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Chapter Outline

Key Terms

18Cranial Nerves

Cranial Nerves

Cranial Nerve Modalities

I. Olfactory Nerve

Clinical ConsiderationsII. Optic Nerve

Clinical ConsiderationsIII. Oculomotor Nerve

Clinical ConsiderationsIV. Trochlear Nerve

Clinical Considerations

V. Trigeminal Nerve

V1 Ophthalmic NerveV2 Maxillary NerveV3 Mandibular NerveClinical Considerations

VI. Abducens Nerve

Clinical ConsiderationsVII. Facial Nerve

Clinical ConsiderationsVIII. Vestibulocochlear Nerve


IX. Glossopharyngeal Nerve

Clinical ConsiderationsX. Vagus Nerve

Clinical ConsiderationsXI. Accessory Nerve

Clinical ConsiderationsXII. Hypoglossal Nerve


Cranial Nerve Modalities represent theseven specific functional componentstransmitted within the cranial nerves,including afferent (sensory) as well asefferent (motor) modalites. Althougheach cranial nerve may transmit one toseveral modalities, none carry all ofthem; thus, each cranial nerve pos-sesses specific modalities that areresponsible for receiving sensory inputfrom receptors or delivering outputfrom its motor component. Anadditional component, general proprio-

ception (GP), is generally understood, ifnot specified, as sensory input fromwithin the muscles innervated by thosecranial nerves.

Motor Modalities:

General somatic efferent (GSE)represents motor innervation toskeletal muscles developed fromsomites.

General visceral efferent (GVE) repre-sents motor fibers that innervate

smooth muscles, cardiac muscles,and glands.

Special visceral efferent (SVE) repre-sents motor fibers to skeletal musclesof branchiomeric origin ( pharyngealarch origin).

Sensory Modalities:

General somatic afferent (GSA)represents general sensation (touch, pres-sure, temperature, pain) from the skinabout the anterior face and lateral head.

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Chapter 18 Cranial Nerves 279

CRANIAL NERVE MODALITIES

General somatic afferent (GSA)—General sensationin function. For example, the trigeminal nerveserves much of the skin and the mucous mem-branes of the face, whereas the facial, glossopha-ryngeal, and vagus nerves serve the area of the earwith general sensation.

General somatic efferent (GSE)—General motor infunction to skeletal muscles. This grouping is car-ried by the oculomotor, trochlear, abducent, andhypoglossal nerves innervating musculature de-rived from somites.

General visceral afferent (GVA)—General sensationfrom the viscera included in the facial, glossopha-ryngeal, and vagus nerves.

General visceral efferent (GVE)—Visceral motor(parasympathetic) to the viscera. Only four cra-nial nerves transmit parasympathetic fibers: theoculomotor, facial, glossopharyngeal, and vagusnerves.

Special somatic afferent (SSA)—Special sensory infunction from the eye and ear. The cranial nervescarrying this component are the optic and vestibu-locochlear nerves.

Special visceral afferent (SVA)—Special sensory infunction from the viscera. These fibers are associ-ated with the special senses of smell, carried in theolfactory nerve; and taste, transmitted in the fa-cial, glossopharyngeal, and vagus nerves. An easyway to remember the difference between SSA andSVA fibers is that for SVA fibers to be activated, thematerial has to be dissolved in a fluid (saliva ormucus).

Special visceral efferent (SVE)—Special motor to thebranchiomeric musculatures. This component iscarried to the muscles derived from the pharyn-geal arches and is transmitted by the nerves ofthose arches: the trigeminal, facial, glossopharyn-geal, accessory (contributions to the pharyngealplexus), and vagus nerves.

As with the typical spinal nerve, cell bodies of af-ferent nerve fibers of cranial nerves are located insensory ganglia outside the central nervous system,that is, outside the brain. Central processes of these

CRANIAL NERVES

Twelve pairs of cranial nerves originate in the brain,leave its surface, and pass through certain foraminaof the skull to be distributed in and about the headand neck. One cranial nerve, the vagus, continuesinto the thorax and abdomen to innervate some of theviscera. The cranial nerves are named and numberedsequentially with roman numerals, progressing ros-trally to caudally:

I. OlfactoryII. OpticIII. OculomotorIV. TrochlearV. TrigeminalVI. AbducensVII. FacialVIII. VestibulocochlearIX. GlossopharyngealX. VagusXI. AccessoryXII. Hypoglossal

Three figures appearing earlier in the book canbe reviewed to observe the relative positions of thecranial nerves emerging from the brain (Figs. 17-3and 17-4) and their relative positions in the floor ofthe cranial vault (Fig. 9-2).

As explained earlier, peripheral nerves consist ofseveral nerve fiber types specific for their function.Typically, each peripheral nerve contains somaticand visceral components, each with afferent and ef-ferent fibers.

Peripheral nerves emanating from the brain(known as cranial nerves) are more complex thanthose arising from the spinal cord, since these nervesserve special sensory functions—such as hearing, see-ing, smelling, and tasting—in addition to supplyingspecial skeletal muscles of branchiomeric origin.

The cranial nerves, then, carry certain compo-nents in addition to the general somatic and generalvisceral components carried by spinal nerves, desig-nated as special somatic afferent, special visceral af-ferent, and special visceral efferent.

General visceral afferent (GVA) representsgeneral sensation from the viscera, gener-ally perceived as pressure and/or pain.

Special somatic afferent (SSA) representsspecial sensation from the eye (vision)and the ear (auditory and equilibrium).

Special visceral afferent (SVA)represents visceral sensations of smell(olfaction) and taste (gustatory).

280 Chapter 18 Cranial Nerves

fibers pass via the cranial nerves into the brain to ter-minate on neurons that relay impulses for process-ing, sorting out, and coordinating the information be-fore initiation of a motor response that may or maynot be at a conscious level.

All of the interconnections and workings of thebrain are extremely complicated and beyond thescope of this text. Readers who want more informa-

tion about this subject are referred to standard text-books of neuroanatomy.

Each of the 12 cranial nerves is described in thefollowing sections, including information on the loca-tion of the cell bodies, the components carried, con-nections with other nerves, and finally the distribu-tion and function. A summary of this information ispresented in tabular form in Table 18-1.

Nerve Components Cell Bodies Peripheral Distribution Function

I Olfactory SVA Olfactory epithelial cells Olfactory nerves Smell

II Optic SSA Ganglion cells of retina Rods and cones Vision

III Oculomotor GSE Nucleus III Levator palpebrae; recti: superior, Eyemedial, inferior; and inferior oblique movement

GVE Edinger-Westphal Ciliary ganglion—Ciliary body— Contraction ofnucleus Sphincter pupillae pupil and

accomodationGP Mesencephalic Ocular muscles Kinesthetic

nucleus V sense

IV Trochlear GSE Nucleus IV Superior oblique Ocularmovement

GP Mesencephalic Superior oblique Kinestheticnucleus V sense

V Trigeminal GSA Trigeminal ganglion Ophthalmic, maxillary, and Generalmandibular divisions to mucous sensationmembranes and skin of faceand head

SVE Motor nucleus V Temporalis, masseter, pterygoids, Masticationanterior belly of digastric, mylohyoid,tensors palatini and tympani

GP Mesencephalic Muscles of mastication Kinestheticnucleus V sense

VI Abducens GSE Nucleus VI Lateral rectus Eyemovement

GP Mesencephalic Lateral rectus Kinestheticnucleus V sense

VII Facial SVE Motor nucleus VII Muscles of facial expression, Facialstapedius, stylohyoid, post, belly of expressiondigastric

GVE Salivatory nucleus Greater petrosal— pterygopalatine Secretomotorganglion—nasal mucosa, lacrimalgland; chorda tympani—lingual nerve, submandibular ganglion—submandibular, sublingual glands

SVA Geniculate ganglion Chorda tympani—lingual nerve- Tastetaste buds anterior two-thirds tongue

GVA Geniculate ganglion Greater petrosal, chorda tympani Visceralsensation

GSA Geniculate ganglion Auricular branch—ear and mastoid Cutaneoussensation

Table 18-1 Cranial Nerves

(continued)


Nerve Components Cell Bodies Peripheral Distribution Function

VIII Vestibulocochlear SSA Spiral ganglion Organ of Corti HearingSP Vestibular ganglion Vestibular mechanism Balance

IX Glosso-pharyngeal SVA Inferior ganglion IX Lingual br.—taste buds posterior one- Tastethird tongue, circumvallate papillae

GVA Inferior ganglion IX Tympanic nerve—middle ear, Visceralpharynx, tongue, carotid sinus sensation

GVE Salivatory nucleus Tympanic—lesser petrosal—otic Secretomotorganglion auriculotemporal to parotidgland

GSA Inferior ganglion IX External ear Cutaneoussensation

SVE Nucleus ambiguns Stylopharyngeus Swallowing

X Vagus GVE Dorsal motor Cardiac nerves and plexus, ganglia on Smoothnucleus X heart; pulmonary plexus, ganglia muscle and

respiratory tract; esophageal, gastric, glandsceliac plexus; myenteric andsubmucous plexus—to transversecolon

SVE Nucleus ambiguus Pharyngeal br., superior, inferior Swallowing,laryngeal nerves speaking

GVA Inferior ganglion X All fibers in all branches Visceralsensation

SVA Inferior ganglion X Br. to epiglottis, base of tongue, Tastetaste buds

GSA Superior ganglion X Auricular br.—ear, meatus Cutaneoussensation

XI Accessory SVE Nucleus ambiguus Communication to vagus—muscles Swallowing,of pharynx and larynx speaking

SVE Upper spinal cord—lat. Spinal portion—sternocleidomastoid, Movement,(Assuming column trapezius head andbranchiomeric shoulderorigin)

XII Hypoglossal GSE Nucleus XII Brs. intrinsic, extrinsic muscles of Tonguetongue movement

Table 18-1 Cranial Nerves

GP, general proprioception; GSA indicates general somatic afferent; GSE, general somatic efferent; GVA, general visceral afferent; GVE, general visceral efferent;SP, special proprioception; SSA, special somatic afferent; SVA, special visceral afferent; SVE, special visceral efferent.

I. OLFACTORY NERVE

Summary Bite. SVA is the only modality carried bythe olfactory nerve.

Cell bodies of the olfactory nerve, the nerve ofsmell, are found in the olfactory mucosa situatedover the superior nasal concha. Axons of the olfac-tory nerve pass through the cribriform plate of theethmoid bone to terminate in the olfactory bulb,which is connected to the brain by the olfactory

tract, technically a part of the brain (Fig. 18-1 andTables 18-1 and 18-5).

II. OPTIC NERVE

Summary Bite. SSA is the only modality carried bythe optic nerve.

Cell bodies of the optic nerve, the nerve of sight, arelocated in the ganglionic layer of cells composing theretina. Axons of these cells are gathered into bundlesthat leave the bulb of the eye as the optic nerve, pass-ing posteriorly through the orbit to exit through theoptic foramen. Here the axons join the optic nerve ofthe opposite side, forming the optic chiasma. Optictracts continue from the chiasma to enter the base of

the brain near the cerebral peduncle (Fig. 18-2 andTables 18-1 and 18-5).

