THE PTERYGOPALATINE FOSSA MAXILLARY NERVE EAR VESTIBULOCOCHLEAR NERVE CN VIII

Transcription

1 THE PTERYGOPALATINE FOSSA MAXILLARY NERVE EAR VESTIBULOCOCHLEAR NERVE CN VIII 1

2 THE PTERYGOPALATINE FOSSA 2

3 THE PTERYGOPALATINE FOSSA The pterygopala/ne fossa lies between: the pterygoid process of the sphenoid posteriorly and the rounded posterior aspect of the maxilla anteriorly. THE PTERYGOPALATINE FOSSA The pterygopala/ne fossa is an irregularly shaped space posterior to the maxilla and inferior and deep to the zygoma/c arch. Because of its strategic loca/on, the pterygopala/ne fossa is a major site of distribu/on for the maxillary nerve V 2 and for the terminal part of the maxillary artery. 3

4 THE PTERYGOPALATINE FOSSA BOUNDARIES OF THE PTERYGOPALATINE FOSSA: Anterior: Posterior surface of maxilla THE PTERYGOPALATINE FOSSA Posterior: Lateral plate of pterygoid process and greater wing of sphenoid Superior: the body of the sphenoid, infratemporal surface of the greater wing of the sphenoid and orbital surface of the pala/ne bone Inferior: Pyramidal process of the palalne bone Medial: Perpendicular plate of palalne bone Lateral: Open through pterygomaxillary fissure 4

5 THE PTERYGOPALATINE FOSSA Anteriorly, the pterygopala/ne fossa is closely related to the orbit through the inferior orbital fissure Medially, it is related to the nasal cavity through the sphenopalalne foramen Inferiorly, it is related to the oral region through the greater and lesser palalne foramina Laterally, it is related to the infratemporal fossa through the pterygomaxillary fissure THE PTERYGOPALATINE FOSSA Posterosuperiorly, it is related to the middle cranial fossa through the foramen rotundum and pterygoid canal. 5

6 THE PTERYGOPALATINE FOSSA 6

7 THE PTERYGOPALATINE FOSSA THE PTERYGOPALATINE FOSSA - OPENNINGS PTERYGOMAXILLARY FISSURE SPHENOPALATINE FORAMEN INFERIOR ORBITAL FISSURE THE INFRATEMPORAL FOSSA THE NASAL CAVITY THE ORBIT PALATINE CANAL THE HARD AND THE SOFT PALATE FORAMEN ROTUNDUM THE MIDDLE CRANIAL FOSSA PTERYGOID CANAL PHARYNGEAL CANAL THE FORAMEN LACERUM THE NASOPHARYNX 7

8 THE PTERYGOPALATINE FOSSA THE PTERYGOPALATINE FOSSA The pterygopalalne fossa contains: the maxillary nerve V 2 the pterygopalalne ganglion the nerve of the pterygoid canal, and the third or pterygopalalne part of the maxillary artery and its branches 8

9 THE PTERYGOPALATINE FOSSA THE PTERYGOPALATINE FOSSA LymphaLc drainage of the temporal, infratemporal, and pterygopala/ne fossae is to regional lymph nodes - the superficial nodes at the junc/on of the head and neck and the superior deep cervical nodes along the caro/d sheath. 9

10 THE MAXILLARY NERVE THE MAXILLARY NERVE The main nerves associated with the temporal, infratemporal, and pterygopala/ne fossae are branches of the maxillary V 2 and mandibular V 3 nerves, which are divisions of the trigeminal nerve CN V The maxillary nerve V 2 leaves the middle cranial fossa through the foramen rotundum and enters the pterygopalalne fossa. It is a sensory nerve with no motor component, and its branches provide sensa/on to the midsec/on of the face: lower part of the orbit, nose, upper part of the mouth, and cheek 10

