THE EAR.ppt

THE EAR BY DR. A.U. AGU 1  Introduction The ear is the organ of hearing & balancing. Defined as: A distance receptor for the collection, conduction, modification, amplification & analysis of complex waves of sound. 2 ...

THE EAR BY DR. A.U. AGU 1  Introduction The ear is the organ of hearing & balancing. Defined as: A distance receptor for the collection, conduction, modification, amplification & analysis of complex waves of sound. 2  Has 3 parts External ear Middle ear Internal ear 3  External ear Consists of: – The auricle (pinna) – The external acoustic meatus (EAM) 4  The auricle (pinna) Is on the side of the head Made up of cartilage covered with skin Arranged in patterns of various elevations & depressions 5  Helix (the large outside rim of the pinna) – extends inferiorly at the fleshy lobule (only part that is not supported by cartilage) Antihelix – curved prominence, parallel & anterior to the posterior part of helix – Divides above into 2 crura Scaphoid fossa – curved depression blw helix & antihelix 6  Concha – hollowed centre of the auricle EAM takes off from the depth of the concha Tragus – anterior to the opening & in front of the concha, opposite it & above the lobule is the antitragus. 7  Muscles Extrinsic mzs – – Anterior auricular – Superior auricular – Posterior auricular Attach the auricle to the scalp & skull N/S – facial n A/S – posterior auricular a 8 Intrinsic mzs – Helicis mj & mi – Trigicus – Antitrigicus – Transverse & oblique auricular mzs N/S – facial n 9 E.A.M. A sinus tube that extends from the concha to the tympanic membrane (TM). 2.5cm from concha & 4cm from tragus Has 2 parts; – Cartilaginous (lateral 1/3) – Osseous (medial 2/3) S-shaped curve. 1st , anteromedial & slightly up (pars externer) Then posteromedial & up (pars media), lastly anteromedial & slightly down (pars interna). 10 Bony part Formed by tympanic part of temporal bone 16mm long & narrower than the cartilaginous. C-shaped in cross section (gap in C is applied to the undersurface of squamous & petrous part 11 Cartilaginous part 8mm long C-shaped & the gap is filled with fibrous tissue Contains hairs, sebaceous & ceruminous glands. EAM is narrowest at the isthmus & has 2-3 fissures in the anterior part – fissure of santorini 12 Nerve Supply – Anterior & superior walls – auriculotemporal branch of mandibular n – Post & inferior walls – auricular branch of vagus n A/S – – posterior auricular & superficial temporal arteries. – Deeper part may receive from maxillary a. V/D – corresponding v L/D – – Occipital – Preauricular – Superficial cervical nodes 13 Applied anatomy Otitis media Foreign body impaction Inflammation 14 Tympanic membrane Separates the EAM from the middle ear Thin & semi-transparent Oval but somewhat broader above than below Lies oblique at an angle of 55 with the meatal floor Longest anteroinferior diameter is 9- 10mm & its shortest is 8-9mm. Around the periphery, anulus attaches it to the tympanic sulcus 15  Anterior & posterior malleolar folds pass to the lateral process of the malleus Pars flaccida (small triangular part) lies above the fold & is lax & thin. Pars tensa (major part) is taut Inner surface of the T.M. is convex & the point of maximum convexity is the UMBO N/S – auriculotemporal n, vagus n (outer), glosopharyngeal n (inner) A/S – deep auricular a (outer), stylomastoid a (inner) 16 Middle ear Is an air space in the temporal bone that contains the ossicles Transmit sound vibration from the T M to the inner ear. The cavity of the middle ear is the tympanic cavity The tympanic cavity is about 15mm in both anteroposterior & vertical diametres Has the shape of biconcave lens 17 Walls of tympanic cavity  Lateral (membranous) wall Largely by T M & about 10mm upward extension into the epitympanic recess 18 Roof (Tegmental wall) Is the tegmen tympani Consists of a thin layer of petrous bone that separate middle ear from middle cranial fossa Floor (jugular wall) Bone above jugular fossa 19 Posterior (mastoid)wall Deficient above (aditus to the mastoid antrum) Below the aditus is a hollow cone that project into the tympanic cavity Another feature is the fossa incudis – a depression in the lower & posterior part of the epitympanic recess that contain the