A knife wound at the cervicomedullary junction severs the pyramids just as they cross the midline. At which anatomical site does this crossing occur?
- A Ventral tegmental decussation of the midbrain
- B Sensory decussation of the caudal medulla
- C Decussation of the pyramids at the lower medulla ✓
- D Anterior white commissure of the upper cervical cord
Correct answer: C. Decussation of the pyramids at the lower medulla
Explanation
About 75 to 90 percent of corticospinal fibres cross in the decussation of the pyramids at the junction of medulla and spinal cord, forming the lateral corticospinal tract. The sensory decussation carries internal arcuate fibres from the dorsal column nuclei, not motor fibres. The ventral tegmental decussation carries rubrospinal fibres, and the anterior white commissure carries spinothalamic fibres.
Reference: Gray's Anatomy, 42nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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