What is ganglion. Write its function.

The group of small nerves present inside the vertebral column which are located near the spinal cord is called ganglion. It communicates between spinal cord and brain. 

A dorsal root ganglion (or spinal ganglion; also known as a posterior root ganglion) is a cluster of neurons (a ganglion) in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the dorsal root ganglia.

Ganglia are ovoid structures containing cell bodies of neurons and glial cells supported by connective tissue. Ganglia function like relay stations - one nerve enters and an other exits.