Innervates skin of the face, mucous membranes in oral and nasal cavities, external ear, and teeth (general sensory).
Innervates muscles of mastication and other muscles in the neck, palate, and middle ear (skeletal motor).
Skull opening
Ophthalmic branch (V1) = Superior orbital fissure
Maxillary branch (V2) = Foramen rotundum
Mandibular branch (V3) = Foramen ovale.
Attachments to CNS
Sensory and motor roots attach to pons.
Nucleus of origin/destination in CNS
General sensory neurons project to the trigeminal sensory nuclei in the pons, medulla, and upper cervical spinal cord.
Motor fibers in CN V originate in the trigeminal motor (masticator) nucleus in the pons.
Details
Cranial nerve V is the largest cranial nerve. It is the major sensory nerve of theface. CN V emerges from the pons as two independent roots = a large sensory root and a smaller motor root.
All three branches of CN V carry general sensory fibers and their cell bodies are in the trigeminal ganglion, located in the floor of the middle cranial fossa. Central processes of sensory neurons make up the sensory root of V and these enter the pons (similar to a dorsal root of a spinal nerve entering the spinal cord) to relay on trigeminal sensory nuclei in the brainstem. CN V is sensory to the face, teeth, anterior tongue, oral cavity, and nasal cavity.
The motor (masticator) nucleus of V is located in the pons. Axons of these neurons leave the pons separate from the sensory root. CN V is motor to the muscles of mastication (chewing muscles) = masseter, temporalis, and the medial and lateral pterygoid muscles, the anterior belly of digastric and mylohyoid muscles in the neck, the tensor veli palatini muscle of the soft palate, and the tensor tympani muscle in the middle ear.
Figure 29.12 Dermatomes of V1, V2, and V3. ESSENTIAL NEUROSCIENCE, 2ND ED., FIGURE 14.8.
The two roots of CN V pass together into the middle cranial fossa just above the petrous portion of the temporal bone. Here the sensory root expands to form the trigeminal ganglion (containing cell bodies of afferent neurons). The ganglion is enclosed within an outpocketing of dura called the trigeminal cave (a.k.a. Meckel’s cave). The name “trigeminal” literally means “three twins”—which is a clever way of saying that each of the two nerves (right and left) has three branches.
Figure 29.13 Topography of trigeminal nerve branches. GRAY’S ANATOMY FOR STUDENTS, FIGURE 8.61.
Distal to the ganglion the trigeminal nerve divides into three branches: the ophthalmic, maxillary, and mandibular nerves. The branches are signified as V1, V2, and V3, respectively. The motor root of V continues inferior to the ganglion and joins the mandibular nerve = therefore only the mandibular branch contains motor fibers. The regions of facial skin (dermatomes) supplied by the three divisions of CN V, and the major branches from each of the divisions are shown in Figures 29.12 and 29.13.
V1 (Ophthalmic nerve) is a sensory nerve that supplies the eyeball, conjunctiva, nasal cavity, frontal air sinus, and skin of the nose, upper eyelid, forehead, and anterior scalp. It passes in the lateral wall of the cavernous sinus and enters the orbit through the superior orbital fissure. Near the superior orbital fissure V1 divides into the frontal, nasociliary, and lacrimal nerves.
V2 (Maxillary nerve) is a sensory nerve that supplies upper teeth and gums, palate, maxillary air sinus, and skin of the upper cheek, side of the nose, lower eyelid, upper lip, and the “temple” area on the side of the head. V2 is attached to the lateral wall of the cavernous sinus, and then passes through foramen rotundum to enter the pterygopalatine fossa. Within the pterygopalatine fossa many branches of V2 are given off, most notably the zygomatic, infra-orbital, greater and lesser palatine, and nasopalatine nerves.