11 THE MAXILLARY NERVE THE MAXILLARY NERVE A^er entering the pterygopala/ne fossa, the maxillary nerve V 2 gives rise to: the zygomalc nerve, two pterygopalalne nerves, and the posterior superior alveolar nerves (which supply the maxillary sinus and maxillary molars). The zygomalc nerve further divides into: the zygomalcofacial and the zygomalcotemporal nerves, which provide sensa/on to the respec/ve regions of the upper lateral aspect of the face The pterygopalalne nerves suspend the pterygopalalne ganglion within the pterygopala/ne fossa. The posterior superior alveolar nerves supplies the maxillary sinus and maxillary molars. 11

12 THE MAXILLARY NERVE THE MAXILLARY NERVE This ganglion receives autonomic innerva/on from the nerve of the pterygoid canal, which is a combina/on of two nerves: the parasympathelc root (a branch of the facial nerve [VII]) the sympathelc root (which originates from the superior cervical ganglion) Nerves from the pterygopalalne ganglion carry parasympathe/c and sympathe/c fibers and sensory nerves from the maxillary nerve V 2 to supply: the lacrimal gland and glands in the nasal and upper oropharyngeal regions. 12

13 THE MAXILLARY NERVE THE MAXILLARY NERVE The maxillary nerve V 2 leaves the pterygopala/ne fossa through the inferior orbital fissure. From this point it is referred to as the infra-orbital nerve It enters the orbit and passes anteriorly within the infra-orbital groove and then within the infra-orbital canal un/l it emerges onto the face approximately 1 cm inferior to the inferior orbital rim The infra-orbital nerve provides sensa/on to: the skin of the upper lip, lower eyelid, cheek, and lateral part of the nose. 13

14 THE PTERYGOPALATINE GANGLION THE PTERYGOPALATINE GANGLION Is the largest of the four parasympathe/c ganglia in the head and is formed by the cell bodies of the postganglionic neurons associated with preganglionic parasympathe/c fibers of the facial nerve [VII] carried by the greater petrosal nerve and the nerve of the pterygoid canal. The maxillary nerve gives off the two ganglionic branches to the pterygopala/ne ganglion (sensory roots of the pterygopala/ne ganglion) that suspend the parasympathe/c pterygopala/ne ganglion in the superior part of the pterygopala/ne fossa 14

15 THE PTERYGOPALATINE GANGLION THE PTERYGOPALATINE GANGLION 3 sets of nerve fibers travel through the pterygopala/ne ganglion: General sensory fibers from the maxillary n. (without synapsing!) The pterygopala/ne nerves convey general sensory fibers of the maxillary nerve, which pass through the pterygopala/ne ganglion without synapsing to supply the nose, palate, and pharynx The deep petrosal nerve is a sympathelc nerve arising from the internal caro/d plexus as the artery exits the caro/d canal. It conveys postsynap/c fibers from nerve cell bodies in the superior cervical sympathe/c ganglion to the pterygopala/ne ganglion by joining the nerve to the pterygoid canal Preganglionic parasympathelc fibers carried to the pterygopala/ne ganglion via the vidian n. and formed by synapsing in the pterygopala/ne ganglion with the postganglionic parasympathe/c fibers The parasympathe/c fibers to the pterygopala/ne ganglion come from the facial nerve VII by way of its first branch, the greater petrosal nerve 15

16 THE PTERYGOPALATINE GANGLION THE PTERYGOPALATINE GANGLION All branches arising from the pterygopala/ne ganglion carry these 3 sets of fibers to the areas where they terminate. These nerves of the maxillary division travel through the pterygopala/ne ganglion: nasopala/ne n. posterior superior nasal n. greater pala/ne n. lesser pala/ne n. pharyngeal n. This ganglion receives autonomic innerva/on from the nerve of the pterygoid canal, which is a combina/on of two nerves: the parasympathelc root - a branch of the facial nerve CN VII the sympathelc root - originates from the superior cervical ganglion 16

