Dorsal root ganglion

Structure

The term ganglion refers to a cluster of the neuronal cell bodies in the peripheral nervous system. The spinal ganglion contains the cell bodies of sensory neurons situated in the posterior root of each spinal nerve (except for spinal nerve C1). These neurons are known as first-order neurons of the somatosensory system and carry sensations related to touch, vibration, proprioception, pain and temperature. Their cell bodies are typically variable in size but all are encapsulated by satellite glial cells which prevent the impulse transmission between them.

All cell bodies contained in the spinal ganglion are considered to belong to pseudounipolar neurons, which are a variation of bipolar neurons. These neurons have specialized structures: cell bodies that extend a short axon that quickly terminates by bifurcating into two processes, central and peripheral. The peripheral process carries information from the periphery through the spinal nerve (together with motor fibers), while the shorter central process extends towards the posterior horns of the gray matter of the spinal cord.

Because of this specific ‘T-shaped’ structure of pseudounipolar neurons, impulses generated in the periphery bypass the cell bodies in the spinal l root ganglion and continue directly to the spinal cord through the central process of the neuron.

Spinal ganglia are ensheathed by extensions of the spinal meninges, which are replaced by a connective tissue covering known as epineurium at the level of the spinal nerve.

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Function

The spinal ganglion contains the cell bodies of all sensory nerve fibers in the spinal nerve, , thus it has a crucial role in sensory transmission in the human body. More specifically, its main function is to relay the sensory nerve impulses from the periphery to the peripheral nervous system. The cell bodies contain genetic information and organelles which direct and drive cellular activity, as well as maintain the structure of the neuron.

The sensory impulses generated in the periphery (pain, touch, temperature changes) activate the peripheral processes of the spinal ganglion neurons. These impulses then travel to the spinal cord either directly (bypassing the cell bodies) or through the neuronal cell body in the dorsal root ganglion. It has been long believed that these cell bodies acted as storage "helpers" in transmitting impulses, such as pain impulses (nociception). However, it has been shown that these neural bodies are indeed active participants in the regulation of this signaling process.