Download Histology Lecture 25 The Ear

In the name of God
The Ear
Dr. Zahiri
The Ear
• is responsible of hearing and balance
•This organ is composed of three regions, external ear, middle ear,
and inner ear
•External ear received sound and translated sound into mechanical
vibrations
•Middle ear amplified mechanical vibrations
•Inner ear regulate hearing and maintain equilibrium
•Vestibulocochlear nerve transmits sensory signals to the brain
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Dr. Maria Zahiri
External Ear
•The external ear is composed of :
the auricle or pinna
external auditory meatus
tympanic membrane
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•The auricle is composed of a plate of elastic cartilage covered by
thin skin
•The initial segment of external auditory meatus is composed of
elastic cartilage that is continuous with the cartilage of pinna
•Inner 2/3 of meatus is composed of bone
•External auditory meatus
is covered with thin skin
containing hair, sebaceous
glands and modified sweat
glands known as ceruminous
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glands
secrete earwax
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Cerumen
• A mixture of relatively
viscous secretions from the
sebaceous glands and nonviscous secretion from the
ceruminous glands (modified
apocrine glands)
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•Tympanic membrane covers the deepest end of the external
auditory meatus
•External surface of tympanic membrane is covered by a thin
epidermis
•internal surface is lined by a simple squamous or low cuboidal
epithelium
•The core of membrane is composed of a thin layer of connective
tissue elements
Dr. Maria Zahiri
Dr. Maria Zahiri
•Middle Ear
•The tympanic cavity which is an air filled space in temporal bone is
covered by simple squamous or low cuboidal epithelium
•Three auditory ossicles located here are composed of compact bone
•The ossicles covered by simple squamous epithelium and articulate
together by synovial joints
•Two skeletal muscles control motion between bone
•Auditory (Eustachian) tube is lined by pseudostratified columnar
ciliated epithelium
Dr. Maria Zahiri
Dr. Maria Zahiri
Eustachian (Auditory) Tube
• Wall is bone closest to tympanic cavity, replaced by elastic cartilage
except in nasopharynx where it becomes hyaline cartilage
• Lined with ciliated epithelium, goblet cells and diffuse lymphoid
tissue.
• Equalizes air pressure between the tympanic cavity and the external
environment. Walls normally closely apposed but open during
swallowing and yawning.
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•Inner Ear
•Inner ear is composed of bony labyrinth and membranous labyrinth
•Bony Labyrinth
•is part of temporal bone that is lined by endosteum
•Perilymphatic space separated bony labyrinth from membranous
labyrinth which is filled by a clear fluid known as perilymph
•Membranous labyrinth suspended in this fluid
•Central region of bony labyrinth is called vestibule that is
between posteriorly placed semicircular canals and anteriorly placed
cochlea
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INNER EAR –
A membranous labyrinth
filled with endolymph
inside a bony labyrinth filled
with perilymph
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Bony Labyrinth
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Components of the Bony Labyrinth
1. Vestibule: Contains Utricle and Saccule
2. Semicircular Canals: Extend from vestibule. Superior,
lateral and posterior at right angles to one another.
Contains the semicircular ducts. At one end of each is a
dilatation, the ampulla.
3. Cochlea: Coils like a snail around a central pillar of bone,
the modiolus.