process of incus 20 Anterior wall Only partially complete Lower part consists of layer of bone that separates the T cavity from ICA Superiorly is an opening for pharyngotympanic tube & small opening for canal for tensor tympanic mz 21 Medial (labyrinthine) wall Features are Promontory (formed by basal coil of cochlea) Oval window(fenestra vestibuli) – occupied by base of stape Round window(fenestra cochlea) Facial nerve prominence 22 Auditory ossicles Bones of middle ear: – Malleus – Incus – Stape Form chain from TM to the inner ear. 23 Malleus (mallet) Incus (anvil) Largest & 8–9 mm long Consists of body, long & Attached to TM short limbs Has head, neck, handle, anterior & lateral processes 24 Stape (stirrup) Most medial Attached to the oval window Has; head, base, anterior & posterior limb. 25  Intratympanic muscles Tensor tympani - A long slender mz occupies the bony canal above the osseous part of the pharyngotympanic tube. O - cartilaginous part of the pharyngotympanic tube & the adjoining region of the greater wing of the sphenoid, as well as from its own canal. 26  I - handle of the malleus, near its root. B/S - middle meningeal artery. N/S - mandibular division of the trigeminal nerve via branch of the nerve to medial pterygoid Actions - draws the handle of the malleus medially, & so tenses the TM helps to damp sound vibrations: its action also pushes the base of the stapes more tightly into the fenestra vestibuli. 27  Stapedius O - the pyramidal eminence on the posterior wall of the tympanic cavity. I - posterior surface of the neck of the stapes. The muscle is of an asymmetric bipennate form. B/S - posterior auricular, anterior tympanic & middle meningeal arteries. N/S - branch of the facial nerve Actions - helps to damp down excessive sound vibrations. It opposes the action of tensor tympani Paralysis of stapedius results in hyperacusis. 28  Mastoid antrum & air cells A cavity continuous with collection of air-filled space (mastoid air cell) Lies behind the epitympanic recess Connected to the recess by the aditus The lat SCC lies medial to the aditus Medial wall of the antrum is related to the post SCC Tegmen tympani forms the roof 29  About 1cm in diameter but varies When large it will be covered by thin layer of bone & when small is covered by thick layer 30  Pharyngotympanic tube Connects the nasopharynx with the middle ear Over 3cm long Has bony & cartilaginous parts 31 Bony parts Over 1cm long Tapers down from the ant wall of middle ear to the orifics Narrowest part ( isthmus) Lined with mucoperiostum Surface is ciliated columnar epithelium with no gland 32  Cartilaginous parts Over 2cm long Joins the bony part at the isthmus Made up of elastic carti Surface is ciliated columnar epithelium with mucous gland B/S – ascending pharyngeal & middle meningeal a V/D – into pharyngeal plexus 33  L/D – to retropharyngeal nodes N/S – pharyngeal branch of pterigopalatine ganglion(maxillary n) & tympanic plexus Function – ventilation of middle ear Transport of mucous from middle ear 34  Inner(internal)ear Consists of the bony labyrinth (BL) in the petrous temporal bone & the membranous labyrinth (ML) that lie within the bony labyrinth. Contains the organ of hearing - the cochlea. The organs of balance - the utricle, saccule & semicircular canals. 35  The gap blw the bony labyrinth & the membranous labyrinth is filled with perilymph. ML contains endolymph 36  OSSEOUS (BONY) LABYRINTH (BL) Is a series of cavities lined by endosteum. Opens into the medial wall of middle ear via – Oval window ( closed in life by footpiece of stape) – Round window (closed in life by secondary TM) – Aqueduct of vestibule(closed in life by endolymphatic duct) & aqueduct of cochlea through which perilymph drain into CSF 37 Consists of :  vestibule  semicircular canals  Cochlea Contains the membranous labyrinth The bone is denser & harder than that of the other parts of the petrous bone it is d/4 possible, particularly in young skulls, to dissect the bony labyrinth out from the petrous temporal bone. 38  Cochlea Conical snail-shaped cavity in the petrous bone Most anterior part of the labyrinth Lies in front of the vestibule. It is 5mm from base to apex & 9 mm across its base. Its apex, or cupula, points towards the anterosuperior area of the medial wall of the tympanic cavity It has a conical central bony core, the modiolus, & a spiral canal runs around it. 39  A delicate osseous spiral lamina (ledge) projects from the modiolus, partially dividing the canal Within this bony spiral lies the membranous cochlear duct The cochlear canal spirals for about 2¾ turns around the modiolus and is 35 mm long. 40  At its first turn, the canal bulges towards the tympanic cavity where it underlies the promontory. 