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Transcript
Examination of sensory physiology Obgective:To determine the sensory lesion: Introduction: . 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 \ 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.