Cranial Nerves - Wiley-Blackwell

1 A 70-year-old male has excruci-ating pain in the lower left part ofhis face. This began 1 month ago. Hedescribes it as being like a jolt of lightningthat radiates from his left ear, down to hisjaw, and to the side of his mouth. Thesejolts of pain occur numerous times eachday. Between attacks his face seems normal. He denies any numbness or tingling sensations. There is no hearingabnormality. The pain is triggered bytalking, chewing, or touch of the lowerleft part of his face. He is unable to eat orbrush his teeth, particularly on the leftside, since he fears triggering anotherpainful attack. He can only drink hismeals through a straw and cannot lie inbed on his left side. He had the samesymptoms about 2 years ago. At that timehe was treated with a medication whichhelped; symptoms subsided, but hestopped taking the medicine. The pain isso distressing that the patient admits tocontemplating general and neurologic exam isnormal, except that he withdraws andwill not let anyone touch the left side ofhis CASET here are 12 pairs of Cranial Nerves emerging from the brainand radiating from its surface (Fig.)

2 They pass throughskull foramina, fissures, or canals to exit the Cranial vault andthen distribute their innervation to their respective structuresin the head and neck. One of the Cranial Nerves , the vagus (L., wanderer ) continues into the trunk where it innervatesvarious thoracic and abdominal addition to being named, the Cranial Nerves are num-bered sequentially with Roman numerals in the order inwhich they arise from the brain, rostrally to caudally. The CHAPTER 15 Cranial NervesCLINICAL CASEOLFACTORY NERVE (CN I)OPTIC NERVE (CN II)OCULOMOTOR NERVE (CN III)TROCHLEAR NERVE (CN IV)TRIGEMINAL NERVE (CN V)ABDUCENT NERVE (CN VI)FACIAL NERVE (CN VII)VESTIBULOCOCHLEAR NERVE (CN VIII)GLOSSOPHARYNGEAL NERVE (CN IX)VAGUS NERVE (CN X)SPINAL ACCESSORY NERVE (CN XI)HYPOGLOSSAL NERVE (CN XII)SYNONYMS AND EPONYMSFOLLOW-UP TO CLINICAL CASEQUESTIONS TO PONDERATOC15 3/17/06 10.

3 20 AM Page 253following list includes their names and corresponding Vestibulocochlear accessory the Cranial Nerves and their sensory andparasympathetic ganglia (Tables , ) form part of theperipheral nervous system, the optic nerve is really an out-growth of the brain that emerges from the prosencephalon(not the brainstem as other Cranial Nerves ), and is thereforenot a typical Cranial nerve. Moreover, part of the spinal accessory nerve arises from the cervical spinal cord; thusthere are only nine pairs of Cranial Nerves that emerge fromthe main sensory and motor nuclei of the Cranial nervesare shown in Fig. describing the various functional components (modal-ities) of the Cranial Nerves , the definition of the followingterms should be kept in mind: afferentis sensory input.

4 Efferentis motor output that may be somaticto skeletal muscles or visceralto smooth muscle, cardiac muscle, and glands, and254===CHAPTER 15 Figure view of the brainstem showing the Cranial nerve associationTrigeminal (semilunar, Gasserian)Trigeminal (V)GeniculateFacial (VII)Cochlear (spiral)Cochlear (VIII)Vestibular (Scarpa s)Vestibular (VIII)Superior glossopharyngealGlossopharyngeal (IX)Inferior glossopharyngealGlossopharyngeal (IX)Superior vagalVagus (X)Inferior vagal (nodose)Vagus (X)Table ganglia of the Cranial nervesATOC15 3/17/06 10:20 AM Page 254 Cranial Nerves ===255special visceral efferent to striated muscles derived from the branchial arches; generalrefers to those components thatmay be carried by Cranial Nerves as well as spinal Nerves ; special refers to functional components that are carried by Cranial Nerves only.

5 The following categories describe thefunctional components carried by the various Cranial Nerves (Table ).1 General somatic afferent(GSA). These fibers carry gen-eral sensation (touch, pressure, pain, and temperature)from cutaneous structures and mucous membranes of thehead, and general proprioception(GP) from somaticstructures such as muscles, tendons, and joints of the headand neck. The trigeminal, facial, glossopharyngeal, andvagus Nerves transmit GSA input to the spinal nucleus ofthe trigeminal somatic efferent(GSE). These fibers providegeneral motor innervation to skeletal muscles derivedfrom embryonic somites. The oculomotor, trochlear, andabducent Nerves innervate the extraocular muscles thatMesencephalic tractand nucleus of CN VEdinger Westphal nucleusOculomotor nucleusTrochlear nucleusMotor nucleus of CN VAbducens nucleusSuperior salivatory nucleusFacial nucleusInferior salivatory nucleusHypoglossal nucleusDorsal motor nucleus of CN XNucleus ambiguusSpinal accessory nucleusMain sensory nucleus of CN VSpinal nucleus of CN VNucleus of the solitary tractFigure nuclei of the Cranial Nerves .

