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Section II: Sensory Systems
5. Somatosensory Processes
Part 7 of 10

Patrick Dougherty, Ph.D.
(Content provided by Chiyeko Tsuchitani, Ph.D.).
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Clinical Examples:
Central Nervous System: The Spinal Cord (continued)

example 5

The patient suffers from loss of pain and temperature sensations from the left half of the body starting just below the left nipple and extending down to and including his left foot. He also exhibits loss of discriminative touch and proprioception in a corresponding area on the right side of his body.


Figure 5.23
 Symptoms: The patient exhibits a loss in voluntary control of the right leg. He also reports loss of sensation in both feet (Figure 5.23). Physical examination determines that there are losses of pain and temperature sensations involving the left half of his body starting just below the left nipple and extending down to include his left foot. There are also loss of vibration and position sensations and poor localization of tactile stimuli on the right side of his body starting just below the right nipple and extending down to include his right foot. Touch, vibration, position and pain sensations are normal for the rest of the body and face. The Romberg test is positive (i.e., The patient has difficulty standing upright with his feet together and his eyes closed).

You conclude that the somatosensory losses in his body (Figure 5.24) involve a "dissociate anesthesia"; that is, loss of

  • pain and temperature sensations on the left lower body
  • discriminative touch and proprioception on the right lower body
The patient exhibits "dissociate anesthesia"; i.e., a loss of discriminative touch and proprioception on one side of the body and a loss of pain on the opposite side of the body.

Figure 5.24

Pathway(s) Affected: You conclude that structures in the following somatosensory pathways (Figure 5.25) may have been affected

  • the spinothalamic pathways
  • the medial lemniscal pathway

Figure 5.25


Neurons in the medial lemniscal pathway (MLP) process discriminative touch and proprioception from the body, whereas those in the neospinothalamic pathway (NSTP) process sharp pain and temperature information from the body. The right half of the spinal cord contains the uncrossed 1° afferents of the medial lemniscal pathway, which are in the right posterior funiculus, and the crossed 2° afferents of the neospinothalamic pathway, which are in the right lateral funiculus.

Side & Level of Damage: Motor functions are involved and the sensory losses (Figure 5.26)

  • do not involve the face
  • involve both the spinothalamic and medial lemniscal pathways
  • start at the nipples and extend to the feet
  • are different for each side of the body (i.e., pain on the left and vibration on the right)
Figure 5.26

The results of testing somatosensory sensation for Example 5.

Neither a vibrating tuning fork applied to the right foot nor a pin prick applied to the left foot result in the appropriate sensations. Press foot to view the course of action potentials generated in response to the tuning fork on the right foot and a pin prick to the left foot.

Vibration and pain sensations are normal for the rest of the body. Press hand to view the course of action potentials generated in response to the tuning fork on the right hand and a pin prick to the left hand.

 

So, you conclude that

  • damage involves one half of the spinal cord (i.e., hemisection of the spinal cord, Figure 5.27)
  • the fifth thoracic segment of the spinal cord may be involved (Figure 5.11)
  • the symptoms are bilateral but involve damage to the right half of the spinal cord (i.e., The symptoms are contralesional (on the left side) for pain and ipsilesional (on the right side) for vibration with a hemisection of the (right) spinal cord, Figure 5.27)

Figure 5.27
 Damage of the right half of the spinal cord at upper thoracic levels (T5) produces the Brown-Sequard syndrome that starts below the nipples and extends down to include the feet. The symptoms are bilateral - with discriminative touch and proprioception lost on the ipsilesional side and pain and temperature affected on the contralesional side.

Hemisection of the Spinal Cord. The symptoms resulting from hemisection of the spinal cord (i.e., damage to the right or left half of the spinal cord) are collectively called the Brown-Sequard syndrome (Figure 5.27). There are both motor and sensory losses: for now learn that the motor losses involve weakness, loss of fine motor control, and abnormal reflexes (which are characteristic of “upper motor” neuron damage) on the ipsilesional side starting at the level of the lesion and extending down the body. For example, if the right spinal cord is sectioned, say at T5, the motor effect is on the right side starting at the chest and extending down to and including the right leg and foot. Because spinal cord hemisection interrupts both the posterior column and spinothalamic tracts, there will be sensory losses that are bilateral: ipsilesional for the posterior column (discriminative touch and proprioception) and contralesional for the spinothalamic tracts (pain and temperature). As the sensory losses in each half of the body differ, they are sometimes referred to as “dissociate anesthesia.”

Clinical Examples: Example 1, the periperal nervous system Clinical Examples: Example 2, the periperal nervous system Clinical Examples: Example 3, the spinal cord Clinical Examples: Example 4, the spinal cord Clinical Examples: Example 5, the spinal cord Clinical Examples: Example 6, the spinal cord Clinical Examples: Example 7, the brain Clinical Examples: Example 8, the cortex

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