dorsal root

Embryologically and functionally, the dorsal root arises from the dorsal (posterior) aspect of the spinal cord and contains only afferent (sensory) fibers that transmit information such as pain, temperature, touch, proprioception, and vibration from peripheral receptors to the central nervous system. The pseudounipolar sensory neurons whose axons form the dorsal root have their cell bodies located in the dorsal root ganglion (DRG), situated within or just outside the intervertebral foramen. Central processes of these neurons enter the spinal cord at the dorsal horn, where they synapse (directly or via interneurons) and give rise to ascending sensory pathways (dorsal columns for fine touch/proprioception, or cross and ascend via the spinothalamic tract for pain/temperature). The dorsal root combines with the ventral root (motor, efferent fibers from anterior horn cells) distal to the DRG to form the mixed spinal nerve, which then exits through the intervertebral foramen. Clinically, lesions or compression of the dorsal root (e.g., due to herniated disc, degenerative changes, or herpes zoster reactivation in the DRG) cause radicular pain, sensory deficits, and diminished reflexes in a dermatomal distribution without motor weakness, distinguishing it from ventral root lesions. Tabes dorsalis (tertiary syphilis) classically damages the dorsal roots and dorsal columns, causing loss of proprioception, sensory ataxia, and Argyll Robertson pupils. Herpes zoster reactivates in the dorsal root ganglia, producing dermatomal vesicular rash and neuropathic pain (postherpetic neuralgia). Understanding dorsal root anatomy is essential for localizing lesions in radiculopathies and interpreting dermatomal sensory loss patterns.