1. The ear (L2)
2012

2. EXTERNAL EAR
Auricle (pinna)
Externa auditory
Tympanic membrane

3. 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 …….

4. 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

5. 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

6. Middle ear

7. 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

8. Middle ear (Eustachian tube)

9. 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

10. 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

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

12. 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

13. 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

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

16. 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

18. 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

19. C B A B

20. 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

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

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

23. 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

24. Cristae ampullaris in semicircular duct

25. 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