III. OCULOMOTOR NERVE

Summary Bite. GSE, GVE, and GP (general propri-oception to the extraocular muscles for kinesthetic

sense) are the modalities carried by the oculomotor nerve.

The oculomotor nerve serves all of the extrinsic mus-cles of the eye, excluding the superior oblique andthe lateral rectus muscles, with general somatic effer-ent innervation. A specialized group of autonomicmotor cells in the oculomotor nucleus within thebrain is termed the Edinger–Westphal nucleus. Theseare preganglionic parasympathetic neurons whose

fibers are destined for the ciliary ganglion within theorbit. Postganglionic fibers from the ciliary ganglionpass to the orb via short ciliary nerves and on to theciliary body and sphincter pupillae muscles of theeye (see Table 18-2).

The oculomotor nerve exits the brain near themedial side of the cerebral peduncle, passes throughthe free and attached borders of the tentorium cere-belli, and then passes through the lateral wall of thecavernous sinus to enter the superior orbital fissurefor distribution. While in the cavernous sinus, contri-butions from the carotid plexus are communicated tothe oculomotor nerve. These communications arethe postganglionic sympathetic fibers from the supe-rior cervical ganglion destined for the dilatator pupil-lae muscle of the eye.

Once in the orbit, the oculomotor nerve dividesinto superior and inferior divisions, facilitating inner-vation of the extraocular muscles. The ciliary ganglion


Anosmia results following a unilateral lesion eitherwithin the olfactory epithelium or within the olfactorynerve, causing the patient to experience complete loss of

the sense of smell on the side ofthe lesion.

Anosmia


Figure 18-1. I. Olfactory nerve.


Changes in the longitudinal dimension of the optical axiswill cause images to be focused either anterior (myopia)or posterior (hyperopia) to the retina. This is usually theresult of changes in the refractive elements of the eye,notably the cornea, which experiences a slight change inshape. There may also occur an alteration in the dimen-sion of the orb. Often, both processes occur as a func-tion of aging. These conditions can be diagnosed andtreated with prescription-ground glasses that can opti-cally correct for the alteration in the longitudinal dimen-sion of the optical axis.

Multiple Sclerosis (MS)

Multiple sclerosis is one of the demyelinating diseasesthat affects the optic nerve but not the other cranialnerves. This is because the myelin surrounding the opticnerves is produced by glial cells rather than by Schwanncells, as in other cranial nerves.

Detached Retina

The 10-layered retina is loosely attached to the choroidlayer of the orb and is retained in that position by the

vitreous body. Sudden jolts ab-sorbed in the orbit may detachthe retina, causing a medicalemergency. The detached retina is sightless but sightcan usually be restored by surgical reattachment ofthe retina.

Cataract

Cataract is an age-related condition where the lens losesits transparency and becomes clouded, causing blurredvision. It is the major cause of poor vision and blindnessthroughout the world. Modern techniques now permitsurgical placement of plastic lenses, resulting inrestored vision.

Presbyopia

Presbyopia is associated with aging. It results fromthe inability of the eye to focus on close objects (ac-commodation), which is related to the lens becomingless elastic, thus light cannot be focused properly onthe retina.

Myopia and Hyperopia


Figure 18-2. II. Optic nerve. Observe the crossing over of fibers at the optic chiasma.

is suspended from the inferior division by theparasympathetic motor root of the ganglion.Additional communications to the ganglion are fromthe nasociliary nerve, a branch of the ophthalmic divi-sion of the trigeminal nerve. These communicationsare purely sensory, passing through the ganglion with-out synapsing there. Thus, these somatic sensorynerves reach their destination in the orb by way of theshort ciliary nerves. Postganglionic sympathetic fibersmay also communicate with the ganglion in a fashionsimilar to that of the nasociliary nerve; however,

these sympathetic fibers are destined for the dilatatorpupillae muscle. The functions of these intrinsic mus-cles of the eye are detailed in Chapter 10.

Proprioceptive fibers of the extraocular musclesare carried in the oculomotor nerve, then transmittedto the ophthalmic division of the trigeminal nerve tojoin it in the orbit, or via communications while itpasses through the walls of the cavernous sinus.Terminations of these fibers are described in the sec-tion on the trigeminal nerve (Fig. 18-3 and Tables 18-1, 18-2, and 18-5).


Preganglionic Parasympathetic Postganglionic Parasympathetic

Cranial Trigeminal Target:Nucleus of Nerve Preganglionic Parasympathetic Nerve Delivery SmoothOrigin of Origin Nerve Ganglion Association Nerve Muscle, Gland

Edinger- Oculomotor Unnamed Ciliary (GVE) Ophthalmic Short ciliary SphincterWestphal III (V1) from ganglion pupillae,

ciliary body

Super Facial VII Greater Pterygopalatine Maxillary Zygomatico- Lacrimal glandsalivatory petrosal (GVE) (V2) temporal to

lacrimal of (V1)

Superior Facial VII Greater Pterygopalatine Maxillary Greater; lesser Mucous glandssalivatory petrosal (GVE) (V2) palatine; post. of nasal

sup. nasal, cavity, max,nasopalatine; sinus, andpost., middle, palateant. sup.alveolars

Superior Facial VII Chorda Submandibular Mandibular Lingual Submandibularsalivatory tympani (GVE) (V3) and sublingual

glands, minorglands in floorof mouth

Inferior Glosso- Lesser Otic (GVE) Mandibular Auriculotemporal Parotid glandsalivatory pharyngeal petrosal (V3)

IX

Table 18-2 Parasympathetic Ganglia of the Head

GVE indicates general visceral efferent.

Injury to the oculomotor nerve will result in palsy on theipsilateral side with dilated pupil and ptosis. Additionally,the bulb of the eye will turn down and out with a con-

comitant inability to move theeye either up or down; moreover,the pupillary reflex will be lost.

Oculomotor Nerve Injury



IV. TROCHLEAR NERVE

Summary Bite. GSE and GP (general propriocep-tion fibers to the extraocular muscle for kinesthetic

sense) are the modalities carried by the trochlear nerve.

The trochlear nerve, the smallest of the cranialnerves, supplies the superior oblique muscle of theeye with motor innervation. This is the only cranialnerve originating on the dorsal surface of the brain-stem. From there, it passes around the midbrain topierce the tentorial dura, thus entering the cavernoussinus. While coursing through the wall of the cav-ernous sinus, the trochlear nerve communicates withthe carotid plexus and the ophthalmic division of thetrigeminal nerve. Proprioceptive fibers from the su-perior oblique muscle are thought to communicatewith the ophthalmic nerve at that point. On entering

the orbit through the superior orbital fissure, thenerve terminates in the superior oblique muscle,which it provides with motor innervation (Fig. 18-3and Tables 18-1 and 18-5).

V. TRIGEMINAL NERVE

Summary Bite. GSA, SVE, and GP (general propri-oception fibers to the muscles of mastication for

kinesthetic sense) are the modalities carried by the trigemi-nal nerve.

The largest of the cranial nerves, the trigeminalnerve serves much of the face, the teeth and support-ing structures, most of the anterior portion of the oralcavity, and the mucous membranes of the head withcutaneous sensation. Also, it provides motor innerva-

Figure 18-3. III. Oculomotor nerve. IV. Trochlear nerve. VI. Abducens nerve. Observe that thetrochlear and abducens nerves innervate only one muscle each. Note the ciliary ganglion and the distri-bution of the postganglionic parasympathetic fibers from it.

The trochlear nerve provides motor innervation only tothe superior oblique muscle. When this cranial nerve isinjured, the superior oblique muscle on the ipsilateral

side will be paralyzed, causingthe eyeball to rotate outward,resulting in double vision.

Trochlear Nerve Injury


tion to the muscles of mastication. The nerve has tworoots emanating from the pons. The larger, sensoryroot, which lies lateral to the motor root, contains thecentral processes of the neurons whose cell bodiesare found in the trigeminal (semilunar) ganglion, thesensory ganglion of the trigeminal nerve. This gan-glion is located under the cover of the dura in apocket (the Meckel cave) on the trigeminal impres-sion located near the apex of the petrous portion ofthe temporal bone. Peripheral processes of the sen-sory neurons located in the flat, semilunar-shapedganglion are gathered in three separate bundles.These bundles leave the ganglion as the ophthalmic,maxillary, and mandibular divisions of the trigeminalnerve. The motor root courses beneath the trigeminalganglion, proceeds medial to the sensory root, andthe two leave the skull via the foramen ovale andthen join each other to form the mandibular divisionof the trigeminal nerve. Thus, the mandibular divi-sion is mixed in function. The ophthalmic and maxil-lary divisions are purely sensory, and they leave thecranial vault via the superior orbital fissure and fora-men rotundum, respectively.

The four parasympathetic ganglia of the head arein close association with the trigeminal nerve, al-though, functionally, these ganglia are not part of the

trigeminal nerve. Postganglionic parasympatheticfibers arising in these ganglia are transmitted to thestructures they serve by joining branches of thetrigeminal nerve for distribution. The parasympa-thetic ganglia, the preganglionic motor root, and theassociated divisions of the trigeminal nerve are listedin Table 18-2 (Figs. 18-4 through 18-7 and Tables 18-1and 18-3 through 18-5).

OPHTHALMIC NERVE V1

Summary Bite. GSA is the only modality carried bythe ophthalmic division of the trigeminal nerve.

The ophthalmic nerve supplies the bulb and conjunc-tiva of the eye, the lacrimal gland, the skin of the fore-head and nose, and the mucous membranes of theparanasal sinuses with sensory innervation. The oph-thalmic nerve leaves the superior aspect of thetrigeminal ganglion, then lies in the lateral wall of thecavernous sinus as it courses to the orbit (Fig. 18-4 andTables 18-3 and 18-5). Along the way, tentorialbranches are supplied to the tentorium. Just before


Figure 18-4. V. Trigeminal nerve, ophthalmic division. Note the communications to the ciliary gan-glion from the nasociliary nerve.


Figure 18-5. V. Trigeminal nerve, maxillary division.

Figure 18-6. Pterygopalatine ganglion and connections.

entering the orbit through the superior orbital fissure,the nerve divides into three separate nerves: thelacrimal, frontal, and nasociliary nerves. In its course,the ophthalmic nerve communicates with the carotidplexus in the cavernous sinus and with other cranialnerves represented in the orbit. However, discussionof these communications is not warranted here.

Lacrimal Nerve

The lacrimal nerve, the smallest branch of the oph-thalmic division, runs along the lateral rectus muscledistributing to the lacrimal gland and adjacent con-junctiva. It then exits the orbit to be distributed to theskin of the lateral aspect of the upper eyelid (Fig. 18-4). While in the orbit, it communicates with the zy-gomaticotemporal branch of the zygomatic nerve ofthe maxillary division of the trigeminal nerve, which iscarrying postganglionic parasympathetic fibers com-municated to it from the pterygopalatine ganglion.