6 Thesensory nuclei are illustrated on the left, and the motor nucleion the nerveassociationassociationTrigeminalFun ction(s)CiliaryOculomotor (III)Ophthalmic divisionConstricts pupil;lens accommodationPterygopalatineFacial (VII)Maxillary divisionLacrimation; nasal gland,and minor salivary gland secretionSubmandibularFacial (VII)Mandibular divisionSalivation (parotid gland)OticGlossopharyngeal (IX)Mandibular divisionSalivation (submandibular and sublingual glands)IntramuralVagus (X)Gland secretion;peristalsisTable ganglia ofthe Cranial 3/17/06 10:20 AM Page 255control eye movements, whereas the hypoglossal nervesupplies motor innervation to the muscles of the tongue,mediating movement of the visceral afferent(GVA). General sensation fromthe viscera is transmitted by the facial, glossopharyngeal,and vagus visceral efferent(GVE). These fibers provide vis-ceral motor (parasympathetic) innervation to the only Cranial Nerves that transmit parasympatheticfibers are the oculomotor, facial, glossopharyngeal, andvagus somatic afferent(SSA).

7 These fibers carry specialsensory input from the eye (retina), for vision, and fromthe ear (vestibular apparatus for equilibrium, and cochleafor hearing). The only Nerves transmitting this componentare the optic and vestibulocochlear visceral afferent(SVA). These are special sensoryfibers from the viscera. These fibers convey the specialsense of smell transmitted by the olfactory nerve and thespecial sense of taste transmitted by the facial, glosso-pharyngeal, and vagus visceral efferent(SVE). These motor fibers arespecial because they supply motor innervation to skeletalmuscles of branchial arch origin. These fibers are carriedby the Nerves of the branchial arches, which are thetrigeminal, facial, glossopharyngeal, and vagus summarizes the modalities, nuclei, ganglia, andfunctions of the Cranial NERVE (CN I)The bipolar olfactory re-ceptor cells(first order sensory neurons) of theolfactory apparatus residenot in a sensory ganglion,but instead in the olfactory epithelium (neuroepithelium)ofthe modified nasal mucosa lining the roof and adjacent upperwalls of the nasal cavities (see Fig.)

8 The axons of thesebipolar neurons are SVA fiberstransmitting olfactorysensa-tion. These axons assemble to form bundles, the olfactory fila(L., threads ), which collectively form Cranial nerve I. Theolfactory fila traverse the fenestrations of the cribriform plateof the ethmoid bone to terminate in the olfactory bulb wherethey synapse with second order relay neuronsand inter-neurons(see Chapter 19).OPTIC NERVE (CN II)The optic nervemediates thespecial sense of visionvia itsSSA fibers. Light enteringthe eye activates cells knownas rods and cones, the photoreceptors of the retina. Electricalsignals generated by the photoreceptors are transmitted toother cells of the retina that process and integrate sensoryinput. The first order sensory bipolar neuronsof the visualpathway reside in the retina and transmit electrical signals of visual sensory input to the multipolar second order ganglion cellsof the retina.

9 The ganglion cells give rise tounmyelinated axons that converge at the optic disc and traverse the lamina cribrosa, a sieve-like perforated area ofthe sclera, to emerge from the back of the eyebulb. At thispoint, the ganglion cell axons acquire a myelin sheath andassemble to form the optic nerve. This nerve, an outgrowth ofthe diencephalon, leaves the orbit via the optic canal to enterthe middle Cranial fossa. There, the optic Nerves of the rightand left sides join each other to form the optic chiasma(G., optic crossing ) where partial decussation of the optic nervefibers of the two sides takes place. All ganglion cell axonsarising from the nasal halfof the retina decussate(through thecentral region of the chiasma) to the opposite optic tract. Allganglion cell axons arising from the temporal halfof the256===CHAPTER 15 ModalityGeneral somatic afferent (GSA)General somatic efferent (GSE)General visceral afferent (GVA)General visceral efferent (GVE)Special somatic afferent (SSA)Special visceral afferent (SVA)Special visceral efferent (SVE)Function(s)General sensation andgeneral proprioceptionMotor supply to extraocular musclesMotor supply to tongueGeneral sensation from visceraParasympathetic fibers to visceraSpecial sensory input from retinaSpecial sensory input fromvestibulocochlear apparatusSpecial sense of smellSpecial sense of tasteMotor innervation to muscles ofbranchiomeric origin.

10 Mandibular, hyoid,3rd, 4th, and 6th branchial archesCranial nervesV, VII, IX, XIII, IV, VIXIIVII, IX, XIII, VII, IX, XIIVIIIIVII, IX, XV, VII, IX, XTable nerve olfactory receptor cells reside in theolfactory epithelium, and not in asensory ganglion as is typical of othercranial nervesThe optic nerve consists of themyelinated axons of the retinalganglion cellsATOC15 3/17/06 10:20 AM Page 256 Cranial nerveI OlfactoryII OpticIII OculomotorIV TrochlearV TrigeminalVI AbducentVII FacialTable receptors. Functionalcomponent(modality)SVASSAGSEGV E (parasympathetic)GPGSEGPSVEGSAGPGSEGPSVE GVE (parasympathetic)SVAGVAN ucleus OculomotorEdinger WestphalMesencephalicnucleus of thetrigeminalTrochlearMesencephalicnucle us of thetrigeminalMotor nucleus ofthe trigeminalMain (chief,principal)nucleus of thetrigeminalSpinal nucleus ofthe trigeminalMesencephalicnucleus of thetrigeminalAbducensMesencephalicnucleu s of thetrigeminalFacialSuperior salivatorySolitariusSolitariusLocation of Cranial nerve nucleiTelencephalonDiencephalonMesenceph alon(tegmentum)Mesencephalon(tegmentum)M esencephalonMesencephalon(tegmentum)Mese ncephalonMetencephalonMetencephalon(pons )Metencephalon(pons to C3)MesencephalonMetencephalon(pons)Mesen cephalonMetencephalon(pons)Myelencephalo nMyelencephalonMyelencephalonGanglion Ciliary(parasympathetic)