Parasympathetic fibers associated with V2
Within the pterygopalatine fossa V2 is connected to the pterygopalatine ganglion = a parasympathetic ganglion. Preganglionic parasympathetic fibers derived from the facial nerve (VII) synapse here. Postganglionic parasympathetic fibers “hitch-a-ride” on branches of V2 into the orbit where they innervate the lacrimal gland. These visceral motor fibers cause the lacrimal gland to secrete tears.
V3 (Mandibular nerve) arises from the trigeminal ganglion and passes through foramen ovale to the infratemporal fossa. V3 is a mixed nerve. Within the infratemporal fossa V3 divides into large nerves such as the buccal, auriculotemporal, lingual and inferior alveolar nerves. The sensory portion of V3 supplies the lower teeth and gums, mucous membranes in the oral cavity and on the anterior tongue, and skin of the cheeks, lower lips, chin, external ear and middle scalp. The motor portion of V3 supplies the muscles of mastication and other muscles listed earlier.
Parasympathetic fibers associated with V3
Just inferior to foramen ovale in the infratemporal fossa, V3 is connected to the otic ganglion = a parasympathetic ganglion. Preganglionic parasympathetic fibers derived from the glossopharyngeal nerve (IX) synapse here. Postganglionic fibers hitch a ride on the auriculotemporal nerve ofV3 to the parotid gland. These fibers stimulate the parotid gland to secrete saliva.
Below the tongue, the lingual nerve of V3 is joined to the submandibular ganglion = a parasympathetic ganglion. Preganglionic parasympathetic fibers in the chorda tympani nerve (from CN VII) hitch-a-ride on the lingual nerve to the submandibular ganglion. Postganglionic parasympathetic fibers innervate the submandibular and sublingual salivary glands.
Important note
Cranial nerve V does not convey any PREganglionic parasympathetic fibers from the brainstem [Remember: only CNs III, VII, IX, and X are the cranial part of the craniosacral outflow!].
Postganglionic parasympathetic fibers simply “hitch rides” on distal branches of CN V to their destinations (e.g., lacrimal gland and salivary glands). The four parasympathetic ganglia in the head and their associations with the trigeminal nerve are shown in Figure 29.14.
Figure 29.14 Parasympathetic ganglia in the head and their connections to branches of CN V. GRANT’S ATLAS OF ANATOMY, 14TH ED., FIGURE 9.21.
A template for drawing the parts and pathway of the trigeminal nerve is also provided in the Cranial Nerves Appendix.
Cranial nerve VII: Facial nerve
Functions
Innervates muscles of facial expression and other muscles in the neck and middle ear (skeletal motor).
Supplies a small patch of skin in the external ear (general sensory).
Innervates the lacrimal gland and the submandibular and sublingual salivary glands (parasympathetic).
Carries taste from the anterior 2/3 tongue and palate (special sensory).
Skull opening
Enters the facial canal (within the temporal bone) via the internal acoustic meatus; Leaves the facial canal distally via the stylomastoid foramen.
Attachments to CNS
Junction of pons and medulla.
Nucleus of origin/destination in CNS
Skeletal motor fibers originate from facial motor nucleus in pons.
General sensory neurons project to trigeminal sensory nuclei.
Pre-ganglionic parasympathetic fibers originate from the superior salivatory nucleus in pons.
Taste fibers project to the nucleus solitarius in the medulla.
Details
Cranial nerve VII is a mixed nerve with a complicated course within the temporal bone. CN VII leaves the pons/ medulla junction just lateral to CN VI as two pieces: a larger part called the motor root of VII and a smaller portion called the nervus intermedius (so called because of its intermediate position between the motor root of VII and CN VIII).
The motor nucleus of the facial nerve is in the pons. Axons of these neurons make up the motor root of VII. The motor root of VII supplies the muscles of facial expression (mimetic muscles), aswell as the stapedius muscle in the middle ear and two muscles in the upper neck: the stylohyoid muscle and posterior belly of the digastric muscle.