These parasympathetic fibers are then transmitted tothe lacrimal gland via the lacrimal nerve, thus provid-ing it with secretomotor innervation (see Table 18-2).

Frontal Nerve

The frontal nerve, the largest branch of the oph-thalmic nerve, divides shortly after entering the supe-rior aspect of the orbit into a smaller supratrochlearand a larger supraorbital nerve. The former passesmedial to the latter as the nerves course anteriorlyabove the levator palpebrae superioris muscle (Fig.18-4). The supratrochlear nerve bends to pass supe-rior to the pulley of the superior oblique muscle.Here it provides sensory innervation to the conjunc-tiva and skin of the medial aspect of the upper eyelidbefore leaving the orbit to turn upward to supply theskin over the forehead. The supraorbital nerve con-tinues forward to exit the orbit at the supraorbitalnotch. While passing the notch, it sends a filament


Posterior division ofmandibular nerve

Figure 18-7. V. Trigeminal nerve, mandibular division. Observe the chorda tympani from the facialnerve joining the lingual nerve.


Division of AssociatedTrigeminal Nerve Foramen of ParasympatheticNerve Modality Branch(es) Passage Ganglion/Nerve Sensory Region Served

Ophthalmic GSA Lacrimal Exits Zygomaticotemporal Lacrimal gland, adjacent(V1) Superior of V2, delivers post. conjunctiva, lateralaspect

orbital para. from pterygo- of skin of upper eyelidfissure palatine ganglion

(VII) for lacrimalgland (GVE)

Frontal ExitsSuperiororbital fissure

Supratrochlear Conjunctiva and skin ofthe medial portion of theeye and skin over theforehead

Supraorbital Filament to frontal sinus,upper eyelid, forehead,and scalp

Nasociliary Exits Superior Ciliary ganglion (III)orbital fissure & possibly post. sym.

from carotid plexus(GVE) (Postganglionicsympathetic todilatator pupillae)

Long ciliary Orb, corneaPosterior P.E. foramen—ethmoidal,ethmoidal sphenoidal, frontal

sinusesAnterior A.E. foramen—ethmoidal,ethmoidal sphenoidal, frontal

sinusesInternal nasal Mucous membranesExternal nasal Ala and globus of noseInfratrochlear Conjunctiva, eyelid,

caruncula, lacrimal sac,side of nose

Maxillary GSA Zygomatic Exits Rotundum Pterygopalatine(V2) ganglion (VII)

delivers post. para.secretomotor fibersto zyygomatico-temporal nerve fordistribution tolacrimal nerve tolacrimal gland (GVE)

Zygomaticofacial Skin of the cheekZygomatico- Delivers secretomotor Skin of temporal regiontemporal fibers to lacrimal

nerve for lacrimalgland

Maxillary (V2) GSA Pterygopalatine These nerves serve as a functional connection to the pterygopalatineganglion permitting passage of post. para. to zygomatic nerve andsensory fibers from maxillary through ganglion to become other namedbranches of the maxillary nerve

Orbital Enters Inferior Periorbita, ethmoid, andorbital fissure sphenoid sinuses

Table 18-3 Trigeminal Nerve—Sensory Components

(continued)



Greater Exits Greater Pterygopalatine Adjacent soft palate, hardpalatine palatine ganglion (VII) palate, gingiva, mucous

delivers post. para. membranes anteriorly tosecretomotor fibers to incisor teeth (communi-small glands of the cates with nasopalatine)nasal cavity, pharynx,and palate (GVE)

Lesser palatine Exits Lesser Delivers secretomotor Soft palate, tonsil, andpalatine fibers to glands of soft uvula. (Many of the affer-

palate ents were communicatedfrom facial nerve)

Posterior Exits Delivers secretomotor Nasal cavity supplyingsuperior nasal Sphenopalatine fibers to glands of mucous memb. of sup.branches nasal cavity and middle conchae,

median nasal septum andethmoid sinus. Majortrunk is nasopalatine

Nasopalatine Exits Incisive Delivers secretomotor Between septum andcanal fibers to glands of mucous memb. to incisive

nasal cavity canal. Serves anteriorpalate as far laterally ascuspid. (Communicateswith greater palatinenerve)

Pharyngeal br. Enters Delivers secretomotor Enters pharyngeal canal.Pharyngeal fibers to glands of Serves m. memb. andcanal nasopharynx and nasopharynx to auditory

spheniod sinus tubePosterior Enters Poster Sometimes branched.superior or superior Passes over max.alveolara alveolar tuberosity to serve m.

memb. of cheek andadjacent gingiva. EntersP.S.A.F to distribute tomax. sinus and to roots of 3 max. molars (exceptmesial buccal root of 1st molar)

Maxillary GSA Infraorbital This nerve is a continuation of the maxillary nerve into the floor of the(V2) orbit via the inferior orbital fissure and exiting the skull at the

infraorbital foramenMiddle Lateral wall of max.sinus,superior alveolara enters mesial buccal root

of 1st molar and all rootsof premolars

Anterior Anterior max. sinus, andsuperior alveolara roots of anterior teeth,

and twigs to floor of nasal cavity serving inferiormeatus, and adjacent m.membrane

Inferior Exits Infraorbital Skin and conjunctiva ofpalpebral brs. the lower eyelidExternal Exits Infraorbital Skin about the lateralnasal brs. aspect of the nose

Table 18-3 Trigeminal Nerve—Sensory Components (continued)

(continued)



Superior Exits Infraorbital Skin and mucous memb.labial brs. of the upper lip

Mandibular GSA Sensory root Exits Ovale Sensory and motor roots join outside the skull (F.(V3) ovale) to form a mixed nerve. Some branches are

sensory, some motor, whereas some are mixedFrom trunk Enters Dura and mastoid air cellsRecurrent Spinosummeningeal

From anterior Skin of cheek overdivision Buccal buccinator muscle passes

through buccinatormuscle to serve buccalmucosa and adjacentgingiva. (May communicate with facial nerve fordistribution purposes)

Articular br. to TMJTMJ From:masseteric nerveb

From posterior Joined by chorda Anterior 2/3 of tonguedivision Lingual tympani (VII) delivering with GSA and delivers

taste fibers (SVA) to SVA (taste) from facialant. 2/3 of tongue, and nerve to taste buds inpre. para to anterior 2/3 of tongue.submandibular Post.para fromganglion (VII) delivers submandibular ganglionpost.para from pass directly toganglion to submandibular gland.sublingual and minor Those destined forsalivary glands of the sublingual gland andfloor of the mouth other minor glands(GVE) reenter the lingual and

get distributed to theglands.

Inferior Enters Mandibular teeth andalveolar Mandibular supporting tissues via a

dental plexus, twoterminals—main trunkcontinues to incisor teeth,other terminal is mentalnerve

Mental Exits Mental Skin of chin, lower lipincluding mucousmembrane

Auriculo- Otic ganglion (IX) Distribute superficialtemporal communicates post. temporal nerves over skin

para fibers for of temple. Articular brs.distribution to the toTMJ secretomotorparotid gland (GVE) fibers from otic ganglion

to parotid gland

Table 18-3 Trigeminal Nerve—Sensory Components

GSA indicates general somatic afferent; GVE, general visceral efferent; TMJ, temporomandibular joint.aPosterior, middle, and anterior superior alveolar nerves communicate, forming a dental plexus before innervating the teeth.bThe masseteric nerve from the anterior division is a mixed nerve. Its sensory fibers are the articular branches to the TMJ.


Division ofTrigeminal Nerve Modality Nerve Branch Motor to Muscles

Mandibular (V3) SVE Sensory and motor roots of the trigeminal nerve exit the foramenovale and then join to form the trunk of the nerve, which then dividesinto anterior and posterior divisions. Some nerves are sensory, somemotor, and some mixed. Only motor components are presented.

From TrunkNerve to medial pterygoid Medial pterygoidNerve to tensor tympani Tensor tympaniNerve to tensor veli palatini Tensor veli palatini

From Anterior DivisionDeep temporal nerves Temporalis(anterior and posterior)Lateral pterygoid nerve Lateral pterygoidMasseteric nerve Masseter

From Posterior DivisionMylohyoid nerve MylohyoidNerve to anterior digastric Anterior diagastric

Table 18-4 Trigeminal Nerve—Motor Components

SVE indicates special visceral efferent.

into the frontal sinus. The nerve supplies sensory in-nervation to the upper lid, forehead, and scalp as farposteriorly as the lambdoidal suture.

Nasociliary Nerve

The nasociliary nerve enters the orbit between thelateral rectus muscle and the oculomotor nerve. Itthen passes obliquely over the optic nerve to the me-dial wall of the orbit, where its terminal branch en-ters the anterior ethmoidal foramen (Fig. 18-4). Justbefore entering the foramen, the nasociliary nervegives off an infratrochlear branch, which courses an-teriorly along the medial wall of the orbit and exits atits medial margin. Along the way, the branch pro-vides sensory innervation to the conjunctiva, eyelid,lacrimal sac, caruncula, and side of the nose. Anterior

and posterior ethmoidal branches enter the same-named foramina to supply the ethmoidal, sphenoidal,and frontal sinuses. The anterior ethmoidal nerve

continues through the ethmoid bone to enter thenasal cavity. Internal nasal branches arising from itinnervate the mucous membranes of the nasal cavity.The anterior ethmoidal nerve continues anteriorly toexit the nasal cavity at the inferior border of the nasalbone as the external nasal branch, providing generalsensation to the ala and globe of the nose.

While in the orbit, the nasociliary nerve sendslong ciliary nerves to the eyeball as the nerve crossesthe optic nerve. Other short filaments pass to the cil-iary ganglion, establishing a close association with

this parasympathetic ganglion. The long ciliarynerves and those filaments that pass to the ganglionand on to the eyeball, as part of the short ciliarynerves are purely sensory and are destined for theiris and cornea. Postganglionic sympathetic fiberscommunicate to the ophthalmic nerve from thecarotid plexus while passing through the cavernoussinus, or they may accompany the long ciliary nervesor the short filaments to the ganglion and on to theeyeball via the short ciliary nerves. These postgan-glionic sympathetic fibers are destined for the dilata-tor pupillae muscle within the iris.

Maxillary Nerve V2

Summary Bite. GSA is the only modality carried bythe maxillary division of the trigeminal nerve.

The maxillary nerve, the second division of thetrigeminal nerve, is purely sensory and serves theskin of the side of the nose; cheek; eyelids; mid-face;nasopharynx; tonsil; palate; maxillary sinus; and gin-giva, teeth, and associated structures of the upperjaw. The nerve exits the cranial vault via the foramenrotundum after passing through the posterior portionof the cavernous sinus. From the foramen rotundum,the nerve courses through the pterygopalatine fossato enter the floor of the orbit at the inferior orbital fis-sure. Here, the nerve becomes known as the infraor-bital nerve, enters the infraorbital canal, and then


Cranial Nerve Modality Assessment Technique Perceived Dysfunction

I Olfactory SVA Patient is asked to differentiate distinct Damage such as an ethmoid fractureodors (coffee, vanilla) with eyes covered. may result in anosmia (loss of senseTest each side independently. of smell).