17 THE PTERYGOPALATINE GANGLION THE PTERYGOPALATINE GANGLION The majority of the branches of the ganglion are primarily sensory branches of the maxillary nerve. Thus they pass through the ganglion without synapsing and enter the maxillary nerve through its ganglionic branches; they convey some parasympathe/c fibres to the pala/ne, pharyngeal and nasal mucous glands. General sensory fibres des/ned for distribu/on via orbital, nasopala/ne, superior alveolar, pala/ne and pharyngeal branches of the maxillary division of the trigeminal nerve run through the ganglion without synapsing. 17

18 THE PTERYGOPALATINE GANGLION THE PTERYGOPALATINE GANGLION Preganglionic parasympathe/c fibres des/ned for the pterygopala/ne ganglion run ini/ally in the greater petrosal branch of the facial nerve, and then in the nerve of the pterygoid canal (Vidian nerve), a^er the greater petrosal unites with the deep petrosal nerve. Postganglionic parasympathe/c fibres leave the ganglion; some may join the maxillary nerve via a ganglionic branch and then travel via the zygoma/c and zygoma/cotemporal branches of the maxillary nerve to the lacrimal gland, but most are thought to travel by orbital branches to the gland Postganglionic sympathe/c fibres pass through the ganglion without synapsing and supply blood vessels and orbitalis. 18

19 THE EXTERNAL EAR The auricle is supported by car/lage and is covered by skin. The external auditory meatus is near the anterior margin of the auricle. The auriculotemporal nerve, a branch of CN V3, supplies the skin of the auricle anterior to the external acous/c meatus THE EAR Minor contribu/ons of embryological significance are made to the skin of the concha and its eminence by: the vagus CN X and the facial nerves CN VII. 19

20 THE EXTERNAL EAR THE EAR The lympha/c drainage of the auricle is as follows: the lateral surface of the superior half of the auricle drains to the superficial paro/d lymph nodes the cranial surface of the superior half of the auricle drains to the mastoid lymph nodes and deep cervical lymph nodes; the remainder of the auricle, including the lobule, drains into the superficial cervical lymph nodes. 20

21 THE EXTERNAL EAR THE EAR THE TYMPANIC MEMBRANE The tympanic membrane, approximately 1 cm in diameter, is a thin, oval semitransparent membrane at the medial end of the external acous/c meatus. The tympanic membrane forms a par//on between the meatus of the external ear and the tympanic cavity of the middle ear. Viewed through an otoscope, the tympanic membrane has a concavity toward the external acous/c meatus with a shallow, cone-like central depression, the peak of which is the umbo. Superior to the lateral process of the malleus (one of the small ear bones, or auditory ossicles, of the middle ear), the membrane is thin and is called the flaccid part. It lacks the radial and circular fibers present in the remainder of the membrane, called the tense part. 21

22 THE EXTERNAL EAR THE TYMPANIC MEMBRANE The external surface of the tympanic membrane is supplied mainly by the auriculotemporal nerve, a branch of CN V3 Some innerva/on is supplied by a small auricular branch of the vagus (CN X). The internal surface of the tympanic membrane is supplied by the glossopharyngeal nerve (CN IX). THE EAR 22

23 THE MIDDLE EAR The contents of the middle ear are the: auditory ossicles (malleus, incus, and stapes) stapedius and tensor tympani muscles chorda tympani nerve, a branch of CN VII tympanic plexus of nerves THE MIDDLE EAR 23

24 THE 6 WALLS THE TYMPANIC CAVITY THE MIDDLE EAR 1. The tegmental wall (roof) is formed by a thin plate of bone, the tegmen tympani, which separates the tympanic cavity from the dura mater on the floor of the middle cranial fossa. 2. The jugular wall (floor) is formed by a layer of bone that separates the tympanic cavity from the superior bulb of the internal jugular vein. 3. The membranous wall (lateral wall) is formed almost en/rely by the peaked convexity of the tympanic membrane; superiorly it is formed by the lateral bony wall of the epitympanic recess. The handle of the malleus is akached to the tympanic membrane, and its head extends into the epitympanic recess. 24

