Dorsal root fibers (axons of primary afferent neurons) enter the spinal cord at the dorsolateral sulcus.
Entering fibers segregate: Non-myelinated fibers (conveying pain and temperature) collect laterally in the dorsolateral fasciculus. Larger fibers (conveying touch and kinesthesia) accumulate medially and form fasciculus gracilis (caudal half of the body) or fasciculus cuneatus (cranial half of the body).
Primary afferent axons entering spinal white matter divide into cranial and caudal branches. These branches give off collateral branches which enter gray matter to synapse on interneurons and projection neurons. Cranial branches of large primary afferent neurons (conveying touch and kinesthesia) continue on to the brain in fasciculus gracilis or fasciculus cuneatus.
