Describe, in general, the structures found in the external, middle, and inner ear.

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I. External ear - pinna (elastic cartilage) and external auditory meatus (stratified squamous epithelium) -- elastic cartilage (outer 1/3) -> temporal bone (inner 2/3rds)

(a) sebaceous glands, hair follicles, and ceruminous glands -- modified apocrine sweat glands that make ear wax (saturated fatty acids, sloughed keratinocytes, antimicrobial)

II. Tympanic membrane - eardrum, epithelial sheet

(a) outer side -> thin keratinized stratified squamous

(b) inner side -> simple cuboidal epithelium or squamous (continuous with lining of tympanic cavity)

(c) they cover a sheet of collagen, elastic fibers, and fibroblasts, which are reduced at the pars flaccida

III. Middle ear - an irregular space (tympanic cavity) within the termporal bone lined by cuboidal epithelium

(a) auditory tube - connects the middle ear with the pharynx and, when open, balances the air in the middle ear with atmospheric pressure

(b) mastoid air cells - located posteriorly

(c) auditory ossicles- malleus, incus, and stapes - "hammer", "anvil" and "stirrup" - connect the tympanic membrane to the oval window; malleus connects the tympanic membrane; stapes connects to the oval window -- on the medial wall

IV. Inner Ear - cavity within the bone

(a) bony labyrinth - houses a set of continuous fluid-filled epithelium lined tubes and chambers--membranous labyrinth

i. cochlea - contains the organ of Corti

ii. Saccule and utricle - static position, macula in these structures

iii. semicircular canals - angular movement is sensed by cristae ampullares within the ampulla; anterior, posterior; lateral semicircular canals

(b) CN VIII - vestibular and cochlear divisions

Define the following inner ear structures: bony labyrinth and its parts

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bony labyrinth - interconnected network of canals, lined by endosteum bearing mesenchymal squamous cells; contains perilymph

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Define the following inner ear structures: membranous labyrinth and its parts

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membranous labyrinth - lined by simple squamous epithelium, patches of sensory cells covered by jelly; contains endolymph

Divided into two major divisions:

vestibular labyrinth -sense of static position (equilibrium)

i. two connected sacs (utricle and saccule)

ii. 3 semicircular ducts

cochlear labyrinth - hearing, cochlear duct, which contains the organ of Corti

cochelar labyrinth

perilymph - similar in ionic composition to CSF and ECF of other tissues; contains little protein

drained by perilymphatic duct;

emerges from the microvasculature of the periosteum;

suspends and supports the closed membranous labyrinth, protecting it from the hard wall of the bony labyrinth

endolymph - contains high potassium, low sodium, and low protein

fills the membranous labyrinth

produced by capillaries in the stria vascularis in the wall of the cochlear duct

drained from the vestibule into venous sinuses of the dura mater by the small endolymphatic duct

Sensory areas of the membranous labyrinth include:

- Cristae ampullares (3):

- Maculla utriculi

- Macula sacculi

- Organ of Corti

The cristae ampullares and maculla have similar structures.

•Type I and Type II hair cells (large areas of columnar sensory mechanoreceptors) have synapses with afferent nerve endings and their afferents have efferent fibers which modify the sensitivity of the mechanoreceptors.

•Hair cells surrounded by supporting cells

•stereocilia - rigid unbranched microvilli arranged in increasing length as the kinocilium (basal body + microtubule doublets) is approached on the cell surface; embedded in otolithic membrane - a thick gelatinous layer of proteoglycans (only in macula)

Explain how the cristae ampullares differ from the maculae.

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I. Cristae ampullaris- ridgelike are of mechanoreceptors in the ampulla of the semicircular ducts; they have a "flapper valve"--the cupola

the microvilli and kinocilium of cristae amupllaris hair cells are embedded in the cupola -- proteoglycan layer --thicker and does not contain otoliths as opp. to the otolithic membrane of the macula

maculae - have a gelatinous layer with otiliths (otoconia), or calicified structures - otolithic membrane; bending of the cilia and microvilli generate action potentials; the otoliths help determine whether one is upside-down by means of gravity

kinocilium and microvilli embedded in the otolithic membrane

Describe the structure and function of each of the following: vestibular type I and type II cells

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Type I has a pear shape whereas Type II are cylindrical 

Type I has a cup shaped afferent nerve at base as well as efferent nerves; Type II has afferent and efferent nerves

Describe the structure and function of each of the following: cristae ampullares

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Describe the structure and function of each of the following: macular utriculi and sacculi

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macula utriculi and sacculi

Microvilli and kinocilium of hair cells embedded in the otolithic membrane

• The gel-like membrane contains otoliths

Gravity and linear acceleration cause movement of the membrane and hair cell depolarization

Describe the structure and function of the cochlea, including the following important components: inner and outer hair cells

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cochlea - A cone shaped coil making 2.75 turns around the modiolus; part of the membranous labyrinth connected to the saccule; highly specialized sound receptor; contains endolymph

Scala vestibuli and scala tympani contain perilymph
•Helicotrema- an opening where they communicate at the apex of the cochlea;

outer hair cells: 3-5 rows near the oval window -> apex of the cochlea.

inner hair cells: 1 row of inner hair cells closest to the spiral lamina;

these resemeble vestibular receptor cells; afferent and efferent nerve endings, stereocilia (microvilli), but only a basal body--no cilium; microvilli are buried in the gelatinous tectorial membrane; action potentials are generated when the microvilli are bent

Describe the structure and function of the cochlea, including the following important components: stria vascularis (STV)

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stria vascularis - a unique epithelium that has intraepithelial capillaries; located on the lateral wall of the cochlear duct; produces potassium-rich endolymph,

basal plasma membrane infolding (numerous mitochondria)

Describe the structure and function of the cochlea, including the following important components: tectorial membrane

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tectorial membrane - an acellular layer that overlies and contains the tips of the stereocilia of the outer hair cells of the organ of Corti

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Describe the structure and function of the cochlea, including the following important components: basilar membrane

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basilar membrane - thick basal lamina that supports the Organ of Corti

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Describe the structure and function of the cochlea, including the following important components: phalangeal cells

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phalangeal cells - supportive role and surround inner hair cells completely; they surround the basal ends of the outer hair cells, and have a process that runs apically and expands into a plate, which supports the apical region of the hair cell

form tight junctions between themselves and with hair cells at their apical ends; isolating the lumen of the cochlear duct with its potassium-rich endolymph from the spaces in the organ of Corti which are sodium-rich perilymph

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