General sensory information from a small area of skin in the external ear is carried by nerve fibers in the nervus intermedius of CN VII. Cell bodies of these afferent neurons are in the geniculate ganglion (sensory ganglion) of VII. Sources are not very clear on how these nerve fibers reach the external ear.
Cell bodies of preganglionic neurons are in the superior salivatory nucleus in the pons. Preganglionic axons are in the nervus intermedius. These fibers pass into two important branches of the facial nerve, the greater petrosal and chorda tympani nerves, and synapse on postganglionic neurons in the pterygopalatine and submandibular ganglia, respectively. Parasympathetic fibers in VII innervate the lacrimal gland (tear secretion), nasal glands (mucous secretion), and the submandibular and sublingual salivary glands.
Taste from the anterior two-thirds of the tongue is carried first in the lingual nerve (V3) then in the chorda tympani nerve of VII. Cell bodies of these afferent neurons are in the geniculate ganglion of VII. Central processes of the neurons pass into the brainstem via the nervus intermedius to synapse on the nucleus solitarius in the medulla. Also, there may be a few taste buds in the soft palate. These taste fibers are carried to the CNS via the greater petrosal nerve, with cell bodies in the geniculate ganglion as well.
Figure 29.15 Topography of facial nerve. FUNDAMENTALS OF ANATOMY AND PHYSIOLOGY, 10TH ED., FIGURE 14-24.
Together with cranial nerve VIII, the two parts of the facial nerve pass briefly through the posterior cranial fossa then enter the internal acoustic meatus. At the distal end of the meatus the two parts of VII fuse and the facial nerve enters the facial canal in the temporal bone.
Within the facial canal CN VII widens to form the geniculate ganglion. This contains cell bodies of afferent neurons in VII that carry taste and skin sensations. The part of the facial nerve that is bent from anterior to posterior here in the facial canal is called the genu of the facial nerve. From here, the facial nerve sweeps down behind the middle ear and emerges from the skull at the stylomastoid foramen. Just below the stylomastoid foramen the facial nerve gives off motor branches to the stylohyoid and posterior belly of the digastricmuscles.
CN VII then enters the parotid gland (but does not innervate it) and divides into terminal branches: temporal, zygomatic, buccal, mandibular, and cervical branches. These motor nerves spread across the face to supply the facial muscles (they make you smile, grin, grimace, pout, pucker, etc.).
Branches of CN VII in the Facial Canal
Figure 29.16 Branches of CN VII in the facial canal. GRAY’S ANATOMY FOR STUDENTS, FIGURE 8.129.Greater petrosal nerve: The greater petrosal nerve leaves CN VII at the genu. It passes through the petrous temporal bone and enters the floor of the middle cranial fossa. Here it dives down through the foramen lacerum to the pterygopalatine fossa. The greater petrosal nerve carries preganglionic parasympathetic fibers of VII to the pterygopalatine ganglion. These fibers supply the lacrimal gland and mucous glands in the nasal cavities.
Nerve to stapedius: The nerve to the stapedius leaves the facial canal, passes through the temporal bone, and supplies the stapedius muscle in the middle ear.
Figure 29.17 Diagram of facial nerve branches. GILROY, ATLAS OF ANATOMY.Chorda tympani nerve: The chorda tympani nerve leaves the facial nerve at the distal end of the facial canal, enters the tympanic cavity and crosses the medial surface of the eardrum (tympanicmembrane), then passes into the infratemporal fossa. Here it joins the lingual nerve of V3. The chorda tympani carries:
Taste fibers from the anterior two-thirds of the tongue. Cell bodies of these neurons are in the geniculate ganglion.
Preganglionic parasympathetic fibers—these “hitch-a-ride” on the lingualnerve of V3 to the submandibular ganglion where they synapse. Postganglionic fibers supply the submandibular and sublingual salivary glands.
This reflex protects the eyes via involuntary blinking of the eyelids in response to touching of the cornea.
