Notes on Ana

7/28/2019 Notes on Ana

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NOSE, NASAL CAVITIES AND PARANASAL SINUSES

Cutaneous innervation

The nerve supply to the skin of the nose is by V1 (infratrochlear nerve) andV2 (infraorbital nerve; Clemente plate 504; Grant p. 630; Netter 3e 20, 4e 24).

The innervation of the tip of the nose is by the external nasal nerve, an anterior ethmoidal branch of the nasociliary nerve (V1) running from the root of the nose to the tip of the nose.

Loss of sensation to the tip of the nose may be due to an intracranial,intraorbital or ethmoidal air sinus disorder affecting V1 pathway from the trigeminal ganglion.

Bony landmarks

The paired nasal bones articulate with the frontal bone and frontal processes of the maxillary bones (Clemente plate 522 fig. 825; Grant p. 690; Netter 3e 32, 4e 36).

The central septal cartilage connects with the superior lateral cartilages articulating with the nasal bones (Clemente plate 524 fig. 829; Grant p. 690; Netter 32, 4e 36).

Alar cartilages are supported by the septal cartilage.

NASAL CAVITIES

The nares (nostrils) open into the right and left nasal cavities separated by the septum.

The choanae are the posterior apertures leading to the nasopharynx (Clementeplate 552; Grant p. 616, 790-791; Netter 3e 33, 4e 37).

Floor of nasal cavity:

palatine processes of the maxillaand horizontal plates of the palatine bone.

Roof of nasal cavity is composed of (Clemente plate 523; Grant p. 691; Netter 3e34-35, 4e 38-39):

Anterior part: slope of the nasal bonesIntermediate part: cribriform plate of ethmoid bonePosterior part: anterior and inferior aspects of the body of the sphenoid bo

ne.

Nasal septum (Clemente plate 524 fig. 829; Grant p. 691; Netter 3e 35, 4e 39):

The perpendicular plate of the ethmoid bone and the vomer bone may articulate with each other posteriorly.

The septal cartilage intervenes between bony elements of the septum, forming

support for the midline ridge of the nose, tip and columella (between nares from tip of the nose to anterior nasal spine of the maxilla).

Deviation of the nasal septum is most frequent between the vomer and the septal cartilage.

Lateral wall (Clemente plate 525; Grant p. 691; Netter 3e 34, 4e 38)

Superior, middle and inferior nasal conchae and their corresponding meatuses.

Sphenoethmoid recess lies superior to the superior concha.


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Vestibule, just inside each naris, is lined by skin.Atrium, inferior to nasal bones, is lined by mucoperiosteum.

The inferior concha

is a separate bone articulating with maxilla, lacrimal and palatine bones onthe lateral wall of the nasal cavity (Clemente plate 523; Grant p. 691; Netter3e 34, 4e 38).

Its meatus contains the opening of the nasolacrimal duct draining tears frommedial aspect of the orbit into the nasal cavity (Clemente plate 507 fig. 798;Grant p. 695; Netter 3e 34, 78, 4e 37-38, 82 ).

The posterior extent of the nasal cavity is adjacent to the opening of the auditory tube in the nasopharynx (Clemente plate 525; Grant p. 695; Netter 3e 33, 4e37).

The middle concha is a process of the ethmoid bone (Clemente plate 523; Grant p.691; Netter 3e 33, 4e 38) and it overlies the middle meatus.

Paranasal air sinuses open into this meatus: the hiatus semilunaris (Clemente plate 522 fig. 826; Grant p. 695; Netter 3e 33, 4e 37) opens on the wall of the middle meatus between the unciform process of the ethmoid bone and the ethmoid bulla.

Frontal sinus drains into the superior aspect of the hiatus semilunaris (Clemente plate 522 fig. 826; Grant p. 695; Netter 3e 33, 4e 37).Anterior and middle ethmoidal air sinuses drain through openings of the ethm

oidal bulla on superoposterior aspect of the hiatus semilunaris.Maxillary air sinus has its ostium directly inferior to the ethmoid bulla wi

thin the hiatus semilunaris.

