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The ear (L2)

2012

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EXTERNAL EAR

Auricle (pinna) Externa auditory Tympanic membrane

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1. Auricle

• Irregular elastic cartilage plate • Connective tissue • Thin skin, fine hair with sebaceous and sweat glands

2. (Externa auditory) External auditory canal

• Lined by thin skin • Elastic cartilage continuous with auricle • Replaced with bone deeper in canal• Lateral 1/3 modified sweat glands with large lumens • Subcutaneous connective tissue fused with perichondrium

3. Tympanic membrane …….

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3. Tympanic membrane • Thin membrane separates external ear from middle ear • Small area superiorly pars flaccida, rest tense pars tensa• Attached to surrounding bone by a fibrocartilaginous ring

Cellular structure of tympanic membraneExternal cuticular layer

Fine hair, glandless skin and dermis that is finely vascular

Fibrous layerOuter layer fibers radiating from center to circumference Inner layer, circular arrangement at periphery

Inner mucous layerSingle layer cuboidal cells, lamina propria with blood vessels

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Middle ear Air filled cavity Sound waves hit the tympanic membrane Transmitted by ossicles (malleus, incus, stapes)

Malleus attached to tympanic membrane Incus joins the two bones Stapes fits into the oval window

Then transmitted to fluid filled inner ear Middle ear joins anteriorly to nasophyrynx by auditory tube

(Eustachian tube) Joins inner ear through medial oval (vestibular) and round

(cochlear) windows

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Middle ear

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• Middle ear and mastoid cavities line with simple squamous or cuboidal epithelium

• malleus, incus and stapes: synovial joints • Lamina propria is fused with the periosteum

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Middle ear (Eustachian tube)

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2. Auditory tube (Eustachian tube)

Equalizes pressure Slit-shaped Ciliated pseudostratified columnar epithelium Incomplete cartilage ring J-shaped Cartilage is partly hyaline and partly elastic Lamina propria of cartilaginous section contains mixed glands

+ lymph follicles

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Internal ear consists of cavities and canals located in the

pars petrosa of the temporal bone Consists of two labyrinth compartments, “one inside the other” Bony labyrinth =consists of cavities and canals located in the

pars petrosa of the temporal bone =perilymph Membraneous labyrinth = lies within the bony labyrinth and

consists of sacs and tubules =endolymph Perilymph = similar ionic composition as extracellular fluids but

has a low protein content Endolymph = low sodium and high potassium content, low

protein

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Bony labyrinth: Located in the pars petrosa of the temporal bone

Membraneous labyrinth:Located within the bony

labyrinth and consists of sacs and tubules

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Oval window from middle ear leads to the = vestibule

Cochlea = anterior

3 Semicircular canals =posterior

Ampullae = 5 openings in posterior vestibule wall

Lining = squamous epithelium on a thin lamina propria fused to periosteum

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Vestibule two membranous sacsAnterior saccule, posterior utricule Joined by two short legs of Y shaped tube =endolymphatic duct Extends through pars petrosa and terminates as a dilated sac Surrounded by connective tissue and blood vessels

Membranous labyrinth

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Functional components

Can divide the inner ear into two functional components1. Cohlear labyrinth –hearing=Organ of Corti2. Vestibular labyrinth – balance = cristae ampullaris +

maculae

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Cochlea labyrinth Spiral like a sea shell Contains the auditory sense organ Bony central part =modiolus Each turn 3 compartments Central = scala media (SM) (endolymph) Top= scala vestibuli (SV) (perilymph) Bottom =scala tympani (ST) Vestibular (Resseners membrane) =separates SM & SV Basilar membrane =separates SM & ST Outer wall of SM = stria vasularis (vascular) Outer wall of the ST = spiral ligament

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Spiral organ of Corti• On the basilar membrane the organ of Corti• Converts of sound waves into nerve impulses • Highly specialized region

Two basic types of cells• Sensory cells (hair cells) + Support cells

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A BB

C

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Central (A), tunnel of Corti created by inner/outer pillar cells Phalangeal cells supports a row of sensory (hair) cells (either

inner or outer) (B) Hair cells have long microvilli Microvilli are embedded in the surface of the tectorial

membrane (gelatinous matrix containing thin keratinous fibers) (C)

5 rows outer hair cells Deiter’s cells or outer phalangeal cells + Hensen’s cells +

Claudius cells +Boettcher’s cells

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Innervationinner hair cells are mechanoreceptors

outer hair cells register sound waves

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2. Vestibule labyrinthUtricule, saccule and the semicircular canals

Thin walls with rich vascular connective tissue Layer of squamous or cuboidal epithelium Connective tissue

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Cristae ampullaris

Sensory receptor for angular movementFound in semicircular ductEpithelial ridge consisting of epithelial hair and supporting cellsCupula (dome) = gelatinous protein polysaccharide massSurrounded by endolymphMovement of cilia generates nerve impulses

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Cristae ampullaris in semicircular duct

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Maculae of the saccule and utricle

Innervated thickenings of the epithelium Hair cells contain microvilli, enbedded embedded in gelatinous

membrane = otolithic membrane On the upper surface of the otolithic membrane are CaCO3

crystals= otoliths of statoconia Beneath hair and supporting cells the connective tissue of

utricule, saccule and semicircular canals is thickened fused with the periosteum When gelatinous membrane moves, the microvilli move and

causes the initiation of nerve impulses

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