Afferent portion = V1 (Trigeminal nerve). The ophthalmic divisionof CN V is sensory to the cornea.
Efferent portion = Facial nerve (temporal and zygomatic branches) that innervate the orbicularis oculi muscle—the muscle that brings the eyelids together and closes the palpebral fissure.
Clinical correlation
Herpes zoster (shingles) of the facial nerve (Ramsay Hunt Syndrome) manifests as blisters that appear in the external ear (dermatome of CN VII). Recall that the herpes zoster virus lives in the sensory ganglia of nerves (in this case, the geniculate ganglion of CN VII) and that shingles lesions appear along the course of sensory nerves in a dermatomal pattern.
Figure 29.16 Branches of CN VII in the facial canal. GRAY’S ANATOMY FOR STUDENTS, FIGURE 8.129.
There are three branches of the facial nerve given off within the facial canal:
The greater petrosal nerve leaves CN VII at the genu. It passes through the petrous temporal bone and enters the floor of the middle cranial fossa. Here it dives down through the foramen lacerum to the pterygopalatine fossa. The greater petrosal nerve carries preganglionic parasympathetic fibers of VII to the pterygopalatine ganglion. These fibers supply the lacrimal gland and mucous glands in the nasal cavities.
Figure 29.17 Diagram of facial nerve branches. GILROY, ATLAS OF ANATOMY.
The nerve to the stapedius leaves the facial canal, passes through the temporal bone, and supplies the stapedius muscle in the middle ear.
The chorda tympani nerve leaves the facial nerve at the distal end of the facial canal, enters the tympanic cavity and crosses the medial surface of the eardrum (tympanicmembrane), then passes into the infratemporal fossa. Here it joins the lingual nerve of V3. The chorda tympani carries:
Taste fibers from the anterior two-thirds of the tongue. Cell bodies of these neurons are in the geniculate ganglion.
Preganglionic parasympathetic fibers—these “hitch-a-ride” on the lingualnerve of V3 to the submandibular ganglion where they synapse. Postganglionic fibers supply the submandibular and sublingual salivary glands.
Carries blood pressure and blood gas information from carotid sinus and carotid body (visceral sensory).
Innervates parotid gland (parasympathetic).
Carries taste from posterior 1/3 tongue (special sensory).
Skull opening
Jugular foramen.
Attachments to CNS
Medulla.
Nucleus of origin/destination in CNS
General sensory fibers project to trigeminal sensory nuclei.
Skeletal motor fibers arise from nucleus ambiguus in the medulla.
Visceral sensory fibers from baro/chemoreceptors project to nucleus solitarius in the medulla.
Pre-ganglionic parasympathetic fibers arise from the inferior salivatory nucleus in the medulla.
Taste fibers project to the nucleus solitarius in the medulla.
Details
Cranial nerve IX receives its name since it carries afferent fibers from the tongue and pharynx. CN IX emerges from the medulla and leaves the cranial cavity through the jugular foramen. Within the jugular foramen two swellings appear on the nerve: the superior and inferior (sensory) ganglia of IX. These contains cell bodies of the sensory neurons within CN IX.
Motor fibers in CN IX supply one skeletal muscle = the stylopharyngeus—which elevates the pharynx during swallowing. Cell bodies are in the nucleus ambiguus in the medulla.
Two categories of sensory fibers are contained in IX. Cell bodies of these neurons are in the sensory ganglia of CN IX, located in the jugular foramen.
General sensory fibers supply the mucous membranes of the tympaniccavity, the posterior 1/3 of the tongue, the tonsillar fossa and palatine tonsils, the soft palate, and the upper pharynx. Sore throat pain and pain from tonsillitis is transmitted through CN IX. The afferent part of the “gag reflex” is carried to the CNS via IX.
Visceral sensory fibers supply the carotid sinus and carotid body—both located near the bifurcation of the common carotid artery. Sensory fibers from the sinus and the body are transmitted via the carotid branch of IX.
