In the pons at the level of the facial colliculus, the somatotopic arrangement of fibres within the medial lemniscus is:

• A Sacral fibres medial, cervical fibres lateral
• B Cervical fibres ventral, sacral fibres dorsal
• C Cervical fibres medial, sacral fibres lateral ✓
• D No somatotopy exists once fibres have crossed in the internal arcuate fibres

Explanation

After decussating through the internal arcuate fibres, the medial lemniscus lies ventral to the tegmentum. In the medulla the tract is oriented with sacral fibres ventral and cervical fibres dorsal. As it ascends into the pons it rotates roughly 90 degrees, so cervical (upper limb) fibres come to lie medially and sacral (lower limb) fibres laterally. Somatotopy is strictly maintained throughout the pathway, which rules out option D.

Reference: Snell's Clinical Neuroanatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.