3 mm in diameter at the base & reduces progressively as it spirals apically to end at the cupula. Openings at the base: round and oval windows, smaller opening for the cochlear aqueduct or canaliculus. 41  Vestibule Is a hollow in the petrous bone. Contains the membranous saccule & utricle The scala vestibule of the cochlea open into the front of the vestibule 5 openings of SCC opens posteriorly Medial wall is formed by IAM & Lat wall by middle ear 42  Semicircular canals Lie in 3 plane at right angle to each other Each is about 2/3 of the circle About 20mm each & 1mm in caliber except at ampulla(2mm) Anterior SCC Placed in a vertical plane across the long axis of the petrous bone Convexity outward & ampulla laterally 15-20mm 43  Posterior SCC Placed in a vertical plane across the long axis of the petrous bone Convexity backward & ampulla below 18-22mm Lateral SCC Placed 30 degrees off the horizontal plane Convexity backward & laterally Ampulla anteriorly 12-15mm 44  Membranous labyrinth (ML) Is a continuous system of ducts & sacs within the bony labyrinth Filled with endolymph Separated from the periosteun that cover the BL by perilymph Has 2 sacs(saccule & utricle), 4 ducts; 3SCC & cochlea 45  3 coverings Outer fibrous layer – vascular & adheres to the endosteum of BL forming stria vascularis that produce endolymph Intermediate layer – homogenous like basal lamina Inner epithelial layer – elaborated in 3 places into receptors of sound, static & kinetic balance 46 Cochlea duct The spiral anterior part of ML Contains sound receptors Attached to the apical surfaces of spiral lamina & outer bony wall of the cochlea Starts as blind extremity at the apex of the cochlea & ends in a bulbous extremity. Ductus reuniens connects the extremity with the saccule 47  2 membranes enclose the duct & it is triangular in cross section One side of the triangle is formed by basilar membrane which extends in line with spiral lamina to the outer bony wall Other side is formed by vestibular(Reissner’s) memb. 48 Organ of corti Consists of series of epithelial structure that lie on the zona acuata of basilar memb At the centre are 2 rows of cells(inner & outer) pillar cells Base of the cell rest on the basilar memb Blw the cells & basilar memb are the tunnel of corti Internal to the inner pillar cell is a single row of inner hair cell Ext to the outer pillar cell are 4 rows of outer hair cells The hair cells are receptors for hearing. 49  Organ of balance Saccule Fibrous sac that lies in the lower part of vestibule Connected to the basal part of the cochlea duct by ductus reuniens To the utricle & endolymphatic duct by utricosaccular duct The sensory receptor(macular) of saccule(2.6mm Long & 1.2mm wide) are found at the medial wall 50  Utricle Larger, irregular oblong dilated sac that occupy the posterosuperior region of the vestibule Receives the openings of SCD At the floor of the utricle is the macula & sensory receptor for static balance 51  SCD Corresponds to the SCC Open into the utricle A transverse crest on the medial surface of each ampulla forms the crista which contains the sensory receptor(hair cells) for kinetic balance 52  The hair cells of the macular of utricle & saccule & the cristea of SCD are stimulated by mvt of the otolithic memb or copular respectively in response to head mvt 53  Blood supply A. bony labyrinth Ant tympanic branch from maxillary a Stylomastoid branch from post auricular a Petrosal branch from middle meningeal a B. Memb labyrinth Labyrinthine artery - from ant inf cerebella a or direct from basillar a Divides into cochlea & vestibular branches 54  V/D – Via vestibulae & cochlea v, empties into inf petrosal or sigmoid sinuses N/S – Vestibulocochlear n 55 THANKS FOR LISTENING 56