25 THE 6 WALLS THE TYMPANIC CAVITY THE MIDDLE EAR 4. The labyrinthine wall (medial wall) separates the tympanic cavity from the internal ear. It also features the promontory of the labyrinthine wall, formed by the ini/al part (basal turn) of the cochlea, and the oval and round windows, which, in a dry cranium, communicate with the internal ear. 5. The mastoid wall (posterior wall) features an opening in its superior part, the aditus to the mastoid antrum, connec/ng the tympanic cavity to the mastoid cells; the canal for the facial nerve descends between the posterior wall and the antrum, medial to the aditus. 6. The anterior carold wall separates the tympanic cavity from the caro/d canal; superiorly, it has the opening of the pharyngotympanic tube and the canal for the tensor tympani. 25

26 THE TYMPANIC CAVITY THE MIDDLE EAR RELATIONSHIPS 1. The tegmental wall (roof) - middle cranial fossa and temporal lobe 2. The jugular wall (floor) - bulb of internal jugular vein 3. The membranous wall (lateral wall) - tympanic membrane and epitympanic recess 4. The labyrinthine wall (medial wall) - inner ear, facial nerve [VII] 5. The mastoid wall (posterior wall) - mastoid antrum, facial nerve [VII] 6. The anterior carold wall - pharyngotympanic tube and internal caro/d artery 26

27 THE TYMPANIC CAVITY THE MIDDLE EAR INNERVATION The tympanic cavity contains the tympanic plexus and the facial nerve. Branches from the plexus and the facial nerve supply structures within the tympanic cavity but also leave the cavity to supply structures on the face. 27

28 THE PHARYNGOTYMPANIC TUBE THE MIDDLE EAR The pharyngotympanic tube connects the tympanic cavity (anterior wall) to the nasopharynx, where it opens posterior to the inferior nasal meatus It allows the air pressure on either side of the tympanic membrane to equalize. is opened by the expanding girth of the belly of the levator veli pala/ni as it contracts longitudinally, pushing against one wall while the tensor veli pala/ni pulls on the other The nerves of the pharyngotympanic tube arise from the tympanic plexus which is formed by fibers of the glossopharyngeal nerve (CN IX). Anteriorly, the tube also receives fibers from the pterygopala/ne ganglion. 28

29 THE AUDITORY OSSICLES The bones of the middle ear consist of: the malleus, incus, and stapes THE MIDDLE EAR These ossicles are the first bones to be fully ossified during development and are essen/ally mature at birth, unlike other bones, they lack a surrounding layer of osteogenic periosteum They form an osseous chain of three mobile ossicles across the middle ear from: the tympanic membrane to the oval window of the internal ear 29

30 THE AUDITORY OSSICLES THE MIDDLE EAR transfers sound waves across the tympanic cavity from the tympanic membrane to the fenestra ves/buli of the bony labyrinth. The malleus is akached to the tympanic membrane, and the base (footplate) of the stapes is akached to the rim of the fenestra ves/buli. The incus is suspended between them and ar/culates with both bones. 30

31 THE AUDITORY OSSICLES - MALLEUS MALLEUS - iden/fiable parts include: the head of malleus neck of malleus anterior and lateral processes handle of malleus THE MIDDLE EAR MALLEUS The head of the malleus ar/culates with the incus; the tendon of the tensor tympani inserts into its handle near the neck. MALLEUS The malleus func/ons as a lever, with the longer of its two processes and its handle akached to the tympanic membrane. MALLEUS The chorda tympani nerve crosses the medial surface of the neck of the malleus. 31

32 THE AUDITORY OSSICLES - INCUS INCUS is located between the malleus and the stapes. It consists of: the body of incus and the long and short limbs THE MIDDLE EAR INCUS The enlarged body of incus ar/culates with the head of malleus and is in the epitympanic recess. INCUS The long limb extends downward from the body, paralleling the handle of the malleus, and ends by bending medially to ar/culate with the stapes. 32

33 THE AUDITORY OSSICLES - STAPES STAPES The stapes is the most medial bone in the osseous chain and is akached to the oval window. consists of: the head of stapes anterior and posterior limbs the base of stapes THE MIDDLE EAR STAPES The head of stapes is directed laterally and ar/culates with the long process of the incus. STAPES The base of stapes fits into the oval window on the labyrinthine wall of the middle ear. 33

