Sensory Impairment


1. Fibres enter the root entry zone and pass up or down for several segments in Lissauer's tract before terminating in the dorsal aspect of the dorsal horn.

2. Second order neurons synapse locally, cross the midline and run up the spinothalamic tract and lateral lemniscus to terminate in the posterolateral nucleus of the thalamus. Throughout its course, the fibres lie in a somatotopic arrangement with sacral fibres outermost. In the brain stem the lateral lemniscus gives off collateral branches to the reticular formation, which projects widely to the cerebral cortex and limbic system and is joined by fibres from the contralateral nucleus and tract of the trigeminal nerve.

3. From the thalamus, third order neurons project to the parietal cortex.


1. Fibres enter in the root entry zone and run upwards in the dorsal columns to the lower medulla where they terminate in the nucleus gracilis and nucleus cuneatus.

2. Second order neurons decussate as the internal arcuate fibres and pass upwards in the medial lemniscus. Maintaining a somatotopic arrangement, they terminate in the ventral posterolateral thalamus.

3. Third order neurons arise in the thalamus and project to the parietal cortex.


Cerebellar dysfunction, page 176.

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