The superior concha is also a process of the ethmoid bone (Clemente plate 523; Grant p. 691; Netter 3e 34, 4e 38).

It overlies the superior meatus receiving the opening of the posterior ethmoidal air cells (Clemente plate 525 fig. 832; Grant p. 695; Netter 3e 32, 33, 4e38).

Superior to the superior concha is the spheno-ethmoidal recess where the sphenoid air cells drain into nasal cavity.NERVE SUPPLY TO THE NASAL CAVITY

The mucosa of upper nasal cavity is innervated by the olfactory (I) and trigeminal (V1; anterior ethmoidal) nerves (Clemente plate 524 fig. 830; Grant p. 692; Netter 3e 38-39, 4e 42-43).

The anterior ethmoidal nerve carries general sensation (pain, temperature, touch and pressure).

Most of the general sensation of the lateral wall and nasal septum is mediated b

y V2, which is associated with the pterygopalatine ganglion (Clemente plate 526;Grant p. 692; Netter 3e 39, 4e 43).

The pterygopalatine ganglion receives the preganglionic parasympathetic fibers of the superficial (greater) petrosal nerve (VII; Clemente plate 527; Grant p. 692, 700, 831; Netter 3e 39, 117, 4e 43, 123).

The postganglionic parasympathetic neurons send secretomotor fibers to glands above the floor of the mouth.

Terminal branches of the infraorbital nerve (Grant p. 692; Netter 3e 38, 4e 42)


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also enter the vestibule of the nose from the skin covering the nares.

A small branch from the anterior superior alveolar nerve also innervates the anterior nasal mucosa of the inferior meatus (Grant p. 692; Netter 3e 38, 4e 42).

The mucosa on the lateral wall of the nose is innervated by branches of the descending greater palatine nerve from the inferior pole of the pterygopalatine ganglion.

Superior and inferior posterior lateral nasal nerves run in the mucoperiosteum covering the conchae and the meatus.

The nasal septum mucosa is innervated by the nasopalatine nerve (Clemente plate524 fig. 830; Grant p. 692; Netter 3e 39, 4e 43).

It enters the nasal cavity from the pterygopalatine fossa through the sphenopalatine foramen

and descends on the median nasal septum.The terminal branch leaves the nasal cavity via the incisive foramen (Clemen

te plate 524 fig. 830; Grant p. 692; Netter 3e 39, 4e 43).

The sympathetic innervation of the nasal cavities comes from the superior cervical ganglion. These postganglionic fibers reach the nose via the nerve of the internal carotid artery (Clemente plate 527; Grant p. 701; Netter 3e 40, 4e 44) and

the deep petrosal nerve of the pterygoid canal. In the pterygopalatine fossa, they join with terminal branches of the maxillary artery and are vasomotor to blood vessels in the nasal cavity and palate.

BLOOD SUPPLY OF THE NASAL CAVITY

The sphenopalatine artery

arises from the maxillary artery in the pterygopalatine fossa (Clemente plate 526; Grant p. 693; Netter 3e 36-37, 4e 40-41).

It enters the nasal cavity with the nasopalatine nerve and supplies upper 2/3 of the nasal septum.

It then anastomoses with the greater palatine artery ascending through the i

ncisive foramen.

The site of anastomosis is a frequent area of hemorrhage (epistaxis or nosebleed).

The lateral walls of the nasal cavity are supplied by blood vessels accompanyingthe terminal branches of the anterior ethmoidal nerve and the greater palatinenerve and they have the same name (Clemente plate 526; Grant p. 693; Netter 3e 37, 4e 41).

The venous drainage of the nose parallels the arterial supply and forms a network overlying the inferior and middle conchae.

The erectile tissue overlying the conchae humidifies and warms the inspired airin the upper respiratory passage.PARANASAL AIR SINUSES

The sphenoid (Clemente plate 522 fig. 826; Grant p. 694; Netter 3e 44, 4e 48-49), ethmoid (Clemente plate 528; Grant p. 696; Netter 3e 44-45, 4e 48-49), frontal (Clemente plate 529; Grant p. 696; Netter 3e 44, 4e 48-49) and maxillary are paired but asymmetrical.