II Optic SSA Eye charts are used to assess visual acuity. Damage to the retina usually resultsVisual fields are determined by examining in blindness to the affected eye.when patient observes an object moving Damage beyond the optic chiasmafrom lateral to medial. Ophthalmoscope will present partial visual losses.used for observing retina, optic disc,and blood vessels.

III Oculomotor GSE Patient is asked to follow with his or her Damage to this modality may causeeyes the examiner’s finger as it moves up paralysis of all extraocular musclesand down vertically and medially and except the superior oblique andlaterally. Watch for crossing of eyes during lateral rectus. This produces lateralconvergence. strabismus and inability to look

vertically. Also ptosis (eyelid drooping).GVE Examine patient for pupillary reflex with Damage to this modality will produce

light shining on and off in each eye. lack of pupillary reflex, dilated pupils,Observe and compare contractions and and lack of changes in pupil at closedilations in affected and unaffected eyes. focus.

IV Trochlear GSE Analysis of function is performed during Damage to this nerve causes double testing of the oculomotor nerve. vision and inability to rotate the eye

inferolaterally.

V Trigeminal GSA Test for corneal reflex with whisp of cotton. Damage to this division will inhibit theOphthalmic Prick forehead with pin (pain), apply warm corneal reflex and will reduce or inhibitdivision (V1) and cold objects (temperature). sensation over the (V1) zone.

Maxillary GSA Stroke sensory zone of (V2) with eyes Damage to this division will reduce ordivision (V2) closed (light touch), prick with pin (pain), inhibit sensation over the (V2) zone.

apply warm and cold objects (temperature).Mandibular GSA Stroke sensory zone of (V3) with eyes Damage to this division will reduce ordivision (V3) closed (light touch), prick with pin (pain), inhibit sensation over the (V3) zone.

apply warm and cold objects (temperature).Mandibular SVE Ask patient to clench jaws, open, then move Damage in this modality may causedivision (V3) jaw side to side with resistance. Muscle paralysis of the muscles of mastication,

strength in the temporalis and masseter thus causing the jaw to deviate sameshould be compared from side to side by side as the lesion.palpation.

VI Abducens GSE Analysis of function is performed during Damage to this nerve causes doubletesting of the oculomotor nerve. vision and paralysis of the lateral

rectus muscle, thus the eye remainsrotated medially on the affected side.

VII Facial SVA Test for taste for sweet and salty on anterior Damage to this modality will reduce or2/3 of tongue. inhibit the sensation of taste on the

anterior 2/3 of the tongue.GVE Observe tearing with pungent fumes Damage to this modality will reduce or

(ammonia). inhibit the ability to secrete tears fromthe affected side. Mucus production inthe nasal cavity and salivary glandsecretions from the submandibular and sublingual glands is more difficult toevaluate.

Table 18-5 Cranial Nerves—Clinical Testing

(continued)


Cranial Nerve Modality Assessment Technique Perceived Dysfunction

SVE Observe symmetry of face when asked to Damage to this modality, such as inclose eyes, frown, smile, whistle, raise stroke, causes a paralysis of theeyebrows. Look for flacid sagging of face. muscles of facial expression, which

causes the face to sag and an inabilityto make facial expressions on theaffected side.

VIII SSA Test with a tuning fork by air and bone Loss of hearing by air conductionVestibulocochlear conduction. indicates a lesion or damage to theCochlear division middle ear. Loss by bone conduction

indicates nerve deafness.Vestibular division GSA (SP) Test walking a straight line, dizziness. Damage to the vestibular division elicits

Watch for rapid eye movements. dizziness, nausea, vomiting, anduncontrolled rapid eye movement.

IX GVA Test for gag reflex and swallowing and Damage to this modality would reduceGlossopharyngeal position of the uvula during this procedure. or inhibit the gag reflex and produce

Test touch reception on the posterior 1/3 of difficulty in swallowing. It would alsothe tongue.b reduce or inhibit general sensation on

the posterior 1/3 of the tongue.Sensation to the carotid body and sinuswould also be lost, thereby alteringblood pressure and oxygen tension inthe bloodstream.

SVA Test for bitter and sour taste on the posterior Damage to this modality would reduce1/3 of the tongue and on circumvallate or inhibit the sense of taste over thepapillae. posterior 1/3 of the tongue and on the

circumvallate papillae.GVE Observe saliva flow from the parotid duct. Damage to this modality would reduce

or inhibit saliva secretion from theparotid gland.

X Vagusc SVE Have patient elevate the palate by saying Damage to this component will prevent“aahhhh,” swallow, and speak. the palate from being elevated and

will make swallowing and speechdifficult.

XI Accessoryd SVE Have patient shrug shoulders and rotate Damage to this modality would reducehead against resistance. or inhibit the movement of the head

and shoulders.

XII Hypoglossal GSE Have patient protrude and retract tongue. Damage to this nerve will cause thetongue to deviate toward the affectedside on protrusion, and that side willappear shrunken and wrinkled.

Table 18-5 Cranial Nerves—Clinical Testing (continued)

GSA, general somatic afferent; GSE, general somatic afferent; GVE, general visceral efferent; SP, special proprioception; SSA, special somatic afferent; SVAindicates special visceral afferent; SVE, special visceral efferent.aNote that some modalities associated with certain cranial nerves are not represented in this table because some areas of the head and neck receive overlap-ping innervation from more than one cranial nerve, thus complicating definitive testing. For example the area about the ear/auditory meatus receives sensoryinnervation from several cranial nerves in addition to contributions from the cervical plexus, thereby making assessment extremely difficult.bBecause there is close association and intermingling of nerve fibers of the glossopharyngeal, vagus, and accessory nerves, it is difficult to distinguish the af-fected nerve in clinical testing procedures. However, the gag reflex is generally considered the definitive test for glossopharyngeal nerve damage.cAlthough the vagus nerve serves visceral structures in the thorax and abdomen, the contents of the table are restricted to its functions in the head and neck.dThis assumes that the SVE component of the accessory nerve that serves the sternocleidomastoid and trapezius muscles is from the cranial root of the ac-cessory nerve. Remember that the SVE component of the vagus is also part of the cranial root of the accessory nerve. Therefore, damage to this root wouldaffect both areas served by the vagus and the accessory nerves.


exits on the face through the infraorbital foramen(Figs. 18-5 and 18-6 and Tables 18-3 and 18-5).

Along its route, the maxillary nerve provides sev-eral branches in the cranial vault, pterygopalatinefossa, and orbit, as well as on the face. While in thecranial vault, its middle meningeal nerve supplies thedura. Several branches also arise from the nerve as ittraverses the pterygopalatine fossa.

Zygomatic Nerve

The zygomatic nerve, the first branch to arise from themaxillary nerve while it traverses the pteryogpalatinefossa, passes into the orbit and divides into the zygo-

maticofacial and zygomaticotemporal nerves. Both ofthese nerves enter the zygomatic bone and exit itthrough the like-named foramina on its external sur-face (Fig. 18-5). The zygomaticofacial nerve exits onthe face, providing sensation for the cheek. The zygo-maticotemporal nerve exits in the temporal fossa todistribute to the skin of the side of the forehead. Beforeleaving the orbit, the zygomaticotemporal nerve sup-plies a branch to the lacrimal nerve. This communica-tion is a postganglionic parasympathetic fiber derivedfrom cranial nerve VII, passed to the zygomatic nervefrom the pterygopalatine ganglion (see Table 18-2).The pterygopalatine ganglion lies in close associationwith the maxillary nerve within the pterygopalatinefossa and is connected to it via two pterygopalatine

nerves (Fig. 18-6).

Pterygopalatine Nerves

The pterygopalatine nerves are part of the maxillarynerve rather than part of the pterygopalatine gan-glion, although they serve as functional communica-tions to the ganglion by permitting the passage ofpostganglionic parasympathetic fibers from the gan-glion to the nerve trunk for distribution to thelacrimal gland (Fig. 18-6 and Table 18-2).

Additional postganglionic parasympathetic fibersare communicated from the pterygopalatine ganglionto branches of the maxillary nerve destined for glandsin the palate and nasal cavity, where these parasym-pathetic fibers serve secretomotor function.

There are several branches of the maxillarynerve that appear to originate from the ganglion butactually are branches of the two pterygopalatinenerves. These branches emerge after the pterygopala-tine nerves have passed through the ganglion. Theyare the orbital, palatine, posterior superior nasal, andpharyngeal branches.

Orbital BranchesThe orbital branches enter the orbit to supply theperiorbita and the posterior ethmoidal and sphe-noidal sinuses.

Greater Palatine NerveThe greater palatine nerve leaves the ganglion toenter and descend in the pterygopalatine canal, fi-nally to emerge on the palate through the greaterpalatine foramen (Fig. 18-6).

The greater palatine nerve serves the anteriorborder of the soft palate, hard palate, gingiva, andmucous membranes of this region as far anteriorly asthe incisive teeth, where it communicates with thenasopalatine nerve.

In its descent in the pterygopalatine canal, pos-

teroinferior nasal branches are given off, innervat-ing the inferior concha and the middle and inferiormeatuses.

The greater palatine nerve splits while in thecanal to form a lesser palatine nerve, which exits onthe palate through two or three like-named foraminaserving the soft palate, tonsil, and uvula (Fig. 18-6).

Many of the afferents to this region are from thefacial nerve communicated to the lesser palatinenerve through the pterygopalatine ganglion by way ofthe greater petrosal nerve and the nerve of the ptery-goid canal. These nerves are described with the fa-cial nerve.

Posterior Superior Nasal BranchesPosterior superior nasal branches enter the nasal cav-ity from the sphenopalatine foramen to supply themucous membrane over the middle and superiorconchae, the median nasal septum, and the eth-moidal sinus (Fig. 18-6).

One of these branches, the nasopalatine nerve, islarger than the others and continues anteriorly be-tween the median nasal septum and the mucousmembrane to reach the incisive canal, throughwhich it passes to communicate with its counterpartfrom the opposite side (Fig. 18-6). It serves the ante-rior palate as far posteriorly as the cuspid teeth,where it overlaps the distribution of the greater pala-tine nerve.

Pharyngeal BranchA pharyngeal branch leaves the posterior aspect ofthe ganglion to enter the pharyngeal canal. It servesthe mucous membrane and the nasopharynx as far asthe auditory tube (Fig. 18-6).

Posterior Superior Alveolar Nerve(s)Arising from the main trunk of the maxillary nerve,while still in the pterygopalatine fossa, is (are) theposterior superior alveolar nerve(s) (Fig. 18-5).

