Final answer:
A spinal cord hemisection results in hemiplegia on the damaged side, where pain can be felt but fine touch and proprioceptive sensations are lost. The unaffected side loses pain perception, but retains fine touch and proprioceptive sensations. This difference in sensory discrimination helps pinpoint the level of spinal trauma.
Step-by-step explanation:
When damage to one side of the spine results in differential losses on ipsilateral versus contralateral sides, sensory discrimination can be used to assess the level of spinal cord damage. In the event of a spinal cord hemisection, motor and sensory functions are affected differently on either side of the body. On the side of the body where the spinal cord is damaged (ipsilateral), a patient may experience hemiplegia, wherein there would be paralysis and loss of proprioceptive sensations and fine touch.
However, the patient will still feel pain due to the spinothalamic tract crossing over to the opposite side (contralateral) and ascending to the brain. On the opposite side (contralateral) of the injury, fine touch and proprioceptive sensations will be intact because the dorsal column pathways ascend ipsilaterally and will not be affected by the hemisection, while the perception of pain is lost.
These sensory deficits are crucial for localizing the injury level, and a simple test with a cotton-tipped applicator can be informative. Such an evaluation can be particularly useful when imaging technology like magnetic resonance imaging (MRI) or computed tomography (CT) scanning is not immediately available, such as at the scene of an accident.