THE PARAGANGLION SYSTEM

The paraganglion system denotes a collection of chromaffin cells distributed in extra-adrenal sites. These cells arise from the primitive neural crest, and are thought to provide a vital source of catecholamines during fetal development prior to the formation of the adrenal medulla. Most of the paraganglionic cells degenerate after birth. Of those that remain, some develop into a group of specialized chemoreceptors distributed throughout the body.

In the head and neck, paraganglia can be found symmetrically distributed in close proximity to arteries and nerves. For example, the carotid bodies are specialized paraganglia located in the adventitia of the carotid bifucations which serve as chemoreceptors to regulate respiration and maintain arterial gases.

The paraganglia of the temporal bone can be found accompanying Jacobson's nerve (the tympanic branch of CN IX), Arnold's nerve (the auricular branch of CN X), within the mucosa of the cochlear promontory, as well as within the inferior tympanic canaliculus. Somewhat more than half of the paraganglia of the temporal bone are located in the jugular fossa.

The intravagal paraganglia are comprised of small cell groups dispersed in the perineurium of the vagus nerve.