Dow University of Health sciencesInstitute of Nursing

Anatomy of Ear

By: Maghan DasBscN student

16th July,2014

Maghan Das

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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Anatomy of Ear

Ear is divided into three main regions External ear Middle ear Inner ear

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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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Auricle

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External auditory canal

Curved tube 2.5cm longIt is a thin, semitransparent partition between external

auditory canal and middle ear.It is covered by epidermisLined by simple cuboidal epithelium It lies in temporal bone and leads from auricle to ear drum

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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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Maghan Das

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 OssiclesOval window Eustachian tube

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Tympanic membrane

It is pearly gray This is a three-layered structure

Outer layer is skinConnective 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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Conti…This ends at a point known as the umboThe anterior and posterior malleolar folds divide the

tympanic membrane into two distinct parts: Upper pars flaccida Lower pars tensa.

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Auditory OssiclesThese are the smallest three bones of the body Connected by synovial joints

Malleus = Hammer Incus Stapes

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MalleusWord malleus is Latin for hammerIt is the first bone of the middle earThe 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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Malleus

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Incus (Anvil)

It is second bone Articulates with head of stapes located in between the malleus and the stapesThe incus transmits vibrations from the malleus to the stapes

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Incus

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Stapes Stapes is the third and final bone of the middle earIt is the smallest and lightest bone of the human bodyThe 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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Eustachian TubeThe middle ear is an air-filled spaceIt 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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Eustachian Tube

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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 tubeThe 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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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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Middle Ear muscles

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Inner Ear It is also called as labyrinth Two main divisions of labyrinth

Outer Bony labyrinthInner membranous labyrinth

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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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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 signalsVestibule It is oval central portion of bonylibrinth Membranous labyrinth consists of two sacs.

Utricle Saccule

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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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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 AmpulaOne end of each canal is swollen enlargement is called ampula

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Cochlea Snail shaped Bony spiral canal Divided into three channels

Cochlear duct Scala vestibuli Scala tampani

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Labyrinth

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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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Physiology of Hearing 1. Auricle directs sound waves into external auditory

canal2. 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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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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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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Thank youMaghan Das