5. Somatosensory Processes
Part 4 of 10
Patrick Dougherty, Ph.D.
(Content provided by Chiyeko Tsuchitani, Ph.D.).
Clincal Examples:
Peripheral Nervous System (continued)
The patient reports a loss of sensation along the lateral aspect of his left arm that extends down to include the thumb of his left hand.
Figure 5.12 |
Symptoms. The patient complains of a loss of sensation along the side of his left arm that extends down to include the thumb of his left hand (Figure 5.12). Physical examination determines that there are decreases in the abilities to detect vibration and position involving the left elbow and thumb and loss of touch and pain sensations along the lateral edge of the left arm down to the thumb. Touch, vibration, position, and pain sensations are normal for the rest of the body and face. You conclude that the somatosensory losses in his left arm involve
Pathway(s) Affected: You conclude that structures in the following somatosensory pathways (Figure 5.8) have been affected
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The results of testing somatosensory sensation for Example 2. A pin prick to the left thumb produces no perceived pain sensations; and a vibrating tuning fork in contact with the left arm or manipulating the left arm and thumb produce no vibration or proprioceptive sensations. Press Vibration and pain sensations are normal for the rest of the body. Press |
Figure 5.13 |
to view the course of action potentials generated in response to application of a vibrating tuning fork or a pin prick applied to the left thumb.
to view the course of action potentials generated in response to application of a vibrating tuning fork or a pin prick applied the left foot. Side & Level of Damage: As the sensory losses (Figure 5.13)
- are limited to the lateral aspect of the left arm and extended down to include the left thumb
- involve both somatosensory pathways
- involve a dermatomal pattern
- do not involve motor function
- damage may involve the fifth, sixth and seventh cervical posterior roots (Figure 5.11)
- symptoms are ipsilesional (i.e., involve the left posterior roots, Figure 5.14)
Figure 5.14 |
The fifth, sixth and seventh cervical posterior roots provide sensory innervation to the lateral edge of the arm. Compression of the posterior roots will prevent action potentials generated by somatic stimulation from reaching the spinal cord. |
Section of a Posterior Root results in the loss of all somatosensory modalities in a restricted area of the body defined by the root dermatome (Figure 5.11). Consequently, the damaged posterior root can be identified by the dermatomal pattern of sensory loss. Radiographic methods can be used to determine if the roots are being compressed by abnormalities in the vertebra.
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