They are lined with respiratory epithelium which becomes converted to stratified squamous epithelium with chronic respiratory irritation. This may lead to c


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hronic sinusitis.

Sinus drainage

Sphenoid air sinuses drain into the sphenoethmoidal recess (Clemente plate 525 fig. 832; Grant p. 696; Netter 3e 45, 4e 37). A surgical approach to the pituitary may be done through these air sinuses and the nasal cavities.

Ethmoidal air sinuses (anterior, middle and posterior).

Anterior and middle drain into middle meatus by openings of the ethmoidal bulla (Clemente plate 522 fig. 826; Grant p. 695; Netter 3e 34, 4e 37).

Posterior ethmoidal air cells drain into the superior meatus.

Frontal sinus drains via the infundibulum into the superior extension of the hiatus semilunaris (Clemente plate 525 fig. 832; Grant p. 695; Netter 3e 45, 4e 37).

Maxillary sinus drains into the middle meatus through the hiatus semilunaris. The air sinus has a floor at the level of the hard palate (Clemente plate 529; Grant p. 698; Netter 3e 45, 4e 49) and since the ostium is more superiorly located(Clemente plate 525 fig. 832; Grant p. 696, 698; Netter 3e 45, 4e 49), there isoften drainage problems. The nerve supply is by the posterior and middle superior alveolar nerves (V2; Clemente plate 527 fig. 836; Grant p. 700; Netter 3e 41,

4e 45).

Mastoid air sinuses (Clemente plate 527 fig. 836; Grant p. 710; Netter 3e 89, 4e94) drain into the nasal cavity via the middle ear and auditory tube.

updated 11/28/2009THE ORAL CAVITY AND CONT

ENTS

The VESTIBULE

is bounded by lips and cheeks,is lined with non-keratinized stratified squamous epithelium.

the parotid papilla is in the superior vestibule, opposite the 2nd upper molar tooth (Netter 3e 47, 4e 51).is vascularized by the superior and inferior labial arteries from the facial

artery (Clemente plate 474; Grant p. 632; Netter 3e 32, 4e 36) . These arteriesanastomose freely with their contralateral counterparts. Because of these profuse anastomoses, lip bleeding is controlled by grasping the injured lip between the fingers to stop the blood flow.

Nerve supply of the vestibule:

The orbicularis oris and buccinator muscles are innervated by cranial nerveVII (facial nerve; Clemente plate 469; Grant p. 629; Netter 3e 21, 4e 25).

The skin and mucosa of the upper lip, cheek and vestibule are innervated by

the anterior, middle and posterior superior alveolar nerves from V2 (Clemente plate 527; Grant p. 700; Netter 3e 42, 4e 45).

The skin and mucosa of lower lip and adjacent anterior vestibule are innervated by the mental nerve (V3; Clemente plate 476; Grant p. 630-631, 671; Netter 3e 42, 4e 46).

The mucosa of the inferior vestibule adjacent to the cheek is innervated bythe long buccal (buccinator; Grant p. 630, 668; Netter 4e 46) nerve from the anterior division of V3.

ORAL CAVITY


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The roof is formed by the hard and soft palates with the midline uvula (Clemente plate 530 fig. 843; Grant p. 682; Netter 3e 48, 52; 4e 51).

The posterior border is formed by the pillars of the fauces (Clemente plate530; Grant p. 676; Netter 3e 54, 4e 51, 58)

The floor is formed by the tongue divided into anterior 2/3 and posterior 1/3 by the palatoglossal arch, the V-shaped sulcus terminalis and circumvallate papillae (lying anterior to the sulcus; Clemente plate 539; Grant p. 676; Netter 3e 54, 4e 58).

The lingual frenulum (Clemente plate 532 fig. 847; Grant p. 680; Netter 3e 47, 4e 51) is found on the undersurface of the tongue with openings of the ductsof the submandibular gland (Clemente plate 533 fig. 850; Grant p. 680; Netter 3e47, 4e 51).

In examination of the tongue, grasp the tip of tongue with gauze and pull the tongue out of the mouth. Examine the lateral aspects of the anterior 2/3 of the tongue. This is a common site for cancer of the tongue.

