Nerve Supply of Mouth
and Pharynx
Six of the 12 pairs of cranial nerves contribute to the nerve supply of the
mouth and pharynx. The trigeminal nerve (cranial nerve V) emerges from
the lateral surface of the pons as a larger sensory and a smaller motor root. A
short distance from the pons the sensory root is expanded by the presence of
many afferent nerve cell bodies into the trigeminal ganglion, which lies
in a depression on the apex of the petrous portion of the temporal bone. From
the anterior margin of this ganglion arise the ophthalmic, maxillary, and
mandibular divisions of the trigeminal nerve. The motor root courses along the
medial and then the inferior side of the sensory root and ganglion and joins
the mandibular nerve near its beginning. The maxillary division
passes through the foramen rotundum into the pterygopalatine fossa, where it
gives off the following branches: (1) two or three branches to the sphenopalatine
ganglion, which leave the ganglion as a pharyngeal branch passing through a
bony canal to the mucous membrane of the upper part of the nasopharynx, the palatine
nerves passing through the pterygopalatine canal to exit through the
greater and lesser palatine foramina to supply the mucous membrane of the
palate, and a sphenopalatine branch, which enters the nasal cavity and runs along the nasal septum to
reach the palate through the incisive foramen; (2) the posterior superior
alveolar nerves, which enter the maxilla and supply the molar teeth and
related gums. The maxillary nerve continues as the infraorbital nerve, which
gives off the middle and anterior superior alveolar nerves in the
infraorbital canal and a branch to the upper lip after it reaches the face. The
mandibular nerve reaches the infratemporal fossa through the foramen ovale and
has the following branches: (1) nerves to each of the muscles of mastication
(the nerve to the medial pterygoid also supplying the tensor veli
palatini muscle); (2) the inferior alveolar, which, before entering the
mandibular foramen, gives off the mylohyoid branch to that muscle and
the anterior belly of the digastric, courses through the alveolar canal
supplying the mandibular teeth, and ends as the mental nerve, which
exits through the mental foramen to give sensory supply to the chin and part of
the lower lip; (3) the buccal nerve giving sensory supply to the cheek;
and (4) the lingual nerve, which, after receiving the chorda tympani
from the facial nerve, courses inferiorly and then anteriorly on the lateral
surface of the hyoglossus muscle to reach the undersurface of the tongue. The
trigeminal fibers in the lingual nerve carry general sensation from the
anterior two thirds of the tongue.
The facial nerve (cranial nerve
VII) emerges from the lateral side of the pontomedullary junction as a larger
motor and a smaller sensory root (nervus intermedius), containing general
visceral efferent fibers of VII as well as afferent fibers. It leaves the
cranial cavity by way of the internal acoustic meatus and then goes through the
facial canal to exit the stylomastoid foramen, where it gives off
branches to the stylohyoid muscle and posterior belly of the digastric. The
facial nerve runs anteriorly through the substance of the parotid gland,
crosses the external carotid artery, and divides in the substance of the gland
into branches that leave the anterior border of the parotid gland to innervate
the muscles of facial expression, of which the ones surrounding the oral
orifice, including the buccinator, are of interest in this discussion. The geniculate
ganglion is present within the facial canal at a sharp bend in the nerve.
Proximal to the ganglion, the nerve gives off the greater petrosal nerve, which
eventually reaches the pterygopalatine ganglion. Distal to the ganglion it
gives off the chorda tympani, which eventually joins the lingual nerve,
carrying special visceral afferent fibers, which carry taste sensation from the
anterior two thirds of the tongue, as well as preganglionic parasym athetic
axons, which go to the submandibular ganglion.
The glossopharyngeal nerve (cranial
nerve IX) emerges by a series of rootlets from the cranial part of the groove
between the inferior cerebellar peduncle and the inferior olive of the medulla.
It leaves the cranial cavity through the jugular foramen near which it exhibits
two ganglionic swellings, courses downward along the posterior border of the
stylopharyngeus muscle, and disappears deep to the hyoglossus muscle to ramify
into its terminal branches to the tongue. The tympanic branch of the
glossopharyngeal nerve follows a bony canal from the margin of the jugular
foramen to the tympanic cavity, where it helps to form the tympanic plexus and
then continues as the lesser petrosal nerve, which eventually brings
preganglionic parasympathetic axons to the otic ganglion. The pharyngeal
branches of the glossopharyngeal nerve mostly join with the pharyngeal branches
of the vagus and branches of the superior cervical ganglion to form the
pharyngeal plexus, which supplies the muscles of the pharynx (except the stylopharyngeus, entirely glossopharyngeal) and the muscles of the soft palate
(except the tensor veli palatini, mandibular branch of trigeminal). The
pharyngeal plexus consists of motor axons from the vagus and sensory axons to
the mucous membrane via the glossopharyngeal, except for a muscular branch of
the glossopharyngeal that innervates the stylopharyngeus muscle. The tonsillar
branches arise near the base of the tongue and supply also the soft palate
and the fauces. The lingual and terminal branches of IX take care
of both the general sense and the sense of taste of the posterior one third of
the tongue and the pharyngoepiglottic folds.
The vagus nerve (cranial nerve
X) emerges just inferior to the glossopharyngeal nerve. It also leaves the
cranial cavity by way of the jugular foramen and has two ganglionic swellings
in this region, one at the foramen and one below the foramen. Entering the
carotid sheath, the vagus courses inferiorly in the neck between the internal
jugular vein and the internal or common carotid artery. Some branches of the
vagus contribute to the supply of the mouth and pharynx. The pharyngeal
branches (variable in number) supply motor axons to the pharyngeal plexus.
The superior laryngeal nerve divides into external and internal
branches. The external branch runs inferiorly and anteriorly on the external
surface of the inferior pharyngeal constrictor to innervate the cricothyroid
and cricopharyngeus muscles and a variable amount of the inferior pharyngeal
constrictor. The internal branch pierces the thyrohyoid membrane and divides
into an ascending and a descending branch, the former going to the mucous
membrane covering the epiglottis and a small adjacent part of the tongue and
the latter supplying the mucous membrane on the pharyngeal surface of the
larynx in addition to its laryngeal distribution. The recurrent laryngeal
branch of the vagus gives some supply to the inferior pharyngeal constrictor
muscle as the branch passes under the inferior border of this muscle in
entering the larynx.
The hypoglossal nerve (cranial
XII) emerges by a series of rootlets from the sulcus between the inferior olive
and the medullary pyramid. It leaves the cranial cavity by way of the
hypoglossal canal and runs inferiorly and anteriorly, passing lateral to the
carotid bifurcation and between the internal carotid artery and the internal
jugular vein. It becomes superficial to the vessels near the angle of the
mandible, where it passes across the external carotid and lingual arteries deep
to the digastric muscles. From here it continues anteriorly between the
mylohyoid and hyoglossus muscles. The hypoglossal nerve supplies the intrinsic
muscles of the tongue, as well as the styloglossus, hyoglossus, and
genioglossus muscles. Fibers from the first and second cervical nerves run with
the hypoglossal to supply the geniohyoid and thyrohyoid muscles.
The areas of sensory supply of the
mucous membrane of the oral cavity and pharynx, shown diagrammatically in the
accompanying illustration, are only approximations because no complete
agreement as to their limits exists.