34 THE MIDDLE EAR THE MUSCLES ASSOCIATED WITH THE OSSICLES Two muscles are associated with the bony ossicles of the middle ear: the tensor tympani the stapedius 34

35 THE MIDDLE EAR THE MUSCLES ASSOCIATED WITH THE OSSICLES TENSOR TYMPANI ORIGIN: car/laginous part of pharyngotympanic tube, greater wing of sphenoid, its own bony canal INSERTION: upper part of handle of malleus TENSOR TYMPANI INNERVATION: branch from mandibular nerve V 3 TENSOR TYMPANI FUNCTION: contrac/on pulls handle of malleus medially, tensing tympanic membrane 35

36 STAPEDIUS ORIGIN: akached to inside of pyramidal eminence THE MIDDLE EAR THE MUSCLES ASSOCIATED WITH THE OSSICLES STAPEDIUS INNERVATION: branch of facial nerve VII INSERTION: neck of stapes 36

37 THE INNERVATION OF THE MIDDLE EAR THE MIDDLE EAR The tympanic plexus innervates the mucous membrane lining the walls and contents of the middle ear, which includes the mastoid area and the pharyngotympanic tube. The tympanic plexus is formed by: the tympanic nerve, a branch of the glossopharyngeal nerve [IX], and from branches of the internal carold plexus. Branches from the tympanic plexus supply the mucous membranes of the middle ear, including the pharyngotympanic tube and the mastoid area. The tympanic plexus also gives off a major branch (the lesser petrosal nerve), which supplies preganglionic parasympathe/c fibers to the o/c ganglion 37

38 THE INTERNAL EAR THE INTERNAL EAR The internal ear consists of: a series of bony cavi/es - the bony labyrinth and membranous ducts and sacs - the membranous labyrinth within these cavi/es. All these structures are in the petrous part of the temporal bone between the middle ear laterally and the internal acous/c meatus medially 38

39 The bony labyrinth consists of: the veslbule three semicircular canals the cochlea THE BONY LABYRINTH THE INTERNAL EAR The bony cavi/es are lined with periosteum and contain a clear fluid the perilymph 39

40 THE BONY LABYRINTH THE INTERNAL EAR The bony labyrinth is the fluid-filled space, which is surrounded by the o/c capsule, and is represented by a cast of the o/c capsule a^er removal of the surrounding bone. The veslbular aqueduct leaves the ves/bule, and passes through the temporal bone to open on the posterior surface of the petrous part of the temporal bone. 40

41 THE COCHLEA THE INTERNAL EAR The cochlea is the shell-shaped part of the bony labyrinth that contains the cochlear duct, the part of the internal ear concerned with hearing. The cochlea is a bony structure that twists on itself two and one-half to two and three-quarter /mes around a central column of bone, the modiolus The modiolus contains canals for blood vessels and for distribu/on of the branches of the cochlear nerve. This arrangement produces a cone-shaped structure with a base of cochlea that faces posteromedially and an apex that faces anterolaterally 41

42 THE COCHLEA THE INTERNAL EAR This posi/ons the wide base of the modiolus near the internal acous/c meatus, where it is entered by branches of the cochlear part of the ves/bulocochlear nerve [VIII]. Extending laterally throughout the length of the modiolus is a thin lamina of bone - the lamina of modiolus or spiral lamina Circling around the modiolus, and held in a central posi/on by its akachment to the lamina of modiolus, is the cochlear duct, which is a component of the membranous labyrinth. 42

43 THE COCHLEA THE INTERNAL EAR Akached peripherally to the outer wall of the cochlea, the cochlear duct creates two canals - the scala veslbuli and the scala tympani The scala veslbuli and the scala tympani are con/nuous at the apex through a narrow slit the helicotrema The scala veslbuli is con/nuous with the ves/bule. The scala tympani is separated from the middle ear by the secondary tympanic membrane covering the round window Near the round window is a small channel the cochlear canaliculus. It provides a connec/on between the perilymph-containing cochlea and the subarachnoid space. 43