FLOOR OF THE MOUTH (SUBLINGUAL REGION)The sublingual gland (Clemente plate 532 fig. 847, plate 543; Grant p. 680-681;Netter 3e 57, 4e 61):

lies on the lingual aspect of the body of the mandible, deep to the plica sublingualis (sublingual fold), which is the posterolateral continuation of the li

ngual frenulum.It has a row of 15 or 16 ("middle-teens") ducts that empty into the floor ofthe mouth on the plica sublingualis.

The duct of the submandibular gland and the lingual nerve lie on the medialsurface of the sublingual gland.

The mylohyoid muscle lies inferior to the sublingual gland.The sublingual gland is innervated by postganglionic parasympathetic fibers

reaching the gland via its sensory nerve, the lingual nerve (V3). Preganglionicparasympathetic fibers run with the chorda tympani (VII) synapsing in the submandibular ganglion (Clemente plate 479; Grant p. 831; Netter 3e 41, 4e 46).

The lingual nerve

provides the general sensory (pain, touch and temperature) modality to the anterior 2/3 of the tongue and the floor of the mouth (Clemente plate 532 fig. 848; Grant p. 680-681, 829; Netter 3e 55, 4e 59).

also carries chorda tympani which has special taste fibers and secretomotorfibers of VII.

enters the floor of the mouth on the medial mandible next to the 3rd molar tooth (Clemente plate 533 fig. 850; Grant p. 680-681; Netter 3e 42, 4e 46). It isthus vulnerable in extraction of the wisdom teeth.

Preganglionic parasympathetic fibers leave the lingual nerve to synapse in the submandibular ganglion (Clemente plate 535 fig. 855; Grant p. 680, 840; Netter 3e 42, 4e 133). Postganglionic parasympathetic fibers rejoin the lingual nerveto reach the sublingual salivary gland. The submandibular ganglion is thus suspended from the main trunk of the lingual nerve.

The lingual nerve is:

superior to the mylohyoid muscle in the floor of the mouth (Clemente plate 479; Grant p. 681; Netter 3e 42, 4e 46).

lateral to the submandibular duct (Clemente plate 479; Grant p. 680-681, 780; Netter 3e 42, 4e 46),

and medial to the sublingual gland (Clemente plate 479; Grant p. 680; Netter3e 56, 4e 60).

Subsequently, it passes inferior and then medial to the submandibular duct t


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o ascend into the body of the tongue (Clemente plate 533 fig. 850; Grant p. 680-681; Netter 3e 55, 4e 59).

The chorda tympani provides taste fibers which supply the anterior 2/3 of the tongue. The cell bodies are in the geniculate ganglion in the middle ear (Clementeplate 573; Grant p. 709, 831; Netter 3e 117, 4e 135).

The hypoglossal nerve enters the floor of the mouth on the lateral aspect of thehyoglossus muscle, above the hyoid bone and the mylohyoid muscle (Clemente plate 535 fig. 855; Grant p. 681, 780; Netter 3e 55, 4e 59). Cranial nerve XII liesinferior to the lingual nerve and is purely motor to the muscles of the tongue.

Test cranial nerve XII by protrusion of the tongue. Deviation is toward theside of the lesion.

The tongue

allows for mastication, swallowing, speech and taste.The anterior 2/3 (body or oral part) is derived from the ectodermal stomodeu

m.The posterior 1/3 (pharyngeal part or root) is derived from the endodermal f

oregut.These 2 parts are separated by the sulcus terminalis posterior to the circum

vallate papillae (Clemente plate 539; Grant p. 676; Netter 3e 52, 4e 58).

The sulcus terminalis is oriented posteriorly and the foramen cecum can be found at the tip of the V-shaped sulcus terminalis. This is the point of origin of the thyroid gland.

Lingual tonsils are located posterior to the sulcus terminalis.

Mucous membrane of the tongue:

The papillae (filiform, fungiform, circumvallate and foliate) are innervatedby cranial nerve VII via the chorda tympani (anterior 2/3) and by IX (posterior1/3; (Clemente plate 539; Grant p. 676; Netter 3e 54, 4e 58).

