The ear (L2) 2012

EXTERNAL EAR Auricle (pinna) Externa auditory Tympanic membrane

2. (Externa auditory) External auditory canal 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 …….

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 membrane External cuticular layer Fine hair, glandless skin and dermis that is finely vascular Fibrous layer Outer layer fibers radiating from center to circumference Inner layer, circular arrangement at periphery Inner mucous layer Single layer cuboidal cells, lamina propria with blood vessels

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

Middle ear

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

Middle ear (Eustachian tube)

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

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

Bony labyrinth: Located in the pars petrosa of the temporal bone Membraneous labyrinth: Located within the bony labyrinth and consists of sacs and tubules

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

Vestibule two membranous sacs Anterior 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

Functional components Can divide the inner ear into two functional components Cohlear labyrinth –hearing=Organ of Corti Vestibular labyrinth – balance = cristae ampullaris + maculae

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

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

C B A B

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

Innervation inner hair cells are mechanoreceptors outer hair cells register sound waves

2. Vestibule labyrinth Utricule, saccule and the semicircular canals Thin walls with rich vascular connective tissue Layer of squamous or cuboidal epithelium Connective tissue

Cristae ampullaris Sensory receptor for angular movement Found in semicircular duct Epithelial ridge consisting of epithelial hair and supporting cells Cupula (dome) = gelatinous protein polysaccharide mass Surrounded by endolymph Movement of cilia generates nerve impulses

Cristae ampullaris in semicircular duct

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