ABSTRACT
The abducens nerve (AN; cranial nerve VI) exits the brainstem at the inferior pontine sulcus, pierces the dura of the posterior cranial fossa, passes through the cavernous sinus in close contact to the internal carotid artery (ICA) and traverses the superior orbital fissure to reach the orbit to innervate the lateral rectus muscle. At its exit from the brainstem, the AN includes only axons from lower motor neurons in the abducens nucleus. However, as the AN crosses the ICA it receives a number of branches from the internal carotid sympathetic plexus. The arrangement, neurochemical profile and function of these sympathetic axons running along the AN remain unresolved. Herein, we use gross dissection and microscopic study of hematoxylin and eosin-stained sections and sections with tyrosine hydroxylase immunolabeling. Our results suggest the AN receives multiple bundles of unmyelinated axons that use norepinephrine as a neurotransmitter consistent with postganglionic sympathetic axons.
ABSTRACT
The glossopharyngeal nerve (CN IX) provides innervation to the parotid gland, carotid body/sinus, mucosa of the middle ear, tongue and oropharynx and the stylopharyngeus muscle. The vagus nerve provides innervation to the remaining skeletal muscle of the pharynx. CN IX contributes to the pharyngeal plexus and normally provides innervation to the mucosa of the oropharynx. Herein, we describe a previously undescribed variation of CN IX. CN IX was observed to enter the pharyngeal wall but instead of forming terminal branches in the tonsillar fossa, CN IX descended along the posterior wall between the mucosa and pharyngeal constrictors to the esophagus. This unusual branch of CN IX gave rise to numerous branches along the pharynx but did not intermingle with laryngeal branches from the vagus nerve. From this dissection, we developed innervation maps of the pharynx and propose a central miswiring mechanism for this unusual variation.
ABSTRACT
The glossopharyngeal nerve (CN IX) provides innervation to the parotid gland, carotid body/sinus, mucosa of the middle ear, tongue and oropharynx and the stylopharyngeus muscle. The vagus nerve provides innervation to the remaining skeletal muscle of the pharynx. CN IX contributes to the pharyngeal plexus and normally provides innervation to the mucosa of the oropharynx. Herein, we describe a previously undescribed variation of CN IX. CN IX was observed to enter the pharyngeal wall but instead of forming terminal branches in the tonsillar fossa, CN IX descended along the posterior wall between the mucosa and pharyngeal constrictors to the esophagus. This unusual branch of CN IX gave rise to numerous branches along the pharynx but did not intermingle with laryngeal branches from the vagus nerve. From this dissection, we developed innervation maps of the pharynx and propose a central miswiring mechanism for this unusual variation.
