Ear, its functions and problems causing Deafness.pptx

cerumen impaction (impacted ear wax)
trauma to the ear or head.
loud noise/loud sounds.
ototoxic medicines.
work related ototoxic chemicals.
nutritional deficiencies.
viral infections and other ear conditions.
delayed onset or progressive genetic hearing loss.

1. EAR AND IT’S PROBLEMS CAUSING DEAFNESS DR MUNIR AHMED AUDIOLOGIST AND AUDITORY REHAB SPECIALIST Mob: [phone] E.mail : [email protected]

2. THE AURICLE Auricle gives beauty and funnel sound into External Auditory canal (EAC) It helps to localize sound and amplify high frequencies slightly (5000 Hz) It’s tragus is an efficient mean to block sound It holds full concha ear molds of hearing aids

3. EXTERNAL AUDITORY CANAL (EAC) EAC (being curve) protects ear from foreign bodies and trauma It serves as filter and resonator It reduces low frequencies and enhance high frequencies (between 2 to 7KHz) Sound around these frequencies is amplified about 10 to 15 dB

4. TYMPANIC MEMBRANE M embrane is about 63.3 square mm (55 square mm is pars tensa and remaining is pars flacidda ) Outer layer is made of skin, an incomplete middle layer is made of fibrous connective tissue and inner is mucous Movement of one billionth of centimeter is sufficient to produce threshold in normal hearing individuals between 800 to 6000 Hz It appears red when infected

5. DISORDERS OF OUTER EAR D isorders may be due to congenital or acquired conditions Congenital Conditions Anotia (No pinna)

6. Contd -- Microtia : Poorly developed pinna; May be small deformed shaped pinna, extra pinna or a tag of soft tissue

7. Contd -- Atresia: Complete closure or absent of external auditory meatus Stenosis of EAC: Narrowing may be due to overgrowth of bone Aural Fistula : Sinus may lead from the skin

8. Contd-- Middle ear communicates with nasopharynx via eustachian tubes In young children, eustachian tubes are shorter, wider and more horizontal, so babies are much more prone to middle ear disease Three ossicles Malleus (Hammer), incus (anvil) and stapes (stirrup)} and their muscular attachments: tenser tympani and stapedius

9. Contd -- It’s central bulge; promontory , forms first turn of cochlea Stimulus more than 80 dB from threshold contracts ear muscle (tenser tympani and stapedial) to save from damage, these a coustic reflexes can be measured while analyzing middle ear status Ossicles of middle ear serve to transmit sound energy from tympanic membrane to cochlea Footplate of stapes closes oval window, which communicates with perilymph of cochlea. Oval window separate middle ear from Scala vestibule

10. Contd -- Below and behind the promontory is round window that separate middle ear from Scala tympani Middle ear conducts sound to cochlea and ossicles assure appropriate stimulation of inner ear Pressure at oval window is 17times greater than tympanic membrane (55/3.2 mm). It amplify about 25 dB and lever action 2 dB

11. PATHOLOGY OF MIDDLE EAR Some Congenital Conditions of Middle Ear includes : Treacher Collin’s Syndrome, it’s characteristics includes Poorly formed cheek bones Fish like mouth Slopping eyes Nicks in the eyelids Poorly developed outer and middle ear, often with atresia. Hearing loss is mainly conductive

12. Contd --- Crouzon’s syndrome , its characteristics includes Mid face abnormally shaped Head with central prominence in frontal region Hearing loss is mainly conductive Paget’s diseases , it’s Characteristics includes Progressive deformities become apparent around 2nd year of life Mixed progressive hearing loss due to bone formation at base of skull

13. Contd --- Down’s syndrome: it’s Characteristics includes Learning difficulties with classical features with small pinna and narrow ear canal Type of Hearing loss may be; conductive, sensorineural or mixed

14. Contd---

15. Contd--- ACQUIRED CONDITIONS OF MIDDLE EAR Direct trauma ; by poking object into middle ear Indirect trauma A blow at side of head may damage temporal bone usually symptoms are; bleeding, bruising and deafness CT Scan may show fracture in temporal area

16. Contd--- Barotraumas Rapid alteration in air pressure causes barotraumas, that may be due to sudden decent of aircraft or rapid decent in deep sea Otosclorosis In otosclerosis, foot plate of stapes became immoveable due to growth of spongy type bone especially around the oval window causes: Conductive hearing loss especially on low frequencies A dip on BC threshold at 2 kHz ( carhart’s notch)

