When does the DCML pathway cross over and synapse?

• A. When it reaches the medulla in the brain stem
• B. At the level of the spinal cord
• C. In the thalamus
• D. At the cerebellum

Answer: (A)

Crossing and first synapse occur in the medulla. In the dorsal column–medial lemniscus pathway, fibers carrying fine touch, vibration, and proprioception ascend ipsilaterally in the dorsal columns to the medullary nuclei—the nucleus gracilis for the lower body and the nucleus cuneatus for the upper body. There they synapse onto second-order neurons, which then cross to form the contralateral medial lemniscus that travels up to the thalamus and on to the cerebral cortex. So the key crossover point is the medulla, not the spinal cord, thalamus, or cerebellum.