This nerve, which may display more than oneterminal, passes down over the tuberosity of the max-illa providing branches to the mucous membrane ofthe cheek and the adjacent gingiva.

The posterior superior alveolar nerve then entersthe same-named foramen to supply the maxillarysinus and the molar teeth, with the exception of themesial buccal root of the first molar. Sensory innerva-tion to this root is provided by the middle superioralveolar nerve, which is described in the next section.

Infraorbital NerveAfter traversing the pterygopalatine fossa, the maxil-lary nerve enters the floor of the orbit, thus becomingthe infraorbital nerve (Fig. 18-5).

On entering the floor of the orbit, the infraorbitalnerve sends a middle superior alveolar nerve over thelateral wall of the maxillary sinus, which it inner-vates. Branches of this nerve then enter the mesialbuccal root of the first molar and all of the roots of thepremolar teeth.

Continuing anteriorly, the infraorbital nerve pro-vides an anterior superior alveolar nerve just beforeits exit from the infraorbital foramen. The anterior

superior alveolar nerve supplies the anterior maxil-lary sinus and the roots of the anterior teeth. Also,small twigs of this nerve enter the nasal cavity to sup-ply its floor, the inferior meatus, and adjacent mu-cous membrane.

The posterior, middle, and anterior superior alve-olar nerves intermingle, forming a dental plexus be-fore innervating the upper teeth.

As the infraorbital nerve exits the skull via thesame-named foramen, it provides the following threemajor groups:

■ Inferior palpebral branches, ascending to the lowereyelid.

■ External nasal braches, serving the side of thenose.

■ Superior labial branches, serving the upper lip.

Mandibular Nerve V3

Summary Bite. GSA, SVE, and GP (general propri-oception fibers to the muscles of mastication kines-

thetic sense) are the modalities carried by the mandibulardivision of the trigeminal nerve.

The mandibular nerve, the largest division of thetrigeminal nerve, is the only division containing bothmotor and sensory components. The sensory fibersserve the skin about the lower face, cheek and lowerlip, ear, external acoustic meatus, temporomandibu-lar joint, and skin about the temporal region. Thissensory component also supplies the mucous mem-branes of the cheek, the mucosa of the anterior twothirds of the tongue, the mandibular teeth, and sup-

porting tissues and gingiva, mastoid air cells, themandible, and portions of the dura.

The motor component supplies all of the muscu-lature developed within the first pharyngeal arch: themuscles of mastication, including the temporalis,masseter, medial and lateral pterygoid muscles, aswell as the tensors tympani and veli palatini, and theanterior belly of the digastric and the mylohyoid mus-cles (Fig. 18-7 and Tables 18-3 through 18-5).

As described earlier, the motor and sensory rootsdo not unite before exiting the skull. Rather, bothroots pass through the foramen ovale and unite justoutside the skull, forming the mandibular trunk. Thelatter is a mixed nerve that soon divides into asmaller, anterior division that is primarily motor anda larger posterior division that is mostly sensory infunction.

Lying just outside the foramen ovale, immedi-ately deep to the mandibular nerve trunk, is the oticganglion. Although this parasympathetic ganglion(see Table 18-2) is in close association with themandibular nerve via the nerve to the medial ptery-goid muscle that passes through it, the preganglionicparasympathetic fibers synapsing within the ganglionare from the lesser petrosal nerve, a branch of theglossopharyngeal nerve.

Postganglionic fibers from the ganglion are secre-tomotor to the parotid gland and use the auriculotem-poral nerve for distribution. The mandibular nervepossesses several branches: some from the nervetrunk, others from the anterior division, and still oth-ers from the posterior division; they are described inthat order in the following sections.

Branches from the Mandibular Trunk

Two nerves branch from the trunk of the nerve: therecurrent meningeal nerve and the nerve to the me-dial pterygoid muscle.

The recurrent meningeal nerve leaves themandibular trunk and ascends back into the skullthrough the foramen spinosum in company with themiddle meningeal artery. This nerve supplies thedura, while some fibers supply the mastoid air cells.

The medial pterygoid nerve arises from the pos-terior aspect of the mandibular trunk, passes throughthe otic ganglion, and then enters the deep surface ofthe medial pterygoid muscle, supplying it with motorinnervation (Fig. 18-7).

Two small branches arise from the medial ptery-goid nerve: the nerve to the tensor tympani muscle,which penetrates the auditory tube cartilage to sup-ply this muscle with motor innervation, and thenerve to the tensor veli palatini muscle, which entersthat muscle near its origin, supplying it with motorinnervation.



Branches from the Anterior Mandibular Division

The smaller anterior division, through its branches,supplies all of the remaining muscles of masticationwith motor innervation (Fig. 18-7).

The buccal nerve is the only branch of the ante-rior division that is sensory in function. Arising fromthis division are the deep temporal, lateral pterygoid,masseteric, and buccal nerves.

The deep temporal nerves arise from the anteriordivision and ascend, usually as anterior and posteriorbranches, between the two heads of the lateral ptery-goid muscle to enter the deep surface of the temporalismuscle, which they supply. Frequently, the anteriorbranch arises from the buccal nerve, whereas the pos-terior branch may arise in common with the masse-teric nerve.

The lateral pterygoid nerve is very short andalmost immediately enters the deep surface of thelateral pterygoid muscle, which it serves. Thisnerve may originate from the buccal nerve as thatnerve passes between the two heads of the lateralpterygoid muscle.

The masseteric nerve passes above the lateralpterygoid muscle on its way to the mandibular notch,which it crosses to enter the masseter muscle in com-pany with the same-named artery; it gives off asensory twig to the temporomandibular joint beforeentering the muscle.

The origin of the buccal nerve (clinically some-times referred to as the long buccal nerve) is not con-stant. Occasionally, it may arise from the trigeminalganglion individually, reaching its destination via aseparate foramen. Alternatively, it may arise fromthe inferior alveolar nerve of the posterior division.The description that follows assumes origin from theanterior division. The buccal nerve ascends, passingbetween the two heads of the lateral pterygoid mus-cle. Here it may give off branches to the temporalisand/or the lateral pterygoid muscles. It then de-scends to ramify over the buccinator muscle, supply-ing sensory innervation to the skin of the cheek inthe area. Other branches pierce the muscle to providesensory fibers to the buccal mucosa and adjacent gin-giva. The buccal nerve communicates with the facialnerve, forming a complex over the buccinator mus-cle, presumably facilitating distribution of bothnerves. It should be remembered that the buccalnerve is purely sensory and does not innervate thebuccinator muscle (see the VII. Facial Nerve section).

Branches from the Posterior Mandibular Division

The larger posterior division of the mandibular nerveis mainly sensory in function, with the mylohyoidnerve being the only motor nerve of the division.Nerves arising from this division of the mandibular

nerve are the lingual, inferior alveolar, and auricu-lotemporal nerves (Fig. 18-7).

The lingual nerve descends deep to the lateralpterygoid muscle, then courses forward between themedial pterygoid muscle and the mandible, where itis joined by the chorda tympani nerve, a branch ofthe facial nerve. The lingual nerve then descendsover the superior pharyngeal constrictor and sty-loglossus muscles to reach the lateral aspect of thetongue adjacent to the hyoglossus muscle. Here it liesbetween that muscle and the submandibular gland.

The nerve proceeds anteriorly to the tip of thetongue, lying alongside the submandibular duct justbeneath the mucosa.

Fibers of the lingual nerve, derived from thetrigeminal nerve, provide sensory innervation to themucous membranes of the anterior two thirds of thetongue, the lingual gingiva, and other structures adja-cent to the tongue.

Fibers communicated to the lingual nerve fromthe facial nerve, via the chorda tympani, serve twofunctions:

■ One group provides special sensory fibers for tasteto the taste buds of the anterior two thirds ofthe tongue; these fibers are distributed by the lin-gual nerve.

■ The other group supplies preganglionic parasym-pathetic fibers destined for the submandibular gan-glion (see Table 18-2). The ganglion is suspendedfrom the lingual nerve as that nerve lies betweenthe hyoglossus muscle and the submandibulargland. Preganglionic fibers (contributed by thechorda tympani nerve) leave the lingual nerveto synapse on postganglionic cell bodies withinthe ganglion.

Postganglionic fibers pass directly to the sub-mandibular gland or reenter the lingual nerve for dis-tribution (as secretomotor fibers) to the sublingualgland and other minor salivary glands in the floor ofthe mouth.

The inferior alveolar nerve descends along with,but lateral to, the lingual nerve in company with theinferior alveolar artery on its way to the mandibularforamen.

The mylohyoid nerve arises from the inferioralveolar nerve just before the latter enters themandibular foramen. The mylohyoid nerve descendsin the mylohyoid groove on the mandible, then en-ters the mylohyoid muscle, which it provides withmotor innervation. A portion of this nerve continueson the superficial surface of the muscle to the ante-rior belly of the digastric muscle, supplying it withmotor innervation.

Upon entering the mandibular foramen, the infe-rior alveolar nerve proceeds in the bony mandibularcanal, forming a dental plexus that provides sensoryinnervation to the mandibular teeth and supportingstructures.

The nerve divides into two terminals: one, themental nerve, exits the mental foramen to providesensation to the skin of the lower lip and chin as wellas to the mucous membrane of the lower lip; theother, the incisive nerve, continues to supply the an-terior teeth and supporting tissues with sensory in-nervation.

The auriculotemporal nerve originates usuallyvia two rootlets that arise from the trunk of the pos-terior division. One rootlet passes deep, whereas theother passes superficial to the middle meningeal ar-tery, forming a loop around it, just prior to the arteryentering the foramen spinosum. The two rootletsthen unite, forming the auriculotemporal nerve,which courses deep to the lateral pterygoid muscle.

After emerging at the neck of the mandible, thenerve turns superiorly with the superficial temporalartery within the substance of the parotid gland. It con-tinues to ascend between the auricula and temporo-mandibular joint, exiting the gland to pass over the zy-gomatic arch to distribute sensory fibers as superficial

temporal nerves over the skin of the temporal region.In its course, the auriculotemporal nerve sends

articular branches to the temporomandibular joint,

anterior auricular branches to the anterior portion ofthe external ear, branches to the external acoustic

meatus, and branches to the parotid gland. Thosebranches to the parotid gland are postganglionicparasympathetic fibers whose cell bodies are locatedin the otic ganglion. These fibers, which supply secre-tomotor innervation to the gland, are communicatedto the rootlets of the auriculotemporal nerve from theotic ganglion for distribution to the parotid gland (seeTable 18-2).

Preganglionic parasympathetic fibers to the gan-glion are supplied by the lesser petrosal branch of theglossopharyngeal nerve.

Although the auriculotemporal nerve is strictlysensory, it and the facial nerve communicate freelyabout the parotid gland, each facilitating distribution.

VI. ABDUCENS NERVE

Summary Bite. GSE and GP (general propriocep-tion fibers to an extraocular muscle for kinesthetic

sense) are the modalities carried by the abducens nerve.