17. Contd--- Cholesteatoma A pouch (filled with Skin, dust, wax etc) may be formed due to raised pressure in EAC by pushing the flaccid part of the ear drum when eustachian tube remain un-patent Later on Cholesteatoma may develop owing to constant lower pressure in middle ear. if not treated, it may destroy ossicular chain and erode the roof of the middle ear

18. Contd --- Otitis Media with Effusion (glue ear) : Due to un patent eustachian tubes negative pressure may develop in middle ear cavity. Initially ear drum is retracted if not managed, then bulged outwards due to effusions. Usually it resolves spontaneously, if not then treated with medical or surgical intervention

19. Contd - -- Children are prone to glue ear as their eustachian tube is short , narrow and more horizontal than adults some times drum bursts and fluid is released from glue ear Malformation, damage or disease in any part of the middle ear causes conductive hearing loss

20. THE INNER EAR It is so small that can be compared with small pea Footplate of stapes fits on oval window Cochlea is a coiled and snail shaped organ, has approximately 2 ¾ turns Beyond oval window is scala vestibule cochlea’s upper chamber

21. Contd-- Beyond round window: at the bottom of cochlea is scala tympani Cochlea’s lower chamber Middle chamber between these two chambers is Scala media or cochlear duct, filled with endolymph Scala media separated from scala vestibule by Reissners’s membrane and scala tympani by basilar membrane

22. Contd-- The scala vestibuli and scala tympani are filled with perilymph; high in it’s concentration of sodium and low in potassium Scala media is filled with endolymph; high in it’s concentration of potassium and low in sodium The basilar membrane forms scala media floor

23. Contd-- The scala vestibuli and scala tympani are filled with perilymph; high in it’s concentration of sodium and low in potassium Scala media is filled with endolymph; high in it’s concentration of potassium and low in sodium Basilar membrane is about 35mm long and varies in width; Base 0.1 mm, narrow and stiff; Apex 0.5 mm broad. Reverse of cochlear duct. Hair cells lies on basilar membrane 3 to 5 parallel rows of 12,000 to 15,000 outer hair cells ( OHCs) and one row of 3,000 inner hair cells (IHCs)

24. Contd-- A uditory nerve endings are located on basilar membrane S ome of nerve fibers connects to hair cells in one to one relationship, while others make contacts with many hair cells H air cells are about 0.01mm long and 0.001 mm in diameter The outer and inner hair cells are separated by Corti arch Direction in which HCs bent during stimulation is of great importance; if cilia bent in one direction nerve cells are stimulated ,

25. Contd--- If they bend other way nerve impulses are inhibited if they bend to side there is no stimulation at all Tuning of basilar membrane is very important

26. Contd-- S hape of organ of corti and basilar membrane changes along length of Cochlea ; widest at apex narrow at base Auditory Nerve fibers are sharply tuned to specific frequencies; l owest frequencies around 20 Hz at apical end of cochlea. 2000 to 20,000 Hz from midpoint of BM to the basal end of cochlea Below 2000 Hz on the other half of BM

27. Contd-- Nerve fibers exit cochlea and extend centrally to ward the modiolus Cell bodies of nerve fibers group together to form Spiral Ganglion. Nerve fibers pass modiolus to form cochlear branch of auditory nerve (VIII Cranial nerve )

28. Contd--

29. FUNCTIONS OF COCHLEA Cochlea analyses sound into component frequencies before relaying to auditory areas of brain; higher frequencies at base, m id frequencies at mid and lower frequencies at apex Two processes are carried out in cochlea; Transmission process and Transduction process By Transmission process ; Acoustic energy is transferred from oval window to organ of corti By Transduction process; sound energy is converted into electrical impulses in auditory nerve fibers

30. Contd-- In transmission process rocking of stapes pressed oval window that create pressure in perilymph Pressure bulges out round window and wave is set up in endolymph within membranous sac This wave travel along basilar membrane; beginning from base towards the apex of the cochlea At point where maximum displacement is attained is a peak of wave depends upon the frequency Lower frequencies passes further along the membrane and its peak is near apex

31. Contd-- It is assumed that transduction of hair cells may be mechanical or electrical or chemical Mechanical hypothesis assumes that pressure which moves hair cells; stimulates nerve endings directly Electrical hypothesis assumes that cochlear potential stimulates nerve ending. Chemical hypothesis assumes that when hair cells deformed, a neurotransmitter substances released that stimulates nerve endings