44 THE MEMBRANOUS LABYRINTH THE INTERNAL EAR The membranous labyrinth is a con/nuous system of ducts and sacs within the bony labyrinth It is filled with endolymph and separated from the periosteum that covers the walls of the bony labyrinth by perilymph The membranous labyrinth, composed of two divisions: the ves/bular labyrinth the cochlear labyrinth 44

45 THE MEMBRANOUS LABYRINTH Consis/ng of two sacs: the utricle the saccule and four ducts: the three semicircular ducts the cochlear duct THE INTERNAL EAR The ves/bular labyrinth and the cochlear labyrinth, consists of more parts than does the bony labyrinth: veslbular labyrinth: utricle and saccule, two small communica/ng sacs in the ves/bule of the bony labyrinth. three semicircular ducts in the semicircular canals. cochlear labyrinth: cochlear duct in the cochlea. 45

46 THE MEMBRANOUS LABYRINTH THE INTERNAL EAR The semicircular ducts open into the utricle through five openings, reflec/ve of the way the surrounding semicircular canals open into the ves/bule. The utricle communicates with the saccule through the utriculosaccular duct, from which the endolympha/c duct arises The saccule is con/nuous with the cochlear duct through the ductus reuniens, a uni/ng duct. 46

47 THE MEMBRANOUS LABYRINTH THE INTERNAL EAR The receptors for auditory and veslbular funclon are located within the membranous labyrinth The utricle and saccule have specialized areas of sensory epithelium called maculae. The hair cells in the maculae are innervated by fibers of the ves/bular division of the ves/bulocochlear nerve. In the maculae, the weight of the otoconial crystals creates a gravita/onal pull on the otoconial membrane and thus on the stereociliary bundles of the sensory cells that are inserted into its base. Because of this, they are able to detect the sta/c orienta/on of the head with respect to gravity. 47

48 THE MEMBRANOUS LABYRINTH THE INTERNAL EAR The primary sensory neurons are in the ves/bular ganglia, which are in the internal acous/c meatus. Fluids located in the membranous labyrinth (endolymph) and osseous labyrinth (perilymph) s/mulate the auditory and ves/bular receptors 48

49 THE INTERNAL EAR THE MEMBRANOUS LABYRINTH - SEMICIRCULAR DUCTS Each semicircular duct has an ampulla at one end containing a sensory area, the ampullary crest The hair cells of the crests, like those of the maculae, s/mulate primary sensory neurons, whose cell bodies are in the ves/bular ganglia. 49

50 THE MEMBRANOUS LABYRINTH - COCHLEAR DUCT THE INTERNAL EAR The cochlear duct is a spiral tube that runs within the bony cochlea The duct is firmly suspended across the cochlear canal between the spiral ligament on the external wall of the cochlear canal and the osseous spiral lamina of the modiolus. The roof of the cochlear duct is formed by the ves/bular membrane. The floor of the duct is also formed by part of the duct, the basilar membrane, plus the outer edge of the osseous spiral lamina. 50

51 THE MEMBRANOUS LABYRINTH - COCHLEAR DUCT THE INTERNAL EAR The receptor of auditory s/muli is the spiral organ of CorL, situated on the basilar membrane. It is overlaid by the gela/nous tectorial membrane. The organ is s/mulated to respond by deforma/on of the cochlear duct induced by the hydraulic pressure waves in the perilymph, which ascend and descend in the surrounding scalae ves/buli and tympani. 51

52 ANATOMY OF HEARING THE EAR Waves of hydraulic pressure created in the perilymph of the ves/bule by the vibra/ons of the base of the stapes ascend to the apex of the cochlea by one channel, the scala ves/buli The pressure waves then pass through the helicotrema and descend back to the basal turn of the cochlea by the other channel, the scala tympani. Here, the pressure waves again become vibra/ons, this /me of the secondary tympanic membrane of the round window, and the energy ini/ally received by the (primary) tympanic membrane is finally dissipated into the air of the tympanic cavity. 52