The abducens nerve arises from the brain betweenthe pons and the medulla. On its course to the orbit,the nerve pierces the dura covering the dorsum sel-


Lesion of the motor root of the trigeminal nerve of oneside results in ipsilateral flaccid paralysis and muscularatrophy of the muscles of mastication and all other mus-cles receiving motor supply from the mandibular divi-sion of the trigeminal nerve. Additionally, hyperacusis inone ear results from inactivity of the ipsilateral tensortympani muscle.

The ipsilateral general somatic afferent modality willresult in diminished sensation in the orofacial and nasalstructures.

Trigeminal Neuralgia

Trigeminal neuralgia (tic douloureux), an extremelypainful, debilitating condition involving pain fibers of the

trigeminal nerve, is caused by anunknown etiology but occasion-ally it may be associated with dental carious lesions. Thepain is often excruciating and is experienced over theface, teeth, gingivae, nasal, and paranasal cavities, aswell as the external ear canal. These are the areasserved by the maxillary and mandibular divisions, al-though infrequently the area served by the ophthalmicdivision of the trigeminal nerve may be affected.Treatment varies from alcohol injection into the trigemi-nal division affected to sectioning of the trigeminal nervebetween the pons and the ganglion.

Unilateral Lesion of the Motor Root of theTrigeminal Nerve



lae of the sphenoid bone and enters the cavernoussinus, where it receives communications from thecarotid plexus.

Upon entering the superior orbital fissure, thenerve courses to the lateral rectus muscle, supplying itwith motor innervation. This is the sole function of theabducens nerve (Fig. 18-3 and Tables 18-1 and 18-5).

VII. FACIAL NERVE

Summary Bite. SVE, GVE, SVA, GVA, and GSA arethe modalities carried by the facial nerve.

The facial nerve exhibits several modalities becauseits branches serve structures within the temporalbone, deep face, oral cavity, and the superficial face.The modalities carried by the facial nerve include:special visceral efferent, general visceral efferent,special visceral afferent, general visceral afferent,and general somatic afferent (Figs. 18-8 and 18-9 andTables 18-1, 18-2, and 18-5).

The components of the facial nerve and theirfunctions are as follows (see Fig. 18-8 and Tables 18-1, 18-2, and 18-5):

■ Special Visceral Motor component serves all of themuscles derived from the second pharyngeal arch,including the muscles of facial expression, the buc-cinator, platysma, and those of the scalp and exter-nal ear, the stapedius, posterior belly of the digas-tric, and stylohyoid muscles.

■ General sensory component supplies the externalacoustic meatus.

■ Visceral sensory component supplies the softpalate and some of the pharynx.

■ Special sensory component is for taste to the ante-rior two thirds of the tongue.

■ Parasympathetic component effecting secretomo-tor function is supplied to the lacrimal, nasal, pala-

tine, submandibular, and sublingual glands (seeTable 18-2).

The nerve possesses two roots, a large motor rootand a smaller root, termed the nervus intermedius,containing the special sensory fibers for taste,parasympathetic fibers, and general sensory fibers.The two roots emerge from the brain between thepons and the inferior cerebellar peduncle.

These roots enter the internal acoustic meatusalong with the vestibulocochlear nerve, but separatefrom it as the two roots enter the petrous portion ofthe temporal bone in a chamber of its own, the facial

canal (Fig. 18-9).Near the tympanic cavity, the facial nerve takes

an abrupt turn inferiorly to exit the skull through thestylomastoid foramen. Located at this turn where thetwo roots fuse is the geniculate ganglion, the sensoryganglion of the facial nerve (Fig. 18-8 and Table 18-1).

Several branches arise from the nerve as itcourses through the temporal bone, including thegreater petrosal nerve from the geniculate ganglion,the nerve to the stapedius muscle, and the chordatympani nerve.

Greater Petrosal Nerve

Arising from the geniculate ganglion is the greaterpetrosal nerve, which carries preganglionic parasym-pathetic fibers destined for the pterygopalatine gan-glion along with sensory fibers for the soft palate andpharynx (Tables 18-1 and 18-2). The facial nerveleaves the petrous portion of the temporal bone viathe hiatus of the facial canal near the foramenlacerum and then enters the pterygoid canal (vidiancanal) of the sphenoid bone. Here it is joined by thedeep petrosal nerve, a postganglionic sympatheticnerve arising from the carotid plexus whose cell bod-ies are located in the superior cervical ganglion. Thecombined nerve, known as the nerve of the pterygoid

canal (vidian nerve), passes through the same-namedcanal in the sphenoid bone to gain access to the

The abducens nerve provides motor innervation to thelateral rectus muscle. When affected, the muscle on theipsilateral side will be paralyzed, causing the eyeball to

deviate medially, resulting indouble vision.

Abducens Nerve Injury


pterygopalatine fossa, where it joins the pterygopala-tine ganglion.

Preganglionic parasympathetic fibers synapse onpostganglionic parasympathetic cell bodies housedwithin the pterygopalatine ganglion.

Fibers of these postganglionic parasympatheticneurons are communicated to nerves branching fromthe maxillary division of the trigeminal nerve for dis-tribution to the lacrimal gland, as well as to smallglands of the nasal cavity, pharynx, and palate.

The sympathetic component of the vidian nervedoes not synapse in the pterygopalatine ganglion; in-stead, these postganglionic fibers are distributed inthe same fashion as the postganglionic parasympa-thetic fibers.

The parasympathetic fibers are secretomotor infunction, whereas the sympathetic fibers functionmainly in vasoconstriction.

Some visceral sensory fibers from the geniculateganglion travel along with the greater petrosal nerveto be distributed ultimately by branches of the maxil-lary division of the trigeminal nerve to the area of thesoft palate via the lesser palatine nerve.

Nerve to the Stapedius Muscle

The nerve to the stapedius muscle, arising from thefacial nerve as it descends across the tympanum, pro-vides motor fibers to that muscle.

Chorda Tympani Nerve

The chorda tympani nerve arises from the facialnerve trunk just before the trunk’s exit from the sty-lomastoid foramen. The chorda tympani courses cra-nialward in a canal of its own, diverging away from


Figure 18-8. VII. Facial nerve.


the main nerve, bending to pass over the tympanicmembrane and across the manubrium of the malleus.It leaves the tympanic cavity to enter a canal in thepetrotympanic fissure, then exits the skull at thespine of the sphenoid bone. The chorda tympaninerve, which may receive a communication from theotic ganglion, joins the lingual branch of themandibular division of the trigeminal nerve for distri-bution. It contains special sensory fibers destined fortaste buds on the anterior two thirds of the tongueand preganglionic parasympathetic fibers destinedfor the submandibular ganglion (see Figs. 18-7 and 18-8 and Tables 18-1 and 18-2).

The submandibular ganglion, suspended by shortnerve filaments from the lingual nerve as it passesthe hyoglossus muscle, receives the preganglionicparasympathetic fibers of the chorda tympani nervevia the parasympathetic root (Fig. 18-7). Postganglionicparasympathetic fibers from the submandibular gan-glion pass to the submandibular gland or reenterthe lingual nerve to be distributed to the sublingualgland and minor salivary glands in the floor of themouth, providing them with secretomotor innerva-tion. Sympathetic stimulation of the salivary glands is accomplished by postganglionic sympathetic fibers

accompanying the arteries serving the glands.The function of this stimulation is generally to elicitvasoconstriction.

Beyond the origin of the chorda tympani nerve,the facial nerve exits the skull through the stylomas-toid foramen. There, it gives rise to the posterior au-ricular nerve and the nerves to the posterior digastricand stylohyoid muscles. It then passes into the retro-mandibular fossa to enter the substance of the parotidgland to form the parotid plexus.

Posterior Auricular Nerve

As the facial nerve exits the stylomastoid foramen,the posterior auricular nerve arises from it to passsuperiorly between the auricle and the mastoidprocess. It divides into occipital and auricularbranches after communicating with the auricularbranch of the vagus nerve and great auricular andlesser occipital nerves of the cervical plexus. The au-

ricular branch supplies motor innervation to the pos-terior auricular muscle of the ear and to some of itsintrinsic muscles. The occipital branch courses pos-teriorly to supply the occipitalis muscle with motorinnervation (Fig. 18-8).

Figure 18-9. VIII. Vestibulocochlear nerve. Note the nervus intermedius and motor portion of thefacial nerve accompanying the vestibular and cochlear divisions into the ear.

Nerve to the Posterior Belly of the

Digastric Muscle

The nerve to the posterior belly of the digastric mus-cle arises from the trunk of the facial nerve near thestylomastoid foramen and enters the muscle near itsmidbelly, providing it with motor innervation(Fig. 18-8).

Nerve to Stylohyoid Muscle

The nerve to the stylohyoid muscle arises from thefacial nerve in a similar fashion to or in common withthe nerve to the posterior digastric. The nerve to thestylohyoid muscle then enters the muscle at mid-belly, providing it with motor innervation (Fig. 18-8).

Parotid Plexus

After entering the parotid gland, the facial nerve di-vides into temporofacial and cervicofacial divisions,which form the parotid plexus. From there emergethe branches supplying motor innervation to themuscles of facial expression. These terminalbranches are named for the regions they supply, usu-ally dividing into five major branches from theplexus: temporal, zygomatic, buccal, mandibular, andcervical branches (Fig. 18-8). Space does not permit arepeat of the complete descriptions of each branch’sdistribution or of the muscles served by each branch,other than to state that, generally, the branch servesfacial muscles originating in the area of the nervebranch. The interested reader is referred back toChapter 8 for a discussion of the distribution of thebranches of the parotid plexus.

Note that branches of the facial nerve communi-cate freely with all of the terminal branches of thetrigeminal nerve. These communications, for exam-ple, those between the auriculotemporal nerve andthe facial nerve, apparently serve to facilitate distri-bution of the sensory branches of the trigeminalnerve about the face.

VIII. VESTIBULOCOCHLEAR NERVE

Summary Bite. SSA and SP (special proprioceptionwithin the vestibular mechanism for body balance)

are the modalities carried in the vestibulocochlear nerve.

The nerve of hearing and balance, the vestibulo-cochlear nerve, is composed of two separate sets offibers. The vestibular nerve for balance and thecochlear nerve for hearing are joined as a commonnerve entering the internal acoustic meatus with thefacial nerve (Fig. 18-9).

These two cranial nerves separate after enteringthe meatus as the vestibulocochlear nerve ap-proaches the area of its destination within the innerear. The vestibulocochlear nerve divides, sending thecochlear nerve into the laterally oriented cochlear ap-paratus and the vestibular nerve medially into thevestibular apparatus.