The carotid sinus is a dilated region of the proximal part of the internal carotid artery (just distal to the bifurcation). Receptors in the wall of the carotid sinus (baroreceptors) detect changes in blood pressure. The carotid body is a small vascular organ (like a tiny berry) located in the crotch of the bifurcating common carotid artery. Chemoreceptors in the carotid body detect changes in blood levels of O2, CO2, as well as pH levels.
Cell bodies of preganglionic neurons are in the inferiorsalivatorynucleus in the medulla. Preganglionic fibers are carried in the lesserpetrosalnerve, a branch of IX. These nerve fibers synapse on neurons in the otic ganglion in the infratemporalfossa. Postganglionic fibers “hitch-a-ride” on the auriculotemporal nerve (ofV3) to the parotid gland. CN IX innervates the parotid gland, causing it to secrete saliva.
Taste buds on the posterior one-third of the tongue are carried in lingual branches of IX. Cell bodies of these afferent neurons are in the sensory ganglia of IX. Central processes of neurons synapse on cells in the nucleus solitarius in the medulla.
After leaving the cranial cavity through the jugular foramen, CN IX descends deep to the styloid process between the internal and external carotid arteries and curves anteriorly around the stylopharyngeus muscle. From here it enters the pharynx by passing through the gap between the superior and middle constrictor muscles of the pharynx. It terminates near the base of the tongue.
Branches of CN IX
Tympanicnerve (Jacobsen’s nerve): Arises from CN IX just below the jugular foramen and passes superiorly into the tympaniccavity. The tympanic nerve carries sensory fibers from mucosa in the tympanic cavity and preganglionic parasympathetic motor fibers that will innervate the parotid. In the tympanic cavity, the tympanic nerve contributes fibers to the tympanic plexus. Some of the fibers of the tympanic nerve will reunite distal to the tympanic plexus to form the lesser petrosal nerve = these contain preganglionic parasympathetic fibers. The lesser petrosal nerve leaves the tympanic cavity, enters the middle cranial fossa, then drops down into the infratemporal fossa through foramen ovale. Here preganglionic fibers synapse on neurons in the otic ganglion. Post-ganglionic fibers reach the parotid gland via the auriculotemporal nerve (of V3).
Carotid branch: Contains visceral sensory fibers; supplies the carotid sinus and carotid body.
Pharyngeal branches: These become part of the pharyngeal plexus of nerves. Pharyngeal branches of IX are sensory to the mucous membranes of the oropharynx, nasopharynx, and pharyngotympanic (auditory) tube.
Tonsillar branch: Sensory to mucosa of the tonsillar fossa and palatine tonsils.
Lingual branches: Taste and general sensation to posterior 1/3 of tongue.
A template for drawing the pathway of the glossopharyngeal nerve is also provided in the Cranial Nerves Appendix.
Cranial nerve X: Vagus nerve
Functions
Innervates skeletal muscles of the palate, pharynx, and larynx (skeletal motor).
Innervates mucosa of lower pharynx and entire larynx (general sensory).
Innervates skin of the external acoustic meatus (general sensory).
Supplies mucosa of GI tract organs, from esophagus to distal transverse colon (visceral sensory).
Carries blood pressure and blood gas information (baroreception and chemoreception) from vessels in the thorax (visceral sensory).
Innervates cardiac muscle and smooth muscle and glands in the GI tract, from esophagus to distal transverse colon (parasympathetic).
Carries taste from epiglottis (special sensory).
Skull opening
Jugular foramen.
Attachments to CNS
Medulla.
Nucleus of origin/destination in CNS
Skeletal motor fibers arise from nucleus ambiguus in the medulla.
General sensory fibers project to the trigeminal sensory nuclei.
Visceral sensory fibers project to nucleus solitarius in the medulla.
Preganglionic parasympathetic fibers arise from the dorsal motor nucleus of vagus in the medulla.
