The phrenic nerves contain motor, sensory, and sympathetic nerve fibers.

Ganglioneuroma is a tumor of the sympathetic nerve fibers arising from neural crest cells.

The short ciliary nerve contains parasympathetic and sympathetic nerve fibers.

It carries postsynaptic sympathetic nerve fibers to the pterygopalatine ganglion, also known as the sphenopalatine ganglion.

It receives innervation from postganglionic sympathetic nerve fibers arriving via the ilioinguinal nerve and the posterior scrotal nerve.

The SCN stimulates the release of Norepinephrine from sympathetic nerve fibers from the superior cervical ganglia that synapse with the pinealocytes.

The sympathetic nerve fibers act to constrict the blood vessels in some places (as in the skin and viscera) and to dilate them in others (as in the heart and skeletal muscles).

Thus, the sympathetic nerve fibers act to accelerate the heartbeat, dilate the pupil of the eye and the bronchi of the lungs, and inhibit the activity of the smooth muscles of the alimentary canal.

An increase in sympathetic nervous system stimulation causes the heart rate to increase, both by the direct action of sympathetic nerve fibers on the heart and by causing the endocrine system to release hormones such as epinephrine (adrenaline), which have a similar effect.

The ganglia include not just the sympathetic trunks but also the cervical ganglia (superior, middle and inferior), which sends sympathetic nerve fibers to the head and thorax organs, and the celiac and mesenteric ganglia (which send sympathetic fibers to the gut).

There may also be abnormalities of the part of the nervous system that controls involuntary functions (autonomic nervous system) such as damage to or abnormalities of certain nerve fibers (sympathetic nerve fibers) that pass from the spinal cord to the neck and/or pelvic area.