The cochlear duct rests upon a partial shelf of bone projecting
from the modiolus, the osseous spiral lamina
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Helicotrema
Modiolus
Osseous
Spiral
Lamina
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Membranous Labyrinth
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Sensory Regions
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•Saccule and Utricle
•Saccule and Utricle are composed of a thin vascular CT that its inner
side is lined by a simple squamous to low cuboidal epithelium consists
of light and dark cells
•Light cells may play a role in absorption of endolymph and dark cells
control its composition
•Macula is a thickened specialized region of epithelium which acts as
receptor for linear acceleration
•Maculae are composed of neuroepithelial cells (type I) and hair cells
(type II) and supporting cells
•Type I and II cells have a single kinocillium and about 100 stereocilia
•Saccule and Utricle
•Stereocilia arranged in rows according to length, the longest being
nearest to kinocilium
•Supporting cells maintain the hair cells and contribute to
production of endolymph
•Stereocilia of neuroepithelial cells are embeded in a thick
gelatinous, glycoprotein membrane known as otolithic membrane
•Surface of this membrane is contains calcium carbonate crystals
known as otoliths or otoconia
• Type I and II cells innervated by vestibular branch of VIII
cranial nerve
Type I: Large cup-shaped ending
Type II: Many afferent endings
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Saccule & Utricle
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•Semicircular ducts
•These are located in semicircular canal, arising from utricle
•Near the utricle ducts expanded and form ampullae which are contain
cristae ampullares
•Crista ampullaris is composed of a ridge that covered by sensory
epithelium consists of supporting cells and neuroepithelial hair cells (
type I and II )
•Hair cells do not lie on basal lamina and are located between supporting
cells
•Cupula is similar to otolithic membrane but it is cone shape and has not
otolith
•Cochlear Duct
Cochlear duct contains organ of Corti that is responsible to responds to
sound
•
Modiolus has a lateral projection which is known as osseous spiral
lamina
•
Periosteum of the osseous spiral lamina forms spiral limbus
•
Spiral organ of Corti supported by the thickened periosteum of the
cochlea that is called spiral ligament
•
Basilar membrane is a thin membrane that extends between the spiral
ligament and the osseous spiral lamina
•
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Dr. Maria Zahiri
•Basilar membrane support the organ of Corti and its vibration induced
by disturbances in the perilymph detected by hair cells of the organ of
Corti
•Vestibular membrane extends across the cochlear duct
•Vestibular Membrane is composed of two layers of flattened
squamous epithelial cells
•Stria vascularis is a pseudostratified epithelium that contains
intraepithelial plexus of capillaries
•Stria vascularis extends between vestibular membrane and the spiral
prominence
•Spiral prominence is a protuberance covered by epithelium that
continuous with stria vascularis and continues onto basilar membrane
that is called cells of Claudius
COCHLEA DUCT
Scala Media is the space within the
triangular shaped cochlear duct. It is
filled with endolymph
The cochlear duct and the spiral lamina
divide the cochlea into two additional
spaces:
The scala vestibuli and the scala
tympani. Both are filled with perilymph
and are contiuous with one another at
the helicotrema
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•Cells of Organ of Corti
•It is composed of inner and outer hair cells and supporting cells
•Supporting cells consist of: inner and outer pillar cells, inner and outer
phalangeal cells and cells of Hensen
•Inner hair cells are neuroepithelial and responsible in the reception of
sound
•They are arranged in a single row along the entire length of cochlea
•Their stiff stereocilia arranged in a W-shaped formation but no
kinocilium
•At the base of each hair cell are efferent and afferent nerve endings that
transmit impulses to the bipolar neurons of the spiral ganglion.
Cochlear Duct
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•Cells of Organ of Corti
•Outer hair cells are also neuroepithelial are three or more rows
located between outer phalangeal and outer pillar cells
•Inner and outer pillar cells rest on basilar membrane, enclose the
inner tunnel of Corti
•Inner and outer phalangeal cells are intimately associated with the
inner and outer hair cells respectively
•They support nerve fibers that synapses with the hair cells
•Tectorial Membrane
•Tectorial membrane overlies the tip of hair cells
•It is composed of glycoproteins
Endolypmphatic Duct and Sac
• Simple squamous epithelial lining becoming columnar near the sac.
• Columnar epithelium has two cell types, one with microvilli,
pinocytotic vesicles and vacuoles.
• This cells may be responsible for the absorption of endolymph and
endocytosis of foreign materials
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Path of sound waves – in through oval window – up scala vestibuli – through
Helicotrema – along tympani and dissipation through round window
Dr. Maria Zahiri
Dr. Maria Zahiri
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