32. Contd--- In resting position Endolymph outside the hair cells has positive charge 80 microvolt approx Inside the hair cell negative charge –60 microvolt approx When transduction link tightened, trap door opens at top of the cilia, in results hair cells become more positively charged Higher intensity sound produces more firing but not larger potentials

33. Contd-- When wave travels; it first moves forward and upward, then backward and downward Stereocilia of hair cells is embedded in tectorial membrane This shearing motion bends stereocilia first towards the tallest stereocilia and then other way. Joining their tips are “transduction links” The tension is alternately tightened and released The tuning of basilar membrane is important for frequency discrimination

34. Contd-- The neurotransmitters are stimulated at the base of cell, which fire the nerve impulses These nerve impulses are known as action potential, that can be recorded by placing electrodes in near field or sometimes far field areas

35. Contd--- One axon terminates at the base of nerve cell and other in the cochlear nucleus of brainstem The cell bodies are grouped in osseous spiral lamina and thus called spiral ganglion From spiral ganglion, nerve fiber joins together to form cochlear nerve and pass through internal auditory canal Malformation, damage or disease occurring in any part of perceptive apparatus may cause sensorineural hearing loss Nerve cells are bi-polar. Each has a body and two axons

36. Contd--- From here nerve divides into two and terminates into ventral and dorsal cochlear nuclei This pathway continue via Lateral Lemniscus, the Inferior Colliculus, the Medial Geniculate body and then auditory cortex Most fibers from these nuclei crosses over to superior olivary nucleus of opposite hemisphere However some follows pathway on same side Thus cortex of each hemisphere receives information from both ears

37. Contd--- But majority of information received in left auditory cortex will have originated in right ear

38. LABYRINTH - HEARING LOSS Largely, problem in labyrinth causes sensorineural hearing loss ( HL) Cochlear HL originates with pathology at the level of hair cells Alteration in structure and function of cochlea produce more hearing loss than do abnormalities in other areas of sensorineural system Diseases or abnormalities may be prenatally, perinatally and postnatally

39. Contd-- Owing to genetic abnormalities inner ear may be poorly developed Many congenital hearing losses of unknown reasons are also developed : few of them are Usher’s syndrome Moderate to severe bilateral hearing loss present at birth Progressive blindness specially starts at teens Waardenburg’s Syndrome Mild to profound (sometimes progressive ) hearing loss may be unilateral or bilateral

40. Contd-- White forelock and different colored segments in eyes Turner’s Syndrome Mild Sensorineural and conductive hearing loss in females Low hear line, Webbed neck, Short stature, Kidney’s defect etc Rubella (German Measles) Viral infection contracted from mother during pregnancy causes hearing loss

41. Contd-- The child may have Heart diseases, Eye disorder, Psycho motor problems and Behavior problem Cytomeglovirus Diseases (CMV) Viral infection contracted from mother during pregnancy or during birth Child may have hearing loss, learning difficulties, spasticity, convulsions and hyperactivity Syphilis Bacterial infection contracted from mother during pregnancy may cause slow progressive deafness

42. Contd-- Mumps Measles, Shingles, Diphtheria, Meningitis Mumps usually causes unilateral hearing loss Measles may complicated by otitis media Shingles (Herpes Zoster ) causes inflammation of nerves, when auditory nerve involves cause sensorineural hearing loss with pain Diphtheria may cause sensorineural hearing loss with secondary otitis media Meningitis may cause profound bilateral Sensorineural hearing loss

43. Contd --- Mènière disease Usually occurred in middle age with unknown causes, it is known to be associated with raised pressure and distension of membranous labyrinth ( hydrop ) Disorder is characterized by sudden attack of vertigo, tinnitus, vomiting, unilateral deafness and sensation of fullness in one ear followed by low-frequency roaring tinnitus Hearing loss with great difficulty in speech recognition

44. Contd--- Presbyacusis In old age, degenerated changes in auditory system causes hearing loss It may occur due to Impaired blood supply, poor diet, medication, lack of exercise, stress etc Acoustic Neuroma It is a benign, local and slow growing tumors of the VIII cranial nerve The condition is relatively rare having an incident of 1 in 100,000

45. Contd - -- Intense short duration sound such as gunfire may cause sudden high frequency hearing loss Children develop hearing loss due to exposure to high intensity noises produced by toy phones , guns , musical instrument, fire crackers etc

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