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Anatomy and physiology of ear by maghan das
1. Dow University of HealtH sciences
institUte of nUrsing
Anatomy of Ear
By: Maghan Das
BscN student
16th
July,2014
Maghan Das
2. By the end of this lecture the students will be able to:
List the parts of ear.
Discuss the anatomy of ear
Understand the physiology of hearing
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3. Anatomy of Ear
Ear is divided into three main regions
External ear
Middle ear
Inner ear
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4.
5. External ear (outer ear)
External ear is consist of:
Auricle (pinna)
External auditory canal
Tympanic membrane (Ear drum)
Auricle
It is flap of elastic cartilage
It is covered by skin
Rim of auricle is called helix
Inferior portion is called lobule
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7. External auditory canal
Curved tube
2.5cm long
It is a thin, semitransparent partition between external
auditory canal and middle ear.
It is covered by epidermis
Lined by simple cuboidal epithelium
It lies in temporal bone and leads from auricle to ear drum
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8. Conti…..
Between the epithelial layer is connective tissue layer
Connective tissue layer is composed of collagen, elastic
fibers and fibroblast
Near the external opening the external auditory canal
contains a few hairs and ceruminous glands.
Ceruminous glands secrete the cerumen (ear wax)
Combination of hairs and cerumen helps prevent dust and
foreign objects from entering the ear
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10. Middle ear
Middle ear is small, air filled cavity in temporal bone
It is lined by epithelium
It is separated from external ear by ear drum
It separated from inner ear by oval window
The structures of middle ear are:
Tympanic membrane
Ossicles
Oval window
Eustachian tube
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11. Tympanic membrane
It is pearly gray
This is a three-layered structure
Outer layer is skin
Connective tissue
Inner layer is respiratory epithelium
A part of the first of the ossicles, the long process of
the malleus, is embedded in the lower part of the
tympanic membrane
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12. Conti…
This ends at a point known as the umbo
The anterior and posterior malleolar folds divide the
tympanic membrane into two distinct parts:
Upper pars flaccida
Lower pars tensa.
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15. Auditory Ossicles
These are the smallest three bones of the body
Connected by synovial joints
Malleus = Hammer
Incus
Stapes
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16. Malleus
Word malleus is Latin for hammer
It is the first bone of the middle ear
The handle of malleus is attached with internal
surface of eardrum
Head of malleus is attached with body of incus.
The primary function of the malleus is the
transmission of sound waves or vibrations from the
eardrum to the incus
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18. Incus (Anvil)
It is second bone
Articulates with head of stapes
located in between the malleus and the stapes
The incus transmits vibrations from the malleus to the stapes
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20. Stapes
Stapes is the third and final bone of the middle ear
It is the smallest and lightest bone of the human body
The stapes connects to the incus on the outward side
and to the oval window on the inward side.
The primary function of the stapes is transmitting
sound waves from the incus to the membrane of the
inner ear.
The base or footplate of stapes is fits into oval
window
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22. Eustachian Tube
The middle ear is an air-filled space
It consists of both bone and hyaline cartilage
This runs from the middle ear to the naso-pharynx
behind the nose.
It is normally closed at pharyngeal end
During swallowing and yawing it opens
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24. Middle ear muscles
There are two muscles in the middle ear:
Tensor tympani muscle
Stapedius muscle
Tensor tympani muscle
The tensor tympani runs in a canal along the roof of
the Eustachian tube
The tendon attaches to the handle of the malleus.
The muscle is supplied by a branch of the mandibular
branch of the trigeminal (fifth cranial) nerve
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25. Stapedius muscle
The stapedius is the smallest skeleton muscle in the
body
Nerve supply by branch of the facial (seventh cranial)
Attach with stapes
Contractions are reflex, initiated by loud sounds, and
when it contracts it pulls the stapes posteriorly, so
tilting its footplate
limits the potential damage caused by loud noise
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27. Inner Ear
It is also called as labyrinth
Two main divisions of labyrinth
Outer Bony labyrinth
Inner membranous labyrinth
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28. Outer Bony labyrinth
Bony labyrinth is a series of cavities in the temporal
bone
It is divided into three regions
Semicircular canals
Vestibule
Cochlea
Bony labyrinth is lined with periosteum and contains
perilymph
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29. Inner membranous labyrinth
It is series of sacs and tubes inside of bony labyrinth
membranous labyrinth is lined with epithelium
It contains endolymph
The level of potassium ions are high in endolymph
Potassium ions generates the of auditory signals
Vestibule
It is oval central portion of bonylibrinth
Membranous labyrinth consists of two sacs.
Utricle
Saccule Maghan Das
30. Saccule and Utricle
The walls of both Saccule and Utricle contain small
thickened region is called macula.
Pleural maculae
Contains receptor for static equilibrium
Maintains poster and balance
Maculae contains two type of cells
Hair cells
Supporting cells
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31. Semicircular canals
They are named:
Anterior Semicircular canals
Posterior Semicircular canals
Lateral Semicircular canals
Anterior and posterior are vertically oriented
lateral is horizontally oriented
Contains criste, site of hair cells, maintain static equilibrium
Ampula
One end of each canal is swollen enlargement is called ampula
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36. Organ of Corti
It is also known as spiral organ
Coiled sheet of epithelial cells
Supporting cells
Hair cells
Two groups of hair cells
Inner hair cells
Outer cells
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37. Physiology of Hearing
1. Auricle directs sound waves into external auditory
canal
2. When sound waves strike eardrum that cause
eardrum to vibrate
3. The central area of Ear drum is connected to malleus
which starts to vibrate. The vibration is transmitted
from malleus to incus then to stapes
4. As a stapes moves back and forth it pushes the
membrane of oval window in and out
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38. Conti….
5. The movements of the oval window sets up fluid
pressure waves in the perilymph.
6. The oval window bulges inward it pushes on
perilymph of scala vestibuli.
7. The pressure waves transmitted from scala vestibuli
to scala tempani
8. As a pressure deform the walls of scala vestibuli to
scala tempani, they push the vestibular membrane
back and forth creating the pressure waves in the
endolymph inside the cochlear duct.
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39. conti……
8. The pressure waves in endolymph cause basilar
membrane to vibrate, which moves hair cells in the
spiral organ against the tectorial membrane.
9. Bending of hair cells stereocilia produces receptor
potential that lead to generation of nerve impulses.
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