Ear functions

Ear anatomy and funtions

1. ANATOMY OF
EAR
By :
Dr Manjula Vastrad
Asst Prof
Dept of Rachana Shareera
SMVVS RKM AMC
VIJAYAPUR

4. INTRODUCTION
Theearistheorganofhearingandbalance.
theearishavingthreeparts—
theouterear,
themiddleearand
theinnerear.

6. OUTER EAR
Theouterearistheexternalportionoftheearandincludesthe
fleshyvisiblepinna(alsocalledtheauricle),theearcanal,andthe
outerlayeroftheeardrum(alsocalledthetympanicmembrane).
Thepinnaconsistsofthecurvingouterrimcalledthehelix,the
innercurvedrimcalledtheantihelix,andopensintotheearcanal.
Thetragusprotrudesandpartiallyobscurestheearcanal,as
doesthefacingantitragus.Thehollowregioninfrontoftheear
canaliscalledtheconcha.Theearcanalstretchesforabout
1inch.Thefirstpartofthecanalissurroundedbycartilage,while
thesecondpartneartheeardrumissurroundedbybone.This
bonypartisknownastheauditorybullaandisformedby
thetympanicpartofthetemporalbone.Theskinsurroundingthe
earcanalcontainsceruminousandsebaceousglandsthat
produceprotectiveearwax.Theearcanalendsattheexternal
surfaceoftheeardrum.

8. MIDDLE EAR :
Themiddleearliesbetweentheouterearandtheinnerear.It
consistsofanair-filledcavitycalledthetympaniccavityand
includesthethreeossiclesandtheirattachingligaments;
theauditorytube;andtheroundandovalwindows.The
ossiclesarethreesmallbonesthatfunctiontogetherto
receive,amplify,andtransmitthesoundfromtheeardrumto
the inner ear. The ossicles are
themalleus(hammer),incus(anvil),andthestapes(stirrup).
Thestapesisthesmallestnamedboneinthebody.The
middleearalsoconnectstotheupperthroatat
thenasopharynxviathepharyngealopeningofthe
Eustachiantube.

9. Thethreeossiclestransmitsoundfromtheouterear
totheinnerear.Themalleusreceivesvibrations
fromsoundpressureontheeardrum,whereitis
connectedatitslongestpart(themanubriumor
handle)byaligament.Ittransmitsvibrationstothe
incus,whichinturntransmitsthevibrationstothe
smallstapesbone.Thewidebaseofthestapes
restsontheovalwindow.Asthestapesvibrates,
vibrationsaretransmittedthroughtheovalwindow,
causingmovementoffluidwithinthecochlea.

11. INTERNAL EAR :
Theinnerearsitswithinthetemporalboneina
complexcavitycalledthebonylabyrinth.Acentral
areaknownasthevestibulecontainstwosmallfluid-
filledrecesses,theutricleandsaccule.These
connecttothesemicircularcanalsandthecochlea.
Therearethreesemicircularcanalsangledatright
anglestoeachotherwhichareresponsiblefor
dynamicbalance.Thecochleaisaspiralshell-
shapedorganresponsibleforthesenseofhearing.
Thesestructurestogethercreatethemembranous
labyrinth.

12. Thebonylabyrinthreferstothebonycompartmentwhich
containsthemembranouslabyrinth,containedwithinthe
temporalbone.Theinnerearstructurallybeginsattheoval
window,whichreceivesvibrationsfromtheincusofthe
middleear.Vibrationsaretransmittedintotheinnerearintoa
fluidcalledendolymph,whichfillsthemembranouslabyrinth.
Theendolymphissituatedintwovestibules,
theutricleandsaccule,andeventuallytransmitstothe
cochlea,aspiral-shapedstructure.Thecochleaconsistsof
threefluid-filledspaces:thevestibularduct,thecochlearduct,
andthetympanicduct.Haircellsresponsible
fortransduction—changingmechanicalchangesinto
electricalstimuliarepresentintheorganofCortiinthe
cochlea.

13. Blood supply
The blood supply of the ear differs according to each part of the ear.
Theposterior auricular artery
Theanterior auricular arteries
thesuperficial temporal artery.
Theoccipital artery
themaxillary artery
themiddle meningeal artery,
ascending pharyngeal artery,
internal carotid artery, and
the artery of thepterygoid canal.
thelabyrinthine artery,
theanterior inferior cerebellar arteryor thebasilar artery.

14. Venous Drainage :
pterygoid plexus,
external jugularand
maxillary veins.

15. Innervation
temporal branch of thefacial nerve
theposterior auricular branch of the facial nerve
thegreat auricular nerve
auriculotemporal nerve
auriculotemporal branch of the mandibular nerve
theauricular branch of the vagus nerve
theauricular branch of the vagus nerve

16. Clinical significance :
•Hearing loss
•Congenital abnormalities
Vertigo
•Tinnitus