53 INTERNAL ACOUSTIC MEATUS THE EAR The internal acouslc meatus is a narrow canal that runs laterally for approximately 1 cm within the petrous part of the temporal bone Through the perforated plate of temporal bone pass the facial nerve (CN VII), the ves/bulocochlear nerve (CN VIII) and its divisions, and blood vessels. 53

54 THE FACIAL NERVE THE EAR The facial nerve consists of intracranial (cisternal), intratemporal and extratemporal por/ons. The intratemporal por/on is further divided into: meatal, labyrinthine, tympanic (horizontal) mastoid (ver/cal) segments 54

55 THE FACIAL NERVE THE EAR The meatal porlon enters the porus acus/cus of the internal auditory meatus accompanied by the nervus intermedius, the ves/bulocochlear nerve and the labyrinthine vessels. The labyrinthine segment runs from the fundus of the internal acous/c meatus to the geniculate ganglion, where the nerve makes the first bend The tympanic part ini/ally curves around the oval window niche, then lies just anterior and inferior to the lateral semicircular canal and bends again at the second genu to become the ver/cal or mastoid part. The mastoid part is the longest of the petrous segments and runs from the pyramidal process to the stylomastoid foramen. 55

56 THE FACIAL NERVE The main branch from the geniculate ganglion is the greater petrosal nerve, a branch of the nervus intermedius. THE EAR The greater petrosal nerve passes anteriorly, receives a branch from the tympanic plexus and traverses a hiatus on the anterior surface of the petrous part of the temporal bone. It enters the middle cranial fossa, it is joined by the deep petrosal nerve from the internal caro/d sympathe/c plexus, to become the nerve of the pterygoid canal 56

57 THE FACIAL NERVE The greater petrosal nerve contains parasympathe/c fibres des/ned for the pterygopala/ne ganglion, and taste fibres from the palate. THE EAR The nerve to stapedius arises from the facial nerve in the facial nerve canal behind the pyramidal eminence of the posterior wall of the tympanic cavity and passes forwards through a small canal to reach the muscle. The chorda tympani leaves the facial nerve above the stylomastoid foramen and runs antero-superiorly in a canal to enter the tympanic cavity via the posterior canaliculus. 57

58 THE FACIAL NERVE THE EAR The chorda tympani leaves crosses medial to the upper part of the handle of the malleus to the anterior wall of the tympanic cavity, where it enters the anterior canaliculus. It exits the skull at the petrotympanic fissure. The chorda tympani contains parasympathe/c fibres that supply the submandibular and sublingual salivary glands via the submandibular ganglion and taste fibres from the anterior two-thirds of the tongue. 58

59 THE VESTIBULOCOCHLEAR NERVE THE VESTIBULOCOCHLEAR NERVE CN VIII The ves/bulocochlear nerve carries special afferent fibers for hearing (the cochlear component) and balance (the ves/bular component) The ves/bulocochlear nerve emerges from the cerebellopon/ne angle, between the pons and medulla It courses through the posterior cranial fossa in close associa/on with the facial nerve, nervus intermedius and labyrinthine vessels. 59

60 THE VESTIBULOCOCHLEAR NERVE THE VESTIBULOCOCHLEAR NERVE CN VIII It enters the petrous temporal bone via the porus acus/cus of the internal acous/c meatus, and divides into: an anterior trunk, the cochlear nerve, and a posterior trunk, the ves/bular nerve The veslbular nerve enlarges to form the veslbular ganglion, before dividing into superior and inferior parts, which distribute to the three semicircular ducts and the utricle and saccule The cochlear nerve enters the base of the cochlea and passes upward through the modiolus. 60

61 THE VESTIBULOCOCHLEAR NERVE THE VESTIBULOCOCHLEAR NERVE CN VIII The ganglion cells of the cochlear nerve are in the spiral ganglion at the base of the lamina of modiolus as it winds around the modiolus Branches of the cochlear nerve pass through the lamina of modiolus to innervate the receptors in the spiral organ. 61