Dorsal root ganglion

The dorsal root ganglia are an enlargement of the dorsal root of spinal nerves representing the cell bodies of the primary somatosensory neurons.

Gross anatomy

Each dorsal root ganglion is oval and proportional in size to its related root. They are usually found just distal to the intervertebral foramina, immediately lateral to the perforation of the dura mater by the roots. The first cervical ganglion differs from the others in that it lies on the vertebral arch of the atlas while the second cervical ganglion is found behind the lateral atlantoaxial joint. Similarly, the sacral dorsal root ganglia are found within the vertebral canal.

Histology

The dorsal root ganglia contain the cell bodies of pseudounipolar neurons. A single neuron exits the cell body and bifurcates. One axonal branch extends to the periphery to provide sensory innervation to tissue while the other, shorter branch travels centrally to synapse with the central nervous system neuron. 

The dorsal root ganglion also serves as the target of inhibitory pain pathways from the central nervous system which act to blunt the nociceptive activity at the level of the primary somatosensory neuron.