Download Examination of sensory physiology Obgective:To determine the

Examination of sensory physiology
Obgective:To determine the sensory lesion:
Introduction:
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Fibers mediating fine touch and proprioception (joint
position, vibration and two point discrimination
sensations ) ascend in the dorsal column to medulla
oblongata, where they synapse in the gracile and cuneate
nuclei. The second order neurons from these nuclei cross
the midline and ascend in the medial lemniscus to nucleus
of thalamus . this is called dorsal column pathway . other
touch fibers (crud) with those mediating temperature and
pain synapse on neuron in the dorsal horn. The second
order neurons cross the midline and ascend in the ventral
and lateral spinal cord (spinothalamic tract) then run to
the thalamus. From thalamus third order neurons of all
sensory modalities transmit to cerebral cortex.
Pathway of sensory nervous system
There are six main sensory modalities that can be tested:
1.touch (fine and crud) sensation
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2.temperature (cold and warm)
3.pain sensation
4.joint position sensation
5.two point discrimination
6.vibration sensation
Other sensations are stereognosis (recognition of the size ,shape) and
weight perception. Fingertips are very sensitive to light touch and
discrimination.
The fine touch and proprioception sensory modalities enter the central
nervous system via large myelinated peripheral nerve fibers through
posterior column pathway ,while nociceptive (pain and temperature )
modalities enter via small, myelinated OR unmyelinated fibers such as
pain and temperature through spinothalamic pathway
Term in sensation :
1.Hyposthesia :decreased sensation.
2.Hypersthesia:Increased sensation ,subject feels a touch as pricking or
burning sensation .
3.Anasthesia:The sensation is completely abolished.
4.Analgesia:Loss sensation of pain.
5.parasthesia:Tingling sensation.
Materials
1.piece of cotton or cotton wool. .
2.pinprick .
3.cold and hot object.
4.tuning fork.
5.two blunt points.
Methods:
1Touch:it can be tested by using pin prick or cotton wool . it is
transmitted in both pathways (dorsal column & spinothalamic) Subject's
eyes must be closed
2.Pain:it can tested by using pinprick. The eyes of subjects should be
opened because closed eyes leads to anxious or hart them . the
examination must be no more then 15 second and avoid repeating the
test more then once because this causes fatigue . if the skin of palm is
thick ,test the sides.
3.Temperature: it can be tested by using cold and warm object (e.g. cold
end of tuning fork) and ask the subjects to discriminate between the two
The sensation warm or cold is
proorly localized .Subject s eyes must be closed.
4-Vibration:It is tested by using (125Hz) tuning fork on bony
prominences starting distally at tip of index finger then elbow ,knee, leg,
rib ,sternum, etc, Ask subject to close eyes then ask them to identify
the sensation.
5-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.