How are the spinal cord's gray and white matter organized and where are motor vs sensory neurons located?

• A. Gray matter forms an H-shaped core with dorsal sensory horns; ventral motor horns; White matter surrounds and contains ascending (sensory) and descending (motor) tracts
• B. Gray matter forms outer cortex; dorsal horns motor; ventral horns sensory; White matter lacks tracts
• C. Gray matter outer layer; dorsal horns motor; ventral horns sensory; White matter has no tracts
• D. Gray matter forms an O-shaped core; dorsal horns motor; ventral horns sensory; White matter carries only motor tracts

Answer: (A)

Spinal cord gray matter sits in the center as an H- or butterfly-shaped region that contains neuron cell bodies and synapses. The dorsal (posterior) horns handle sensory connections, while the ventral (anterior) horns house motor neurons that send impulses out to muscles. Surrounding this gray matter is the white matter, made of myelinated axons organized into tracts that carry information up and down the cord—ascending tracts convey sensory signals toward the brain and descending tracts carry motor commands from the brain down to the spinal nerves. Dorsal roots bring in sensory fibers (with the sensory neuron cell bodies located in the dorsal root ganglion), and ventral roots carry motor fibers out to muscles. This arrangement matches the description of gray matter being the central H-shaped region with dorsal sensory horns and ventral motor horns, and white matter surrounding it containing ascending and descending tracts.