The taste buds in the epiglottis and the pharyngeal walls are innervated byX.

The taste buds in the palate are innervated by cranial nerve VII via the gre

ater petrosal nerve. Branches from the latter are distributed by the greater andlesser palatine nerves (Clemente plate 532 fig. 849; Grant p. 683, 831; Netter3e 48, 4e 52).

Muscles of the tongue

1) The 3 extrinsic muscles of the tongue change the position of the tongue.

The genioglossus attaches to the superior genial tubercles and protrudes thetongue (Clemente plate 540; Grant p. 679-680; Netter 3e 59; 4e 63).

The hyoglossus depresses the tongue.and the styloglossus retracts the tongue.

2) The intrinsic (longitudinal, transverse and vertical) muscles change the shape of the tongue.

The lingual artery:

is a branch from the external carotid artery and supplies the tongue.courses anteriorly on the middle constrictor (Clemente plate 460 fig. 724; G

rant p. 763, 781; Netter 3e 53, 4e 59, 69) parallel with cranial nerve XII.The hyoglossus muscle intervenes between cranial nerve XII (lateral) and the

lingual artery (medial). The lingual artery is the only major structure medial


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to the hyoglossus muscle (Clemente plate 535 fig. 855; Grant p. 679-680, 780-781; Netter 3e 55, 4e 59).

Dorsal lingual branches from the lingual artery are given to the dorsum of the tongue

and deep lingual arteries are given to the body of the tongue.Other terminal branches supply the genioglossus muscle and the sublingual gl

and.Lymphatics follow arteries and drain to both right and left jugular lymphati

c trunks of the neck (Clemente plate 455; Grant p. 676, 716; Netter 3e 68, 4e 73).

TEETH

In each adult jaw (Clemente plates 544, 545; Grant p. 685-689; Netter 3e 52-53,4e 56-57):

4 incisors2 canines4 premolars6 molars

Nerve supply of teeth and gums (Clemente plate 542 fig. 866; Grant p. 687; Netter 3e 41, 42, 4e 45-46):

V2 supply the teeth and gums of the maxillary arch.

The molar teeth are supplied by the posterior superior alveolar nerve from the pterygopalatine fossa.

The bicuspids (premolars) are innervated by the middle superior alveolar nerve from the infraorbital nerve.

The canines and incisors are innervated by the anterior superior alveolar nerve from the infraorbital nerve

The gums on the palatal surface are innervated by the nasopalatine nerve (incisors) and greater palatine nerve (bicuspids and molars; Clemente plate 527; Grant p. 683; Netter 3e 39, 4e 52).

V3 supplies teeth and gums of mandibular arch.

The inferior alveolar (dental) nerve innervates all the teeth in the mandible.

The gums of the molars and bicuspids are innervated by the long buccal nerveThe gums of the incisors are innervated by the mental nerve.The lingual gums are innervated by the lingual nerve.

updated 10/28/2009THE EAR AND THE TEMPORAL

BONEThe EXTERNAL EAR

is formed by the:

Auricle (Clemente plate 564; Grant p. 703; Netter 3e 87-88, 4e 92-93): is made of elastic cartilage and is continuous with the cartilage of the external acoustic meatus and the lobule (which is formed by loose connective tissue).

External acoustic meatus (Clemente plate 566 fig. 921; Grant p. 703; Netter3e 87, 4e 92)

The innervation of the skin of the ear:

The superior portion is innervated by V3 via the auriculotemporal nerve (Cle


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mente plate 468; Grant p. 627, 703; Netter 3e 20, 4e 24);The inferior portion including lobule is innervated by fibers of the great a

uricular nerve from the cervical plexus (C 2, 3);The external acoustic meatus and the skin surrounding the opening (concha) a

re innervated by the vagus nerve (X) for general sensation (Clemente plate 468;Grant p. 703; Netter 3e 20, 4e 24).

Neurological examination of the skin of ear can determine the status of theupper spinal cord (great auricular nerve, C 2, 3), the medulla (vagus X) and thepons (trigeminal V).

