NG, NC and NZ all extend internal arcuate fibers that cross at the GSD to form Contra ML. Which nuclei contribute?

NG, NC and NZ all extend internal arcuate fibers that cross at the GSD to form Contra ML. Which nuclei contribute?

• A. Nuclei Gracilis, Cuneatus, and Z
• B. Nuclei Gracilis and Cuneatus only
• C. Nucleus Z only
• D. Nuclei Gracilis, Nuclei Cuneatus, and Nuclei Proprius

Answer: (D)

Discriminative touch and proprioception travel in the dorsal column–medial lemniscus pathway. The second-order neurons are in the gracile nucleus (lower body) and the cuneate nucleus (upper body). Their axons form the internal arcuate fibers and decussate in the medulla, joining to become the contralateral medial lemniscus that ascends to the thalamus. In addition to the gracile and cuneate nuclei, the nucleus proprius contributes fibers to this same decussating system, so all three nuclei feed into the crossing that establishes the contralateral medial lemniscus. This explains why the best answer includes all three nuclei.

Discriminative touch and proprioception travel in the dorsal column–medial lemniscus pathway. The second-order neurons are in the gracile nucleus (lower body) and the cuneate nucleus (upper body). Their axons form the internal arcuate fibers and decussate in the medulla, joining to become the contralateral medial lemniscus that ascends to the thalamus. In addition to the gracile and cuneate nuclei, the nucleus proprius contributes fibers to this same decussating system, so all three nuclei feed into the crossing that establishes the contralateral medial lemniscus. This explains why the best answer includes all three nuclei.