All the sympathetic ganglia that send postganglionic nerve fibres to structures in the head, neck and upper limb receive preganglionic fibres from the central nervous system only through the white rami communicates of the upper thoracic ventral rami. These preganglionic fibres ascend in the trunk and reach its ganglia directly and outlying ganglia through branches of the trunk. Thus destruction of the trunk at the root of the neck, whether as a result of a surgery (cervical sympathectomy) or of some pathological condition,isolates all these sympathetic ganglion cells from the central nervous system and prevents them from responding to reflex or emotional changes in the central nervous system.
Cunningham's Manual of Practical Anatomy: Volume III: Head, Neck and Brain (Oxford Medical Publications)
G. J. Romanes
Paperback - Nov 20, 1986