The external acoustic meatus (Clemente plate 566 fig. 921; Grant p. 703, 705; Netter 3e 87, 4e 92):

extends from the concha to the tympanic membrane.Lateral cartilaginous 1/3 (lined with hair, sebaceous glands and ceruminous

glands)Medial bony 2/3 (thin stratified squamous epithelium, also lining external s

urface of tympanic membrane).The auricular branch of the vagus (X) provides the sensory innervation (Clem

ente plate 479; Grant p. 703; Netter 3e 20, 120, 4e 24, 126).

The MIDDLE EAR or TYMPANUM

Sound waves create vibrations on the tympanic membrane moving the 3 bony ossicles (malleus, incus and stapes) which in turn vibrate the oval window (fenestra vestibuli) on the medial wall of the middle ear: this is an amplification system (Clemente plate 566; Grant p. 704; Netter 3e 88, 4e 93, 95).

The middle ear is a modified bony sinus in the petrous portion of the temporal bone. It communicates with the mastoid air cells through the aditus to the mastoid antrum(Clemente plate 569; Grant p. 710, 713; Netter 3e 89, 4e 94) and with the nasopharynx through the auditory tube (pharyngotympanic tube; Clemente plate 566; Grant p. 704-705; Netter 3e 87, 4e 92, 94).

The tympanic cavity and its walls:

The roof is a thin layer of petrous temporal bone (Clemente plate 566; Grantp. 708-709; Netter 3e 87, 4e 92) separating the middle cranial fossa from the middle ear.

The space below the roof is the epitympanic recess (Clemente plate 566;Grant p. 708; Netter 3e 88-89, 4e 92-93) for the articular joint of the head ofthe malleus and body of the incus.

The floor of the tympanic cavity rests upon the superior jugular bulb (Clemente plate 569 fig. 928, plate 573 fig. 935; Grant p. 710-711; Netter 3e 87, 4e 92).

Where the internal carotid artery (moving anteriorly) diverges from theinternal jugular vein (moving posteriorly), the cranial nerves IX and X send branches into the bony tympanic floor (Clemente plate 571 fig. 932; Grant p. 710; N

etter 3e 89, 4e 94, 125).Roof and floor converge anteriorly to form the auditory tube which is di

vided by the processus cochlearis (Clemente plate 569; Grant p. 711; Netter 3e 88-89, 4e 92-94) into:

a superior compartment containing the tensor tympani muscle. The tensor tympani inserts into the handle of the malleus.

and a lower compartment which joins with the cartilaginous portion of the auditory tube.

The lateral wall of the tympanic cavity is closed by the tympanic membrane.


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The ascending carotid artery is associated with the anterior wall of the tympanic cavity, separated by a thin layer of bone (Clemente plate 571, fig. 932; Grant p. 710; Netter 3e 89, 4e 94).

Pulsations may be heard by the patient in some clinical disorders.

The posterior wall of the tympanic cavity contains a tunnel, the aditus, connecting to the mastoid antrum.

Fluid from the mastoid air cells drain via the aditus into the tympaniccavity and then into the auditory tube and the nasopharynx.

Fluid may collect within the tympanic cavity if the auditory tube is obstructed due to an upper respiratory airway infection.

The VIIth cranial nerve enters the posterior wall below the aditus (Clemente plate 569 fig. 928; Grant p. 708, 710; Netter 3e 89, 4e 94) and exits fromthe base of the temporal bone via the stylomastoid foramen (Clemente plate 571 fig. 932; Grant p. 616, 712-713; Netter 3e 89, 4e 94).

The chorda tympani arises from the facial nerve within the posterior wall of the middle ear, courses over the eardrum along the lateral wall (Clemente plate 569; Grant p. 708, 711; Netter 3e 89, 4e 94), and exits via the petrotympanic fissure into the infratemporal fossa.

The pyramid is also located in the posterior wall. The apex of the pyramid has an orifice through which the tendon of the stapedius passes to insert onthe neck of the stapes (Clemente plate 570; Grant p. 708; Netter 3e 89, 4e 93-94).