Cochlear Nerve

The cochlear nerve has its peripheral processes in theorgan of Corti, located in the membranous labyrinth,


Damage to the facial nerve (or its accidental analgesiaduring dental procedures) results in paralysis of themuscles of the affected side. Damage may occur duringsurgical involvement of the parotid gland, infection ofthe middle ear, knife wounds, or at birth during forcepsdelivery. Paralysis of the facial muscles results in ptosisof the eye (upper eyelid drooping); depression of thecorner of the mouth with accompanying oozing ofsaliva; speech disorder (especially involving labial

sounds); lack of muscle tone;and a sagging, distorted face.Bell palsy affects all of theipsilateral muscles about the face as well as othermuscles that developed from the second pharyngealarch. Because of this fact, patients affected with Bellpalsy have hyperacusis (loss of corneal blink) aswell as loss of taste from the ipsilateral side of theanterior tongue.

Bell Palsy



and its cell bodies are located in the spiral ganglion of

the cochlea, which is housed in the modiolus ofthe cochlea (Fig. 18-9 and Tables 18-1 and 18-5).Central processes of the spiral ganglion become thecochlear division of the nerve responsible for thesense of hearing.

Vestibular Nerve

The vestibular nerve cell bodies are located in thevestibular ganglion within the internal auditory mea-tus of the temporal bone. Peripheral processes ofthese neurons divide to enter the vestibular mecha-nism, including the three semicircular canals.

Central processes of these neurons become thevestibular division of the vestibulocochlear nerve re-sponsible for the sense of balance (Fig. 18-9 andTables 18-1 and 18-5).

IX. GLOSSOPHARYNGEAL NERVE

Summary Bite. SVA, GVA, GVE, GSA, and SVE arethe modalities carried in the glossopharyngeal nerve.

The modalities within the glossopharyngeal nerve in-clude: special visceral efferent, general visceral effer-ent, special visceral afferent, general visceral affer-ent, and general somatic afferent (see Fig. 18-10 andTables 18-1, 18-2, and 18-5).

■ Special visceral efferent. Because the glossopha-ryngeal nerve is the nerve of the third pharyngealarch, it serves the only muscle derived from thisarch, the stylopharyngeus muscle.

Conductive hearing loss results from a defect in the con-duction of sound waves from the tympanic membranethrough the bony ossicles to the oval window of thecochlea. Conditions that may contribute to conductiondeafness include buildup of cerumen (ear wax), perfora-tion of the tympanic membrane, otis media (middle earcavity infection), and otosclerosis, excessive growth ofbone around the oval window causing impaired move-ment of the stapes.

Nerve Deafness

Nerve deafness results from a lesion within the nervestransmitting impulses to the brain from the spiral organof Corti. Other causes include certain diseases, drugabuse, and prolonged exposure to loud noises.

Ménière Disease

Ménière disease is related to excess fluid in the en-dolymphatic duct affecting the vestibular mechanism ofthe vestibulocochlear nerve. This disease is character-ized by hearing loss, vertigo, nausea, tinnitus, and

vomiting. Drugs can be used fortreatment, but in severe casessurgery is required.

Otitis Media

The auditory tube permits the spread of infection fromthe nasal cavity into the middle ear cavity. Thiscondition (otitis media), resulting from acute infection,may result in the rupture of the eardrum and/or theinfection may pass into the mastoid air cells. Antibioticsare used to treat this condition. Auditory tube obstruc-tions often lead to middle-ear infections, especially inchildren.

Otosclerosis

Occasionally, the stapes becomes immobilized as a re-sult of bony deposits around the oval window. This con-dition, known as otosclerosis, is a major cause ofhearing loss, especially in older adults. It is usually cor-rectable by surgical procedures. Both otitis media andotosclerosis, if left untreated, will result in deafness.

Conductive Hearing Loss


■ General visceral efferents (parasympathetic) sup-ply the parotid gland and other minor salivaryglands in the mucous membrane in and about theposterior tongue and adjacent pharynx.

■ Special visceral afferents are distributed to thetaste buds located on the posterior one third of thetongue, as well as to those located in the circum-vallate papillae.

■ General visceral afferents supply the posterior onethird of the tongue, the fauces, the palatine tonsils,and the pharynx. Other general visceral sensoryfibers supply the carotid sinus with blood pressurereceptors as well as to chemoreceptors locatedwithin the carotid body. The latter is a sensoryfunction performed in conjunction with the vagusnerve.

■ General somatic afferents supply cutaneous sensa-tion about the ear.

The glossopharyngeal nerve leaves the brain asthree or four rootlets adjacent to the vagus nervealong the medulla between the olive and the inferiorcerebellar peduncle. The rootlets unite to exit theskull through the jugular foramen in company withthe vagus and accessory nerves. Housed in thegroove within the jugular foramen are the superior

and inferior ganglia of the glossopharyngeal nerve,containing the cell bodies of the sensory fibers.

While passing through the jugular foramen, thisnerve communicates with the facial nerve, the auric-ular branch and superior ganglion of the vagus nerve,and the superior cervical sympathetic ganglion.

Tympanic Nerve

The tympanic nerve arises from the inferior ganglionof the glossopharyngeal nerve (Fig. 18-10) and entersthe petrous portion of the temporal bone, traveling tothe tympanic cavity. Here it forms the tympanic

plexus with fibers from the carotid plexus and thegreater petrosal nerve. Branches from the tympanicplexus serve sensory functions to the mucous mem-branes of the eardrum, oval and round windows, mas-toid air cells, and auditory tube.

The tympanic nerve emerges from the tympanicplexus as the lesser petrosal nerve, providing pregan-glionic parasympathetic fibers to the otic ganglion(see Tables 18-1 and 18-2), which it reaches by leav-ing the skull at the fissure between the petrous por-tion of the temporal bone and the greater wing of thesphenoid bone.

The otic ganglion, described in the section on themandibular division of the trigeminal nerve, lies justoutside the foramen ovale, immediately behind themandibular nerve. This ganglion receives pregan-glionic parasympathetic fibers from the lesser petrosal


Figure 18-10. IX. Glossopharyngeal nerve. Observe the communications with the vagus nerve andthe contributions of both to the pharyngeal plexus.


nerve and possibly some fibers from the greater pet-rosal nerve communicated through the tympanicplexus. Postganglionic parasympathetic fibers leavethe otic ganglion and are communicated to the auricu-lotemporal nerve for distribution to the parotid gland,providing it with secretomotor innervation.

Carotid Sinus Nerve

The nerve to the carotid sinus arises as a small fila-ment from the glossopharyngeal nerve subsequent tonerve communications at the jugular foramen. Thisbranch descends along the internal carotid artery,ending in the bifurcation of the common carotid ar-tery (Fig. 18-10). This nerve functions as a barorecep-tor within the carotid sinus. On its way to the carotidsinus, the nerve communicates with pharyngealbranch(es) of the vagus and branches from the supe-rior cervical ganglion (postganglionic sympatheticfibers). Glossopharyngeal and vagus nerves transmitafferent fibers from the chemoreceptors within thecarotid body.

Nerve to the Stylopharyngeus Muscle

As the glossopharyngeal nerve courses to the poste-rior pharyngeal wall, a nerve to the stylopharyngeusmuscle arises to supply that muscle (Fig. 18-10).

Pharyngeal Branches

The main trunk of the glossopharyngeal nerve termi-nates as several pharyngeal branches to enter the pos-terior pharyngeal wall (Fig. 18-10). Some of thesebranches continue to the tongue as lingual branches,providing general sensation to the posterior one thirdof the tongue and special sensory fibers to the tastebuds on that portion of the tongue as well as to those ofthe circumvallate papillae. Other branches penetratethe pharyngeal wall as tonsillar branches, communi-cating with the lesser palatine nerve of the maxillary

division of the trigeminal nerve, to supply the softpalate, pharynx, and fauces with general sensation.

Pharyngeal Plexus

Other fibers of the glossopharyngeal nerve join withpharyngeal branches of the vagus nerve and branchesfrom the superior cervical ganglion to form the pha-

ryngeal plexus, located on the wall of the middle pha-ryngeal constrictor muscle (Fig 18-10). Branches fromthis plexus penetrate the wall of the pharynx and sup-ply all of the muscles of the pharynx (except the sty-lopharyngeus) and soft palate (except the tensor velipalatini) with motor innervation and adjacent mu-cous membranes with sensory innervation.

Although the following information was pre-sented in Chapter 16, it is appropriate to present itagain because there is confusion related to the func-tion of the individual nerves making up the pharyn-geal plexus. Glossopharyngeal contributions to thepharyngeal plexus are sensory, whereas the vagalbranches are motor. However, these motor branchesare believed to consist mainly of fibers from the cra-nial portion of the accessory nerve (cranial nerve XI),which are contributed to the vagus nerve before itexits the skull. Postganglionic sympathetic fibers con-tributed from the superior cervical ganglion to thepharyngeal plexus are vasomotor in function.

X. VAGUS NERVE

Summary Bite. GVE, SVE, GVA, and GSA are themodalities carried in the vagus nerve.

The cranial nerve having the most extensive distribu-tion is the vagus nerve. In addition to its destinationswithin the head and neck, the vagus nerve also entersthe thorax to serve the heart and lungs, and continues

Unilateral lesion of the glossopharyngeal nerve outside

of the brainstem will cause loss of taste from the poste-rior one third of the tongue, loss of salivation from the

parotid gland on the ipsilateralside, loss of gag reflex, and lossof carotid sinus reflex.

Unilateral Lesion of the Glossopharyngeal NerveOutside Brainstem


into the abdomen to supply most of the abdominal vis-cera (Figs. 18-10 and 18-11 and Tables 18-1 and 18-5).

The vagus nerve possesses five modalities,namely, special visceral efferent general somatic af-ferent, general visceral afferent, special visceral affer-ent, general visceral efferent.

■ Special visceral efferent. The vagus is the nerve ofthe fourth pharyngeal arch, and its recurrent la-ryngeal branch is the nerve of the sixth pharyngealarch. Consequently, the vagus nerve supplies mus-cles developed from those arches. Muscles devel-oping from the fourth arch include the pharyngealconstrictors and the cricothyroid muscles. Musclesdeveloped from the sixth arch include the intrinsicmuscles of the larynx.

■ General somatic afferent fibers are provided to theskin about the ear and external acoustic meatus.

■ General visceral afferent supplies the mucous mem-branes of the pharynx, larynx, esophagus, bronchi,lungs, heart, and much of the abdominal viscera.

■ General visceral efferent supplies the smooth mus-cles and glands of the digestive tract from theesophagus to (and including) most of the intes-tines, plus the bronchi and trachea.

■ Special visceral afferent is supplied to the base ofthe tongue, aryepiglottic fold, and larynx.

The vagus nerve exits the brain at the medulla,between the olive and the inferior cerebellar pedun-cle just posterior to the glossopharyngeal nerve, via acluster of 8 to 10 rootlets that unite to exit the skull


Figure 18-11. X. Vagus nerve. Only those branches arising in the head and neck are illustrated.


through the jugular foramen along with the glos-sopharyngeal and accessory nerves.

