A) Define and Use Properly the Following Words: Ear, Tympanic Membrane (Eardrum), Middle

35.0 THE EAR

a)  Define and use properly the following words: Ear, Tympanic membrane (eardrum), Middle Ear, Ossicles (ear bones), malleus , incus, stapes, Auditory (Eustachian) tube, Inner Ear, membranous labyrinth, bony labyrinth, perilymph, endolymph, Cochlear, Equilibrium, semicircular canals, utricle, saccule, Vestibular Apparatus, Ampulla, neuroepithelium, sensory hair cells, long microvilli, single kinocilium, otoliths, sustentacular, crista, cupula, utricle, endolymphatic duct, Cochlear duct, modiolus, scala vestibuli, scala media, scala tympani, Vestibular membrane, Organ of Corti, Outer Hair cells, support cells, Tectorial membrane.

b)  Describe and associate basic structure/function for the following: all structures listed above; hearing and balance.

c)  Identify by microscopy: Ear, Tympanic membrane (eardrum), Middle Ear, Ossicles (ear bones), malleus, incus, stapes, Auditory (Eustachian) tube, Inner Ear, membranous labyrinth, bony labyrinth, perilymph, endolymph, Cochlear, semicircular canals, utricle, saccule, Vestibular Apparatus, Ampulla, neuroepithelium, sensory hair cells, long microvilli, single kinocilium, otoliths, crista, cupula, utricle, endolymphatic duct, modiolus, scala vestibuli, scala media, scala tympani, Vestibular membrane, Organ of Corti, Outer Hair cells, support cells, Tectorial membrane.

THE EAR

I. External Ear

1.  A funnel shaped opening

2.  Basic Components

a.  Elastic cartilage

b.  thin skin with hair, oil and sweat glands

c.  skeletal muscles

3.  Tympanic membrane (eardrum)

a.  Separates the external ear from the middle ear

b.  Outer surface covered by thin skin; CT between surfaces

c.  Inner surface covered by simple squamous epithelium continuous with tympanic cavity

d.  larger than the footplate of the stapes; thus, magnifies sound wave energy 22 times

II. Middle Ear

1.  Contains three ossicles, their muscles and ligaments

2.  Ossicles (ear bones)

a.  malleus

i.  hammer shape

ii. attached to the tympanic membrane and to the tensor tympani muscle tendon

iii.  articulates with the incus and temporal bone

b.  incus

i.  anvil

ii. articulates with the stapes

c.  stapes

i.  foot is fixed by the footplate in the oval window or the inner ear

ii. secured by the annular ligament

iii.  separated by a thin connective tissue from the inner ear fluid (perilymph)

3.  Auditory (Eustachian) tube

a.  connects tympanic cavity to the nasopharynx

b.  epithelium consists of pseudostratified ciliated columnar cells

c.  no glands in the osseous portion; but seromucous glands and lymphatic nodules in the cartilaginous portion

d.  elastic fibers near the pharynx

e.  In the HORSE

i.  auditory tube expands ventrally forming the guttural pouch

III. Inner Ear

1.  General information

a.  continuous system of fluid-filled sensory tubes and sacs called membranous labyrinth

b.  the bony labyrinth is external to the membranous labyrinth

c.  perilymph fills the space between the chambers

d.  endolymph fills the membranous labyrinth (high in K+)

e.  Membranous Labyrinth has two sensory components

i.  Cochlear deals with hearing

ii. Equilibrium

1.  semicircular canals

2.  utricle and saccule

a.  simple squamous epithelium, except for areas with neuroepithelium (sensory hair cells)

2.  Vestibular Apparatus

a.  bony vestibule filled with perilymph

b.  semicircular canals (3)

i.  ampulla contains sense organ with neuroepithelium on thick connective tissue

ii. sensory hair cells with long microvilli on apical surface with single adjacent kinocilium and the basal area extends through the basement membrane to synapse with efferent nerves

iii.  hen microvilli bend toward kinocilium, the cells increases its firing rate

iv.  embedded in layer of proteinaceous, gelatinous material with calcium carbonate crystals called otoliths

v. sustentacular cells, synthesize the matrix

vi.  crista is a ridge or crest found in the ampulla, which moves like a hinge; has hair sensory and support cells that are capped by the cupula (matrix without otoliths)

c.  utricle (each canal opens into), leads into the endolymphatic duct

3.  Cochlear duct

a.  Conical cochlea

i.  found within the anterior portion of the bony labyrinth

ii. appears like a snail’s shell

iii.  modiolus

1.  spongy bone shelf or axis through the canal

2.  base forms the cranial part of the internal acoustic meatus where the cochlear nerve and blood vessels enter the cochlea

b.  divided into three spaces:

i.  scala vestibuli (above)

ii. scala media (triangular shaped scala media splits the osseous cochlea)

iii.  scala tympani (below)

c.  Vestibular membrane (2 layers of squamous epithelium with tight junctions) separates scala media (cochlear duct) from the scala vestibuli

d.  Organ of Corti

i.  epithelial organ for hearing

ii. Neuroepithelium

1.  Columnar inner and outer Sensory Hair cells rest on support cell recesses

2.  W-shaped Outer Hair cells formed by long non-motile cilia

3.  support cells rest on a thick layer of ground substance (basilar membrane)

iii.  Tectorial membrane is formed by a glycoprotein-rich secretion that embeds the inner hair cells

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