Which structure houses the first-order neuron of the DCML pathway?

• A. Dorsal horn
• B. Dorsal root ganglion
• C. Thalamus
• D. Ventral horn

Answer: (B)

For the DCML pathway that carries fine touch, vibration, and proprioception, the cell bodies of the first-order sensory neurons are located in the dorsal root ganglia adjacent to the spinal cord. These neurons have a peripheral process that innervates skin and proprioceptors and a central process that enters the spinal cord through the dorsal root and ascends in the dorsal columns. There, they synapse on second-order neurons in the nucleus gracilis and nucleus cuneatus after traveling up to the medulla. From that point, the pathway continues to the thalamus and then to the cortex. The dorsal horn and ventral horn are parts of spinal gray matter related to reflexes and motor control, not the location of the first-order sensory neuron cell bodies. The thalamus houses third-order neuron bodies, not first-order ones. So the dorsal root ganglion is the correct structure.