Anatomy and physiology of ear

Human body

1. Topic: Anatomy and physiology of Ear

2. synopsis
Introduction.
Anatomy of ear.
Physiology of hearing.
Physiology of equilibrium.
Conclusion.
Reference.

3. INTRODUCTION
The ear is the organ of hearing and equilibriumthat detects and
analysis sound by the conversion of sound waves into electroch-
emicalimpulses.
The sensory receptors can have ability to transducesound vibra-
tionsinto electrical signals 1000 times faster than photorecepto-
rsthat can respond to light.
The auditory range extends from 20 to 20,000 hertz.
The sound intensity is measured in units called decibels(dB).

4. ANATOMY OF THE EAR
Ear is divided into three main regions
The External ear
consists of auricle, external auditory canal and ear drum.
Theauricleorpinnaisanelasticcartilagecoveredbyskin.
Theexternalauditorycanaliscurvedtubeabout2.5cmlong
thatliesinthetemporalboneandleadstoeardrum.
Theeardrumisathin,semitransparentpartitionbetween
externalauditorycanalandmiddleear.
Thetympanicmembraneiscoveredbyepidermisandlined
simplecuboidalepithelium.Betweenepitheliallayersis
connectivetissuecomposedofcollagenelasticfibresandfibro
blasts.

6. Middle ear
Themiddleearisairfilledcavitythatislinedbyepithelium
Middleearcontainsthreesmallossiclesmalleusincusandstapes,
•thatareattachedbyeachotherbyligamentsandareconnected
•bysynovialjoints
Thehandleofthemalleusattachestotheinternalsurfaceofthe
•tympanicmembrane,theincusattacheswiththeheadofthe
•stapesandthestapesfittesintoovalwindow
Besidestheligaments,thetwotinyskeletalmusclesalsoattaches
•toossicles,thetensortympanimuscleattachedtothemalleus
•andthestapediusattachetothestapes.
Theauditorytubeareeustachiantubewhichconnectsthemiddle
•earwiththenasopharynxwhichconsistsofboneandcartilage.

8. Internal ear
•The inner ear is also called the labyrinth because of its complicated
series of canals.
•Structurally consists of two main divisions, an outer bony labyrinth
and an inner membranous labyrinth.
•The inner membranous labyrinth is long tube like structure.
•The inner ear is divided into three parts, semicircular canals,
vestibule and cochlea.
•The vestibule is oval central portion of the labyrinth.
•The membranous labyrinth in the vestibule consists of two sacs
called utricle and the sacculeconnected by small duct.
•There are three semicircular canals, based on their position they
are called anterior, posterior and lateral. At one end of each canal is
swollen enlargement called ampula

9. Cont….
•Anterior of the vestibule is the cochlea a bony spiral canal that
resumblesa snail shells and makes almost three turn around a
central boneycore called modiolus.
•If we draw the section of cochlea reavelsthat it is divided into three
compartments, scalavestibuli, scalamedia and scalatympani.
•The scalatympani are separated with the scalamedia by vestibular
membrane.
•The basilar membrane separates cochlear duct and scalar tympani.
•The organ of cortiare present on the basilar membrane that contains
hair cells and supporting cells. Almost 16,000 hair cells are present in
the organ of corti.
•The vestibulocochlear(viii) nerve are attached with the inner ear by
two branches, vestibular branch and cochlear branch.

11. Physiology of hearing
•When the sound waves travels through the auditory canal hits the
tympanic membrane the tympanic membrane vibrates and send
them towards the middle ear where the ossiclesamplify sound
towards oval window.
•The oval window bulges inwards and round window moves outwards
due to fluid pressure wave.
•The pressure wave travels through scalavestibuli, then scalatympani
and then move in the cochlear duct.
•The pressure wave in the endolymphcauses the basilormembrane to
vibrate hair cells move against tectorialmembrane to generate nerve
impulses that finally reachresin the brain where it is interpreted.

12. Cont….
•Highpitchedsoundisabsorbedatthebaseofcochleabecause
ofstiffness.Lowpitchedsoundabsorbedattheapexregionof
thecochlea
•Louder sound also may stimulate large number of hair cells.
Therefore leads to higher action potential.
•The hair cells transducethe mechanical vibrations into
electrical signals.
•As the basilar membrane vibrates the hair cells bend back and
forth and slide one another.
•The tiplinkprotienconnects the tip of stereociliumto ion gated
channels called trandictionchannels.

13. Cont….
•As the stereociliaband in the direction of kinociliumthe tip link
tug on the transduction channels and open them.
•The channels allow the potassium and calcium ions enter in the
hair cells where the depolarization occurs.
•The calcium ion helps the synaptic vessicleto fuse with plasma
membrane leads to exocytosisof neurotransmitters (gultamate)
that stimulates afferent neurons in which action potential is
generated and ultimately reaches in the brain where the
impulse is interpreted.

16. Physiology of equilibrium
Utricle and Saccule
•These two structures are located in the vestibular portion of inner ear in
the membraneouslabyrinth.
•Basically outer bony labyrinth contain perilymphwhereas inner
membraneouslabyrinth contains endolymph.
•The utricle and sacculecontains special detectors called macula.
•The macula are the small thicknedregion.
•Macula are two in number one is present in utricle and one is present in
saccule.
•The macula of utricle is present on the floor whereas maculeof sacculeon
the wall.
•Maculae contains receptors for static equilibrium.
•The maculae detects linear acceleration but in the horizontal direction.
•The macula of sacculedetects the linear acceleration but in vertical
direction.

17. Cont...
•The macula of both utricle as well as sacculeconsists of two kinds
of cells.
•The hair cells as well as supporting cells. And also contains
vestibular dark cells.
•A gelatinous, glycoprotein layer called otolithicmembrane that rest
some hair cells.
•The otolithicmembrane sits on the top of the macula.
•The otolithicmembrane pushes the stereociliatowards the
kinociliumdue to which ion gated channels open and the Potassium
and Calcium cationsenter into the hair cells.
•The calcium ion attaches with the neurotransmitter vesicles and
helps to fuse the vesicle with the plasma membrane of hair cells.
•Which may leads to release of neurotransmitters that sends action
potential in the vestibular branch of 8
th
nerve that reaches in the
brain.

20. Semicircular canals
•They are responsible for dynamic equlibrium. They detects
rotational acceleration.
•The semicircular ducts contains special detectors that is called
cristaampularispresent in the ampula.
•Cristacontains a group of hair cells and supporting cells.
•The cupulaare present on the hair cells.
•As the head rotates in one direction, the cupulais dragged
through endolymphand bend in opposite direction.
•Bending of hair bundles produces receptor potentials. In turn
the receptor potentials leads to nerve implusesthat pass
along the vestibular branch of the vestibulocochlear(viii)
nerve.

21. Cont....
•The action potentials or impulses stimulates vestibular
nuclei that sends commands to nuclei of cranial verves
that controls coupled movement of eyes with those of
head.
•Nuclei of accessory nerves controls head and neck
movements and maintaining equilibrium.
•Vestibulospinaltract conveys impulses down the spinal
cord to maintain muscle tone in skeletal muscles to
help maintain equilibrium.
•Ventral posterior nucleousprovide us with conscious
awareness of position and movement of head and
limbs.

24. CONCLUSION
•The ear is the organ of hearing and equilibrium.
•The ear converts the mechanical energy into
electrical energy.
•The ear uses resonance, impedance and analysis.
•By understanding the physiology of hearing and
balance, we came to know that every organ in
our body is performing complex functions.

25. References:
•Anatomy and physiology by Gerard j. Tortora
•Internet