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AUDITORY ORGAN
Mukhamedzhano A.Kh.
Candida e o Medical Sciences
Rezyapo a D.R.
Uma o a X.M.
Al aganus Uni e si y non-go e nmen al o ganiza ion highe educa ion,
Tashken , Uzbekis an.
h ps://doi.o g/10.5281/zenodo.17332247
Anno a ion. This e iew summa izes he ana omy, cellula physiology, neu al pa hways
and cen al p ocessing o he audi o y sys em. Pe iphe al s uc u es (ou e , middle and inne
ea ), mechanoelec ical ansduc ion by hai cells, cochlea mechanics and equency mapping
a e desc ibed. Ascending audi o y pa hways om he cochlea ne e h ough b ains em nuclei o
he audi o y co ex a e ou lined, including pa allel p ocessing o iming and in ensi y cues.
Clinical aspec s such as hea ing loss ypes, diagnos ic me hods (audiome y, o oacous ic
emissions, audi o y b ains em esponses), and cu en he apeu ic and ehabili a i e app oaches
(hea ing aids, cochlea implan s, pha macological and gene he apies) a e discussed. Eme ging
di ec ions in audi o y neu oscience, including hai cell egene a ion, op ogene ic s imula ion
and b ain–compu e audi o y in e aces, a e highligh ed.
Keywo ds: hea ing, audi o y o gan, cochlea, hai cells, cochlea ne e, audi o y co ex,
o oacous ic emissions, cochlea implan , audi o y b ains em esponse.
In oduc ion:
Hea ing is a undamen al senso y modali y o communica ion, spa ial o ien a ion and
en i onmen al awa eness. The audi o y o gan ans o ms ai bo ne sound p essu e wa es in o
neu al signals ia inely uned mechanical and cellula mechanisms. The sys em suppo s
exquisi e equency disc imina ion, empo al esolu ion and sound sou ce localiza ion.
Unde s anding i s s uc u e and unc ion is essen ial o diagnosing and ea ing hea ing
diso de s, which a ec hund eds o millions wo ldwide.
Pe iphe al ana omy and mechanics
1.Ou e ea
- Pinna and ex e nal audi o y canal collec and unnel sound o he ympanic memb ane,
p o iding di ec ional cues and equency-dependen ampli ica ion, pa icula ly o high
equencies.
2.Middle ea
- Tympanic memb ane ansmi s ib a ions ia he ossicula chain (malleus, incus, s apes)
o he o al window. The ossicles p o ide impedance ma ching be ween ai and cochlea luids
h ough le e ac ion and a ea a io, inc easing ene gy ans e .
- Middle ea muscles ( enso ympani, s apedius) modula e ansmission, p o ec ing he
cochlea om in ense sounds and in luencing acous ic e lexes.
3.Inne ea
- The cochlea is a coiled, luid‑ illed o gan pa i ioned by he basila memb ane in o scala
es ibuli and scala ympani wi h scala media (endolymph) be ween.
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The basila memb ane exhibi s ono opic mechanical p ope ies: base is na ow and s i
o high equencies; apex is wide and complian o low equencies.
- Mechanical a eling wa e gene a ed by s apes mo emen peaks a a loca ion
de e mined by s imulus equency, p o iding place coding o pi ch.
Cellula ansduc ion and cochlea ampli ica ion
- O gan o Co i con ains inne hai cells (IHCs) and ou e hai cells (OHCs). IHCs a e
p ima y senso y ecep o s ha elease neu o ansmi e on o ype I a e en ibe s o he cochlea
(VIII) ne e. OHCs p o ide ac i e elec omechanical ampli ica ion ia soma ic mo ili y d i en
by p es in, enhancing sensi i i y and equency selec i i y.
- Hai bundle de lec ion opens mechanoelec ical ansduc ion (MET) channels, allowing
K+ and Ca2+ in lux om endolymph and causing ecep o po en ials. Fas synap ic ansmission
a IHC ibbon synapses suppo s high empo al ideli y.
- Endocochlea po en ial (≈+80 o +100 mV) main ained by s ia ascula is d i es ionic
cu en s and is essen ial o ansduc ion.
Audi o y ne e and b ains em p ocessing
- Spi al ganglion neu ons ( ype I myelina ed neu ons) inne a e IHCs wi h a 1:1–2:1 a io
in many mammals; ype II neu ons inne a e OHCs spa sely.
- Cochlea ne e ibe s p ese e ono opy and phase-locking o s imulus wa e o m a low
o mid equencies; ibe spon aneous a es and h esholds a y, con ibu ing o dynamic ange
encoding.
- B ains em nuclei p ocess sound ea u es in pa allel
- Cochlea nucleus subdi ides in o do sal and en al sec o s ex ac ing spec al cues and
empo al ine s uc u e.
