Dorsal roots are bundles of nerve fibers that emerge from the spinal cord as part of the peripheral nervous system. They connect the outer regions of the body to the central nervous system, relaying sensory information from tissues and organs. These roots, which help form the spinal nerves, are arranged in pairs at different levels of the spinal cord.
Anatomical Location and Structure
Dorsal roots emerge from the posterior (back) side of the spinal cord. Each root is composed of smaller nerve rootlets that combine as they extend away from the cord. A feature of each dorsal root is a swelling known as the dorsal root ganglion (DRG), or spinal ganglion. This cluster of nerve cell bodies is located within the intervertebral foramen, the bony openings between vertebrae.
The DRG contains the cell bodies of sensory neurons. These neurons are pseudounipolar, meaning each has a single axon that splits into two branches. One branch extends toward the periphery to detect sensory stimuli, while the other travels into the spinal cord. Just outside the intervertebral foramen, the dorsal root merges with the corresponding ventral root to form a mixed spinal nerve.
Sensory Function
The function of the dorsal roots is to carry sensory information from the body to the central nervous system. These signals, known as afferent signals, include a wide range of sensations like pain, temperature changes, fine touch, and vibration. They also convey proprioception, the body’s ability to sense its own position and movement.
Sensory information from the periphery, such as the skin or muscles, activates the neurons whose cell bodies are in the DRG. The nerve impulses travel through the dorsal root and into the spinal cord for processing. In contrast, the ventral roots carry motor signals from the central nervous system to muscles and glands.
Associated Medical Conditions
When dorsal roots or their ganglia are compromised, medical conditions can arise. Radiculopathy, or a “pinched nerve,” occurs when a dorsal root is compressed or inflamed. This is often caused by a herniated disc or spinal stenosis, a narrowing of the spinal canal. The compression leads to sharp pain, numbness, or tingling along the path of the affected nerve.
Another condition involving these structures is shingles (herpes zoster). The varicella-zoster virus, which causes chickenpox, can lie dormant for years within the dorsal root ganglion. If the virus reactivates, it travels down the sensory nerve fibers to the skin. This results in a painful, blistering rash that appears in a stripe-like pattern called a dermatome, the area of skin supplied by a single spinal nerve.