Taste fibers project to the nucleus solitarius in the medulla.
Details
CN X has an extensive distribution as you probably already know—to the head, neck, thorax, and to the abdomen as far south as the distal transverse colon. Thus, the vagus is the “wanderer” (vagabond). It emerges from the medulla as a series of rootlets that unite in the posterior cranial fossa and pass out of the skull through the jugular foramen. Near the jugular foramen the vagus is enlarged to form sensory ganglia of CN X. These ganglia contain cell bodies of sensory neurons.
The cell bodies of these motor neurons are in nucleus ambiguus of the medulla. The efferent part of the “gag” reflex is carried via the vagus. Here’s a run-down of muscles supplied by CN X:
Soft palate: Levator veli palatini, palatoglossus.
Pharynx: Palatopharyngeus; superior, middle, and inferior constrictors.
Larynx: All intrinsic muscles of the larynx (the muscles of phonation).
General sensory fibers supply the meninges in the posterior cranial fossa, the external surface of the tympanic membrane, and skin of the external acoustic meatus. Cell bodies of these sensory neurons are in the sensory ganglia of X.
General sensory fibers supply mucous membranes located at the base of the tongue, on the epiglottis, the laryngopharynx, and the larynx. Cell bodies of these afferent neurons are in the sensory ganglia of X.
Visceral sensory fibers in the vagus nerve transmit non-pain visceral sensations = nausea, upset tummy, stretch, bloating, etc. from organs in the thorax and abdomen. The vagus carries visceral sensory information from baroreceptors and chemoreceptors situated in the aorta and pulmonary trunk. Also, information concerning distension (filling) of air tubes and alveoli in the lungs is carried in sensory neurons of CN X. Cell bodies of all these visceral sensory neurons are in the sensory ganglia of X.
Cell bodies of preganglionic neurons are in the dorsal motor nucleus of the vagus in the medulla. Visceral motor fibers stimulate cardiac muscle in the heart and smooth muscle in thoracic and abdominal organs—all the way to the distal part of the transverse colon. Secretomotor fibers supply glands in the pharynx, larynx, and thoracic and abdominal organs. Preganglionic fibers in CN X synapse on postganglionic neurons in intramural ganglia, within (or near) the walls of target organs, and on pacemaker cells in the heart.
A small number of taste buds exist on the base of the tongue and epiglottis. These are supplied by afferent neurons in CN X. Cell bodies are in the sensory ganglia of X.
Figure 29.19 Topography of the vagus nerve. CLINICALLY ORIENTED ANATOMY, FIGURE 9.16.
After passing through the jugular foramen, the vagus descends within the carotid sheath between the internal jugular vein and common carotid artery. At the base of the neck the vagi pass through the superior thoracic aperture to enter the mediastinum.
Branches of the CN X
Auricular branch (Arnold’s nerve): Arises just below the jugular foramen and passes through a fissure in the skull to reach the external ear where it supplies the external acoustic meatus and tympanic membrane. Cool fact: Cleaning your external meatus can produce a coughing fit—this a vagal reflex—the afferent part of this reflex is transmitted through the auricular branch of X.
Pharyngeal branches of X: Motor branches that join the pharyngeal branches of IX (sensory) to form the pharyngeal plexus. Pharyngeal branches of X innervate muscles of the soft palate and pharynx, including the constrictor muscles.
Superior laryngeal nerve: Divides into internal and external laryngeal nerves. The internal laryngeal nerve is sensory to the upper larynx and laryngopharynx (“Guardian of the airway”). The external laryngeal nerve innervates the cricothyroid muscle.
Cardiacbranches: Branch from the vagi in the neck and descend into the thorax where they supply the heart. What is their function?
Recurrent laryngeal nerves: Old friends of ours—we encountered them earlier in the thorax. Innervate all the intrinsic muscles of the larynx (except one) and supply the mucosa of the inferior larynx.