- Supe io oli a y complex pe o ms binau al p ocessing: medial supe io oli e (MSO)
compu es in e au al ime di e ences (ITD) o low equencies; la e al supe io oli e (LSO)
p ocesses in e au al le el di e ences (ILD) o high equencies.
- Nuclei o he la e al lemniscus and in e io colliculus in eg a e empo al and spec al
in o ma ion and con ibu e o audi o y e lexes and a en ion.
Thalamoco ical and co ical pa hways
- In e io colliculus p ojec s o he medial genicula e body (MGB) o he halamus, which
elays o p ima y audi o y co ex (A1) loca ed on Heschl’s gy us in humans. Tono opic
o ganiza ion pe sis s h oughou hese s a ions.
- Audi o y co ex p ocesses complex ea u es (ha monics, empo al pa e ns), suppo s
sound objec ecogni ion, language p ocessing and audi o y scene analysis. Ex ensi e
co ico ugal p ojec ions modula e b ains em and cochlea unc ion, media ing a en ion and
plas ici y.
Physiology o sound pe cep ion
- F equency coding combines place and empo al mechanisms; in ensi y coded by i ing
a e, ec ui men o ibe s and sp ead o exci a ion.
- Tempo al esolu ion unde pins speech pe cep ion and localiza ion; comodula ion
masking elease and binau al unmasking imp o e signal de ec ion in noise.
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- Plas ici y allows aining-induced imp o emen s and compensa o y changes ollowing
pe iphe al damage.
Clinical aspec s
Types and causes o hea ing loss
- Conduc i e hea ing loss a ises om ou e /middle ea dys unc ion (ce umen, o i is
media, o oscle osis).
- Senso ineu al hea ing loss (SNHL) esul s om hai cell loss, synap opa hy, spi al
ganglion degene a ion o s ial dys unc ion; causes include noise exposu e, aging (p esbycusis),
o o oxic d ugs, gene ic de ec s and in ec ions.
- Hidden hea ing loss e e s o synap opa hy educing sup a h eshold coding while
audiome ic h esholds emain no mal.
- Cen al audi o y p ocessing diso de s in ol e de ici s in co ical o b ains em
p ocessing.
Diagnos ic me hods
- Pu e- one audiome y assesses h esholds and ai -bone gaps.
- Speech audiome y e alua es unc ional hea ing o communica ion.
- O oacous ic emissions (OAEs) p obe OHC unc ion; absence o OAEs sugges s
cochlea ampli ie impai men .
- Audi o y b ains em esponses (ABR) p o ide objec i e assessmen o neu al iming and
in eg i y up o b ains em, use ul in newbo n sc eening and e ocochlea pa hology de ec ion.
- Elec ocochleog aphy measu es cochlea po en ials; high- esolu ion imaging (CT/MRI)
de ec s s uc u al causes.
T ea men and ehabili a ion
- Medical and su gical managemen o conduc i e causes ( ympanoplas y, ossiculoplas y,
s apedec omy).
- Hea ing aids ampli y sound and use signal p ocessing o imp o e speech audibili y;
bene i s depend on esidual cochlea unc ion.
- Cochlea implan s bypass hai cell ansduc ion by elec ically s imula ing spi al
ganglion neu ons; sui able o se e e- o-p o ound SNHL. Ad ances include elec ode design,
coding s a egies and bila e al implan a ion.
- Eme ging biological he apies aim o egene a e hai cells using gene he apy (A oh1),
i al ec o s, small molecules and s em-cell app oaches. Clinical ansla ion aces challenges in
a ge ed deli e y and unc ional in eg a ion.
- O o oxici y p e en ion, noise con ol, inni us managemen and audi o y ehabili a ion
p og ams complemen de ice-based ea men s.
Technological and esea ch on ie s
- Op ogene ic cochlea s imula ion p omises imp o ed spa ial selec i i y compa ed wi h
elec ical s imula ion.
- Neu al p os heses in eg a ing co ical in e aces and audi o y b ains em implan s a e
unde de elopmen o cases wi h absen audi o y ne e.
- Single-cell ansc ip omics e ines cellula axonomy o cochlea and audi o y b ain
s uc u es, guiding a ge ed he apies.
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- Bioma ke s o synap opa hy and ea ly degene a ion a e sough o enable imely
in e en ions.
Conclusion:
The audi o y o gan is a highly specialized sys em combining mechanical, cellula and
neu al mechanisms o ansduce and p ocess sound wi h ema kable ideli y. Clinical
managemen o hea ing diso de s has ad anced om p os he ic ampli ica ion o neu al implan s
and expe imen al egene a i e s a egies. Con inued in e disciplina y esea ch in molecula
biology, enginee ing and sys ems neu oscience is essen ial o es o e and enhance hea ing ac oss
he li espan.
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