The dorsal column–medial lemniscal pathway carries fine touch and proprioception. Neurons in the nucleus gracilis and nucleus cuneatus (second-order neurons) project to the ventral posterolateral (VPL) nucleus of the thalamus. At which level do these fibers cross the midline?

• A In the medulla oblongata (as internal arcuate fibers after synapse in gracilis/cuneatus nuclei) ✓
• B At the level of entry into the spinal cord (same spinal segment)
• C At the level of the pons in the medial lemniscus
• D In the thalamus before projecting to the somatosensory cortex

Explanation

First-order neurons in the dorsal column–medial lemniscal pathway ascend ipsilaterally in the posterior funiculus (gracile fasciculus from below T6; cuneate fasciculus from above T6) to synapse in the nucleus gracilis and cuneatus in the medulla. Second-order neurons then cross as internal arcuate fibers in the medulla and ascend contralaterally in the medial lemniscus to the VPL thalamus. This crossing pattern explains why medullary lesions cause contralateral loss of fine touch and proprioception below the level of the lesion — contrasted with ipsilateral loss from spinal cord lesions.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.