A stellate ganglion block is a treatment approach for upper body pain that is caused by damaged ganglion nerves. The sympathetic chain consists of ganglion nerve bundles that run along the spinal cord and extend down the trunk of the body. The nerves extend to various parts of the body and control numerous unconscious functions such as heart rate as well as conscious biological processes. Ganglia are clusters of nerve endings called nexuses and essential ganglia are located throughout the sympathetic nervous system. A single network of these nerve endings has the ability to control sensations and movement.