus eliciting a
receptor potential. However, within a few thousandths or hundredths of
seconds the fluid within the corpuscle redistributes so that the pressure
becomes essentially equal al through the corpuscle, with an even pressure on
all sides and the receptor potential is no longer elicited. Then when the
distorting force is removed from the corpuscle, the reverse events occur. The
sudden removal of the distortion from one side of the corpuscle allows rapid
expansion on that side, and a distortion of the central core fiber occurs once
more. This signals the onset of the compression and offset of the
compression.
The other process of adaptation of the Pacinian corpuscle results from
a process of accommodation of the nerve fiber itself. The tip of the nerve
fiber will be accommodated to the stimulus, perhaps as a result of
redistribution of ions across the nerve fiber membrane.
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Transmission of the mechano-receptive somatic sensory signals into the
central nervous system:
Either all or almost al sensory information from the somatic segments
of the body enters the spinal cord through the posterior roots. Immediately
after entering the cord, the nerve fibers separate into two major groups:
1) Dorsal lemniscal system (dorsal columns and spino-cervical tracts):
These are large myelinated nerve fibers (faster). They transmit
information that must be transmitted rapidly. It has the spino-cervical tracts
high degree of spatial orientation. The following sensations are transmitted
by this system:
- Touch sensation requiring a high degree of localization of the stimulus.
- Touch sensations requiring transmission of fine gradations of intensity.
- Phasic sensations, such as vibratory sensations.
- Sensations that signals movement against the skin.
- Positions sensations.
- Pressure sensations related to fine degrees of judgment of pressure
intensity.
2) Anterolateral spinothalamic system in the anterior and lateral columns.
This is constituated of smaller myelinated fibers (impulses are transmitted at
a lower speed). This system has a much smaller degree of spatial orientation.
The following sensations
are transmitted by the antero-lateral
spinothalamic system:
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Pain.
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Thermal sensations.
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Crude touch and pressure sensations capable of only crude localizing
ability on the surface of the body and having little capability for intensity
discrimination.
-
Tickle and itch sensations.
Transmission in the dorsal-lemniscal system:
Sensory signals are transmitted to the brain by way of two major athways:
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the dorsal column pathway
the spinocervical pathway.
Practical Laboratory
Tests and Measurements
Sem.2
Objectives:
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To be oriented to the various sensation testing procedures.
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To be able to apply the testing procedures and use the testing
equipment for sensation.
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To be able to compare normal with abnormal findings and record
these findings on documentation sheets.
Equipment:
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Pin prick test needle, hot and cold glass/ plastic tubes, vibration test
item, paper clip,eraser, key, cotton wool balls, alcohol swabs.
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Therapeutic or examination plinth.
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Exam. record sheet.
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Procedures of assesment:
Verify patient awareness and cooperation.
Orient patient to testing procedure and the possible sensations
he might feel.
Apply standard precautions and provide patient with privacy.
Undress the body parts to be tested.
Apply Pinprick Test
Apply Temperature sensation Test
Apply Light touch sensation Test
Apply Proprioceptive tests: - joint sensation
- position in space
- deep pressure
Apply Romberg’s Test
Apply Stereognosis Test - for graphesthesia
- for objects, forms recognition
Apply Vibration testing
Apply Tactile Localization Test
Asses Sensory Competition
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