This nerve possesses two sensory ganglia: the su-

perior ganglion, housed in the jugular fossa, and theinferior (nodose) ganglion, appearing as a swelling onthe nerve just after it exits the jugular foramen (Figs.18-10 and 18-11).

Peripheral processes of the neurons in these gan-glia are distributed with the vagus nerve as the sen-sory component. These ganglia receive communica-tions from the glossopharyngeal, facial, accessory,and hypoglossal nerves. The sympathetic nervoussystem communicates via a filament from the supe-rior cervical ganglion, and a communication also ex-ists between the vagal ganglia and the first andsecond cervical nerves.

The cranial root of the accessory nerve joins thevagus nerve just proximal to the inferior ganglion.Thus, the motor component to the muscles arisingfrom the fourth and fifth pharyngeal arches, gener-ally described as arising from the vagus nerve, are ac-tually from this contribution to the vagus nerve bythe accessory nerve. However, autonomic motor in-nervation to the esophagus and the structures withinthe thorax and abdomen attributed to the vagus arisefrom the dorsal motor nucleus of the vagus nerve.

Before its exit from the jugular fossa the vagusnerve gives off two branches: the meningeal and au-ricular branches.

Meningeal Branch

The meningeal branch of the vagus nerve returns tothe cranial vault to supply the dura in the posteriorcranial fossa (Fig. 18-11).

Auricular Branch

An auricular branch arises from the superior vagalganglion, communicates with the glossopharyngealnerve, and then enters the mastoid canal coursing tothe facial canal. Here it communicates with the facialnerve, then exits through the tympanomastoid sutureto communicate with the posterior auricular nervebefore distributing to the skin of the posterior aspectof the ear and the external acoustic meatus.

Vagal Branches in the Neck

The following sections describe the branches and dis-tributions of the vagus nerve as it courses through theneck. Branches arising from the vagus in the neckinclude the pharyngeal, superior laryngeal, and supe-rior cardiac nerves. Also located in the neck is the

recurrent laryngeal nerve that arises from the vagusnerve at the thoracic inlet to recur back into the neck.

Pharyngeal Branches

Pharyngeal branches of the vagus arise from the infe-rior vagal ganglion and pass over the internal carotidartery to the pharyngeal constrictor muscles, provid-ing input to the pharyngeal plexus (Fig. 18-11). Fromthis plexus, motor innervation is supplied to the pha-ryngeal but not the stylopharyngeus, as well as to allmuscles of the soft palate except the tensor veli pala-tini. Mucous membranes of the pharynx are also sup-plied by the pharyngeal plexus.

Usually, the nerve to the carotid body originatesfrom the pharyngeal branches. This nerve descendsalong the internal carotid artery to terminate in thecarotid body housed in the bifurcation of the commoncarotid artery (Fig. 18-11). Chemoreceptors detectchanges in oxygen and carbon dioxide tension as wellas hydrogen ion concentration in the blood at this site.

As previously described, sensory fibers from thecarotid body are also transmitted in the glossopharyn-geal nerve.

Superior Laryngeal Nerve

The superior laryngeal nerve arises from the vagus atthe inferior end of the inferior ganglion and passesdeep to the internal carotid artery, descending to thethyroid cartilage, where it divides into external andinternal branches (Fig. 18-11).

The smaller external branch continues to de-scend beneath the sternothyroid muscle to enter thecricothyroid and inferior pharyngeal constrictor mus-cles, which it supplies with motor innervation.

The larger internal branch courses over andpierces the thyrohyoid membrane. This branch sup-plies sensory innervation to the mucous membranessuperiorly, to the base of the tongue, and to theepiglottis and the larynx as far inferiorly as the vocalfolds. It is with this branch that the sensation of tasteis transmitted to the brain from the base of thetongue, epiglottis, and larynx.

The internal laryngeal branch also containsparasympathetic fibers to the glands associated withthe mucous membranes of the regions just described.Preganglionic fibers synapse on ganglionic plexuseswithin the walls of the viscera served, and from therethe postganglionic fibers distribute secretomotorfibers to the glands.

Superior Cardiac Branches

As the trunk of the vagus nerve descends in the neckwithin the carotid sheath, between and posterior to theinternal jugular vein and the internal carotid artery,superior cardiac branches are given off and descend

into the thorax (Fig. 18-11). Their function is not de-scribed here because it is outside the realm of this text.

Recurrent Laryngeal Nerve

At the root of the neck, the recurrent laryngeal nervearises from the vagus and ascends back into the neck.On the right side, the nerve recurs around the subcla-vian artery, whereas on the left side the nerve recursaround the arch of the aorta (Fig. 18-11).

Upon reentering the neck, each recurrent laryn-geal nerve follows a similar course deep to the carotidartery, along a groove between the trachea and theesophagus, to enter the larynx as inferior laryngeal

nerves, piercing the cricothyroid membrane to sup-ply all of the intrinsic muscles of the larynx, exceptthe cricothyroid muscle, with motor innervation.

In the recurrent laryngeal nerve’s path to thelarynx, branches to the trachea and the esophagussupply those structures with sensory and parasympa-thetic innervation in much the same manner as thefibers of the internal branch of the superior laryngealnerve but more distally. In addition, pharyngeal

branches are supplied to the inferior pharyngeal con-strictor muscle. Although they serve a minor role,sensory branches of the inferior laryngeal nerve pro-vide sensory fibers to the larynx and overlap sensoryfibers of the external laryngeal nerve.

The remaining branches and distributions of thevagus nerve within the thorax and abdomen are notdescribed here. Those interested in this subject are re-ferred to general textbooks in gross anatomy and neu-roanatomy, as suggested in the Selected Readings.

XI. ACCESSORY NERVE

Summary Bite. SVE (communicated to the vagusnerve for the muscles of the pharynx and larynx) and

SVE (assuming branchomeric origins for the sternocleido-mastoid and trapezius muscles) are the modalities carriedby the accessory nerve.

The accessory nerve arises from two sources: thebrain and the spinal cord. This nerve is described asa motor nerve, serving the sternocleidomastoid andtrapezius muscles, and its cranial root is regarded asthe motor portion of the vagus nerve within the headand neck, including the contribution that the vagusnerve makes to the pharyngeal plexus.

The spinal portion arises from motor neurons inthe first five (or more) spinal cord segments. Thisportion of the nerve emerges on the surface of the


Pharynx

Such a lesion results in flaccid paralysis or weakness inthe muscles of the pharynx that bring about dysphagia(difficulty in swallowing); paralysis or weakness of themuscles of the larynx, resulting in dysphonia (hoarse-ness); paralysis or weakness in the soft palate; loss ofsensation from pharynx and larynx, and the loss of thegag reflex. Bilateral lesion of the vagus nerve is notcompatible with life.

Larynx

The intrinsic laryngeal musculature is served by twobranches of the vagus nerve, the inferior laryngealbranch of the recurrent laryngeal nerve and the externalbranch of the superior laryngeal nerve. Because thesetwo nerves are prone to damage, it is essential that they

be protected from injury duringsurgical procedures. The externallaryngeal nerve, passing deep to the superior thyroid ar-tery, supplies only a single muscle, the cricothyroid. Itssection does not cause excessive damage to phonation.It will, however, affect the ability to tense the vocal cordsand the ability of the patient to produce high-pitchedsounds. In addition, damage to it causes some hoarse-ness and easy tiring of the voice.

Damage to the recurrent laryngeal or the inferiorlaryngeal nerves will result in serious complications,whose severity depends on the degree of damageand whether the injury is bilateral. Involvement mayrange from slight hoarseness to complete inability tovocalize and breathe, necessitating performance of atracheotomy.

Unilateral Lesion of the Vagus after LeavingBrainstem



spinal cord to ascend into the skull via the foramenmagnum to join or communicate with the cranialportion of the nerve before exiting the jugular fora-men along with the vagus and glossopharyngealnerves (Figs. 18-10 and 18-12 and Tables 18-1 and 18-5). The cranial portion leaves the brain very closeto the vagus nerve and travels along with it to thejugular foramen. After communicating with thespinal portion, the cranial portion joins the vagus,and the spinal portion continues on to descendthrough the foramen.

The spinal portion descends posterior to the sty-lohyoid and digastric muscles to enter the sternoclei-

domastoid muscle, which it pierces and serves beforepassing obliquely over the posterior triangle to termi-nate in and supply the trapezius muscle. Along itsway, the nerve communicates with the second, third,and fourth cervical nerves.

XII. HYPOGLOSSAL NERVE

Summary Bite. GSE is the modality carried by thehypoglossal nerve.

The accessory nerve, as it progresses subcutaneouslythrough the neck, is subject to injury, (e.g., during lymphnode biopsy, carotid artery and/or internal jugular veinsurgical procedures). Injury produces weakness in the

sternocleidomastoid and trapez-ius muscles, impairing neckmovement and resulting in adrooping of the shoulder.

Accessory Nerve Injury


Figure 18-12. XI. Accessory nerve. Note the spinal portion ascending into thecranium to join the cranial portion before exiting the jugular foramen.

The most caudal and the last of the cranial nerves isthe hypoglossal nerve. This nerve is the motor nerveof the tongue.

It arises as several rootlets from the medulla be-tween the olive and the pyramid and, passing throughthe hypoglossal canal, the rootlets unite to form a sin-gle nerve. It descends deep to the internal jugular veinand internal carotid artery, and then becomes superfi-cial to them as it crosses them at the mandible.

The hypoglossal nerve then courses over the ex-ternal carotid and lingual arteries deep to the digas-tric and stylohyoid muscles. It enters the muscles ofthe tongue, which it supplies, proceeding to the ven-tral tip of the tongue.

With the exception of the palatoglossus (inner-vated by the vagus via the pharyngeal plexus), the hy-

poglossal nerve innervates the hyoglossus, styloglos-sus, genioglossus, and intrinsic muscles of the tongue(Fig. 18-13 and Tables 18-1 and 18-5).

The hypoglossal nerve communicates with sev-eral nerves in its route, including the pharyngealplexus, the lingual, and the first and second cervicalspinal nerves. Branches from the first and secondventral cervical spinal nerves join the hypoglossallater to exit, forming the descending loop (superiorroot) of the ansa cervicalis, which innervates the in-frahyoid muscles.

Some of the fibers from the first cervical nervecontinue on to exit from the hypoglossal nerve nearthe posterior border of the hyoglossus muscle andenter the thyrohyoid and geniohyoid muscles, sup-plying them with motor innervation.


Figure 18-13. XII. Hypoglossal nerve.

Difficult third molar extractions and/or fractures of themandible may damage the hypoglossal nerve (cranialnerve XII), causing paralysis of the tongue on the af-fected side. When the mouth is opened and the tongueis protruded, the genioglossus of the unaffected side will

cause the tongue to deviate tothe affected side. If the damageis prolonged, the tongue mus-cles will atrophy.

Hypoglossal Nerve Injury


TEXTBOOK OF HEAD & NECK ANATOMY, Fourth Edition · 2020-01-22 · books of neuroanatomy. Each of...

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