The stapedius acts to retract the stapes from the oval window and re

flexively attenuates loud sound. It is innervated by cranial nerve VII and Bell's palsied patients may complain of sensitivity to loud sounds (hyperacusis).

The medial wall of the tympanic cavity faces the inner ear contained withinthe petrous portion of the temporal bone.

It has the promontory at its center, overlying the first turn of the cochlea. Within the mucosa covering the promontory is the tympanic plexus where fibers of VII, IX and X intermingle (Clemente plates 570, 571; Grant p. 708, 710; Netter 3e 89, 4e 93). Through this plexus will pass:

sensory fibers to the external and middle earand preganglionic parasympathetic fibers for the greater (Clemente p

late 571 fig. 932; Grant p. 834-835; Netter 3e 89, 4e 123, 125) and lesser petrosal nerves.

Posterior and superior to the promontory are the oval window for the foot ofthe stapes, the canal for the facial (VIIth cranial) nerve and the prominence of the lateral semicircular canal (Clemente plates 570, 571; Grant p. 708, 710; Netter 89).

The shape of the oval window matches the footplate of the stapes.The canal of facial nerve is horizontal and connects the internal auditory m

eatus to the descending canal of VII in the posterior wall.

Posterior and inferior to the promontory is the round window or fenestra cochleae (Clemente plate 570 fig. 930; Grant p.710; Netter 89-91), closed by a membrane(Netter 4e 94).The tympanic membrane

is circular (Clemente plate 567; Grant p. 706; Netter 3e 88, 4e 93-94)is set in a sulcus in the tympanic boneis oriented laterally, anteriorly and inferiorly ("catches sounds from the g

round as one advances").is lined with epidermis (ectodermal) laterally and mucous membrane (endoderm

al) medially.The handle of the malleus is attached to the tympanic membrane.The superior pars flaccida of the eardrum attaches to the lateral process of

the malleus.The chorda tympani lies posterior to this pars flaccida and must be avoided


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in puncturing the eardrum to drain the middle ear.

3 bony ossicles

(Clemente plate 568; Grant p. 707; Netter 3e 88, 4e 93-94)

2 synovial joints (between malleus and incus; between incus and stapes; may be affected by otosclerosis resulting in deafness):

Malleus has a head, neck, manubrium with lateral process and an inferiortip. The anterior process of the malleus is attached to a stabilizing ligament(Clemente plate 568 fig. 926; Grant p. 708; Netter 3e 88-89, 4e 93-94).

Incus: The body of the incus articulates with the malleus at the malleoincudal (incudomalleolar) joint (Clemente plate 568 fig. 926; Grant p. 707; Netter 3e 88, 4e 93-94).

Short crus (process) attaches via a ligament to the posterior wall of the epitympanic recess (Clemente plate 568 fig. 925; Grant p. 709; Netter 3e 89, 4e 94).

Long crus is vertically oriented and descends into the tympanic cavity. It has a lenticular process, which articulates with the head of thestapes.

Stapes has a head, neck, posterior and anterior limbs and footplateattached to the oval window by an annular ligament.

The role of the middle ear is to transfer vibratory sounds from the air to a fluid (perilymph):

Vibratory surface of eardrum is 55 mm2 .Footplate is 3.2 mm2 .Hydraulic ratio between membrane and footplate is 17:1.

Muscles of the ossicles: the contraction of either of these muscles attenuate sound by decreasing the movement of ossicles.

1) The tensor tympani (Clemente plates 569, 570; Grant p. 708; ; Netter 3e 88-89, 4e 93-94) in the auditory canal runs around the processus cochleariformis to attach to the handle of the malleus: the contraction tenses the eardrum by pullin

g medially. It is innervated by a branch of V3 as it exits foramen ovale.

2) The stapedius in the pyramid of the posterior wall, inserts into the neck ofthe stapes. The contraction pulls the foot plate away from the oval window to dampen the sound. It is innervated by VII.The INNER EAR

is a bony labyrinth (Clemente plates 574-575; Grant p. 704-705, 714; Netter 3e 90-91, 4e 95) containing a membranous labyrinth.

The bony labyrinth consists of:

the cochlea,

the vestibuleand the semicircular canals.

