Internal carotid plexus

The internal carotid plexus refers to a meshwork of neurons which is situated on the lateral side of internal carotid artery. This plexus receives post-ganglionic sympathetic neurons via a branch of the superior cervical ganglion, called the internal carotid nerve. Thereupon, the sympathetic fibers within the internal carotid plexus, follow the course of internal carotid artery and ascend through the carotid canal to enter the cranial cavity. These post-ganglionic sympathetic neurons get distributed to various intracranial structures.

For instance, in case of eyes, the post-ganglionic sympathetic neurons either commute through the nasociliary nerve and its long and short ciliary nerve branches or they follow the ophthalmic arterial branches of internal carotid artery, to reach the eye ball. Here, sympathetic neurons innervate two muscles, namely the dilator pupillae muscle of iris and the levator palpabrae superioris muscle. Contraction of the former brings about mydriasis, while the latter prevents drooping of the eye lid.

Some fibers come off from the internal carotid plexus as the deep petrosal nerve that transmits post-ganglionic sympathetic neurons to the pterygopalatine ganglion via the nerve of pterygoid canal. The latter also carries parasympathetic neurons from the facial nerve nucleus. From the ganglion onwards, the sympathetic innervation gets distributed to nasal cavities, palate and paranasal sinuses via branches of pterygopalatine ganglion and maxillary nerve. Those postganglionic sympathetic fibers that are meant to innervate the lacrimal gland, undertake a longer route as they hop off from the pterygopalatine ganglion onto the maxillary nerve via ganglionic communicating branches and jump one more time from maxillary to ophthalmic nerve to eventually innervate the lacrimal gland.

A few of the postganglionic sympathetic fibers follow the course of caroticotympanic branches of internal carotid artery to reach the tympanic plexus (in the middle ear) as caroticotympanic nerves. From this point, the post-ganglionic neurons eventually travel through the auriculotemporal nerve to reach the parotid gland.

Please not that unlike the parotid, the sympathetic neurons to the submandibular and sublingual salivary glands reaches onto them by following the branches of external carotid artery, such as, facial and lingual arteries.