Download Histology Ass. Lec. Dentistry College Lec-12

Histology
Lec-12-
Ass. Lec.
Wafaa H. M. Alhashimy
Dentistry College
Second Stage
Organ of special senses
Ear Histology
The ear , the organ of hearing and balance is composed of three regions : the outer
ear , the middle ear and the inner ear .
External ear: Composite of three region
*The auricle (pinna): is composite of an irregularly shaped plate of elastic cartilage
covered by thin skin.
* The external auditory meatus& canal : is the canal extended from the pinna to the
tympanic membrane. The external 1/3 of the external auditory meatus composite of
elastic cartilage covered by thin skin contain hair follicle, sebaceous glands, and
modified sweat glands called ceruminous glands, which produce wax material called
cerumen. The enternal 2/3 composite of temporal bone no thin skin.
*The tympanic membrane : composite of
1- External surface of the tympanic membrane is covered by simple sequamous
membrane derived from Ectoderm.
2- Middle layer of the tympanic membrane is including collagen , elastic fiber and
fibroblasts derived from mesoderm.
3- Inner surface of the tympanic membrane is covered by simple sequamous to
simple cuboidal derived from endoderm.
Middle ear (tympanic cavity )
The middle ear is the portion of the ear internal to tympanic membrane, and external
to the oval window of the cochlea. tympanic cavity ling by simple cuboidal epithelial
communicate with The eustachian tube, joins the tympanic cavity with the nasal cavity
(nasopharynx), allowing pressure to equalize between the middle ear and throat.
The middle ear contains of :
--three tiny bones known as the ossicles: malleus, incus, and stapes. The ossicles
directly couple sound energy from the ear drum (tympanic membrane) to the oval
window of the cochlea.
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--muscle.
malleus
Incus
stapes
Middle ear
The malleus attached with tympanic membrane . the stapes attached with oval window
on cochlea ,this window closed by the foot of stapes for transmit waves to perilymph
in cochlea.
The Eustachian tube contains
1-Posterior 1/3 composite of bony that covered with simple columnar ciliated
epithelium .
2-Anterior 2/3 composit of : cartilage that covered by seudositratified epithelium.
Inner ear
Is composed of the bony labyrinth and the membranous labyrinth .
The Inner ear consists of:
A- Auditory system: Cochlear labyrinth for hearing.
B- Vestibular system: Vestibular labyrinth , is responsible for the sensations of
balance and motion which consist of:
1. The vestibule:
2. The semicircular canals.
The vestibule:
It is containing the utricle and saccule of the membranous labyrinth. contain a hair
cells and supporting cells called a macula. Each hair cell of a macula has 40-70
stereocilia and one true cilium called a kinocilium. The tips of these cilia are
embedded in a otolithic membrane.
semicircular canals : composit of three bony and three membrane semicircular canals
(superior, posterior and lateral) . Each canal is filled with endolymph fluid. At the
base of each canal enlarged which opens into the utricle and has sac at one end called
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ampullae. In the ampulla is a mound of hair cells and supporting cells called crista
ampullaris. These hair cells have many cytoplasmic projections on the apical surface
called stereocilia which are embedded in a gelatinous structure called the cupula.
Cochlea
The cochlea, dedicated to hearing; converting sound pressure patterns from the outer
ear into electrochemical impulses which are passed on to the brain via the auditory
nerve.
As has stated the cochlea is a bony cavity, and this cavity is divided from the inside to
the three floors.
-The upper called scala vestibuli, contain liquid known Perilymph
-basement called the scala tympanic, contain liquid known Perilymph
-In the East called cochlear Duct, contain liquid known endolymph
And separates the scala vestibuli and cochlear Duct the vestibular membrane.
While membrane separates (Basilar Membrane) between the cochlear Duct and the
scala tympanic.
And there are oval Window at the beginning of the scala vestibuli, while the Round
Window located at the end of the scala tympanic .
The Round Window closed by elastic membrane for yields to increased pressure in
internal ear.
Organ of Corti
1. The organ of Corti rests on the basilar membrane , overlays the stereocilia
of inner and outer hair cells. These are the sensory cells of the inner ear.
2. The tunnel of Corti (inner tunnel) is flanked on either side by the inner and
outer pillar cells.
3. There are 3 rows of outer hair cells and a single row of inner hair cells
adjacent to the inner.
4. As sound waves travel, they distort the vestibular membrane and the basilar
membrane of the organ of Corti, which, in turn, causes movement of the hair cells in
contact with the tectorial membrane. This mechanical stimulation of the hair cells is
transferred to the dendrites of the spiral ganglion cells.
Not : the converting sound pressure patterns from the outer ear into mechanical
vibration in meddle ear and finally converted into electrochemical impulses which are
passed on to the brain via the auditory nerve.
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