1) The cochlea is shaped like a snail shell with 2.5 turns. Vibrations fromthe perilymph of the vestibule is communicated to the fluids of the cochlea stimulating the hearing receptors of the inner ear.

2) The vestibule lies between the cochlea and semicircular canals, communicating with both chambers. It communicates with the tympanic cavity via the oval window (fenestra vestibuli).


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3) The 3 semicircular canals: anterior (superior), posterior and lateral (horizontal). They lie in 3 planes like the corner of a room. Their function is tomaintain balance.

The membranous labyrinth (Clemente plate 575; Grant p. 704, 714; Netter 3e 90, 4e 95-96) is surrounded by perilymph and is formed by the cochlear duct, saccule,utricle and 3 semicircular canal ducts.

The ductus endolymphaticus passes from saccule and utricle through a canal in the petrous bone, the vestibular aqueduct, to a fissure lateral to the internal auditory meatus. It acts as a safety expansion, the endolymphatic sac being placed extradurally.

Fluid waves from the perilymph are communicated to the endolymph of the cochlear duct for hearing.

Angular acceleration of endolymph in semicircular canals shifts the endolymph in the semicircular ducts and stimulate the vestibular receptors in the ampulla of the semicircular canal.

The utricle (for detecting movements in the sagittal plane) and the saccule(for detecting movements in the coronal plane) are for head movements detection.This is based on gravitational forces acting on their receptor mechanisms.

VIIIth cranial (Vestibulocochlear) nerve

(Grant p. 715; Netter 3e 118, 4e 124):

Test hearing by using a tuning fork placed against the mastoid process:

If the eardrum and bony ossicles are impaired, then the bony conduction should be heard normally. But if VIII is impaired then total deafness is the result.

Test balance by having patient stand with feet together and eyes closed. Ifthe vestibular portion of VIII is defective then the patient will fall to the lesioned side.

The blood supply of the inner ear enters the internal acoustic meatus with VII and VIII: This labyrinthine artery is a branch of the anterior inferior cerebellar artery (Clemente plate 493, 574-575; Grant 647; Netter 3e 132-133, 4e 136, 139). It may be affected by strokes in the vertebral arterial system.VIIth cranial (Facial) nerve:

is the nerve of the 2nd pharyngeal arch to the muscles of facial expression,stylohyoid, posterior belly of the digastric and stapedius.

also carries the fibers of the nervus intermedius (intermediate nerve) for taste (special sensory) and preganglionic parasympathetic fibers to all glands ofthe face, except the parotid gland.

The facial (VIIth cranial) nerve:

runs through the internal auditory meatus with VIII (Clemente plate 574; Grant p. 709; Netter 92),

lies above VIII in the canal, above the vestibule of the bony labyrinth,bends on the medial wall of the middle ear and forms the genu with the genic

ulate ganglion,and courses to the posterior wall to descend through the facial canal and ex

it through the stylomastoid foramen (Clemente plate 573; Grant p. 710-711; Netter 3e 89, 4e 94).


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The geniculate ganglion contain the cell bodies for the taste fibers. There is no synapse in the geniculate ganglion.

The greater (superficial) petrosal nerve (Clemente plates 574-575; Grant p. 709-710; Netter 3e 89, 4e 94) branches from the geniculate ganglion, pierces the anterior wall of tympanic cavity, enters the middle cranial fossa. It carries tastefibers for the palate, and secretomotor fibers for glands in the roof of the oral cavity, the nasal cavity and the orbit.

The descending part of VII gives off a motor branch to the stapedius and the chorda tympani (Clemente plate 572 fig. 934; Grant p. 831; Netter 3e 89, 4e 94).

The chorda tympani runs between the handle of the malleus and the vertical process of the incus (Clemente plate 569; Grant p. 708; Netter 3e 89, 4e 94) to exitinto the infratemporal fossa (Clemente plate 479; Grant p. 669; Netter 3e 42, 4e46) via the petrotympanic fissure. It carries taste fibers from the anterior 2/3 of the tongue and secretomotor fibers to the submandibular ganglion.

Notes on Ana

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