structure of ear,function,hearing disorders

3. SOUND
SOUND WAVES

5. S – shaped Curve or Sine Wave
Frequency
- number of waves that
pass a given point in a
given time (cycles/sec)
Amplitude
- height of the wave

6.  transmission of sound depends on elastic
medium
 travels more slowly than light
 light --- 300,000 km/s (186,000 miles/s)
 sound --- 0.331 – 0.344 km/s (0.2 miles/s) -- 20o
C
at sea level (↑ with temperature and altitude)
 speed of sound
 solid > liquid > air

8. LOUDNESS
- correlated with amplitude
- measured in decibels (dB)
- 1 dB = 0.01 bel
intensity of sound
log -------------------------- 0 dB (1000 Hz)
standard sound
- 120–160 dB (painful), 90–110
extremely high , 60- 80 very loud
40-50 moderate and 30 faint
PITCH
- correlated with frequency
- frequency range audible to
human ear is 20 – 20,000
cycles/sec (Hertz)
- greatest sensitivity ranges
from 1,000 – 4,000 cycles/sec
- best pitch discrimination is
1,000 – 3,000 cycles/sec

18. EXTERNAL AUDITORY CANAL
- transmits sound pressure waves
to the tympanic membrane
- contains glands that secrete
cerumen
EXTERNAL EAR
PINNA
- funnels sound wave to the
external auditory meatus
- plays a role in sound
localization

19.  The Ear has 3 parts: External, Middle and the
Internal ear.
 The External Ear
 (1) Pinna: Helps to collect sound waves and to
localize the source of sound. In lower animals
Pinna can be moved by muscular actions in
the direction of sound source to collect sound
in humans these muscles have little action.

20.  (2) External Auditory canal- 2.5 cm long
(i)helps in transporting the sound waves to the
middle ear (ii) secrete wax and oil trap the
foreign bodies.

23.  The Middle Ear
 An air filled cavity within the temporal bone
that consist of
 (i)Tympanic Membrane.(ear drum)
Functions–
 Pressure Receiver i.e extremely sensitive to
pressure changes
 Resonator i.e. it starts vibrating freely when
the sound waves strike
 Critically dampens the sound waves i.e.as
soon the sound will stop T.M. vibrations are
stopped immediately

24.  (ii) Ear Ossicles
 Malleus-resembles a hammer.The handle of malleus is connected to the inner
surface of T.M.
 Incus-It articulate with head of malleus
 Stapes- looks like stirrup. The head of stapes articulates with incus & the oval
foot plate contact the oval window of the coclea
 function= to magnify the intensity of sound by 1.2 to 1.3 times by lever action.

26.  Middle ear mucles(a) Tensor tympani=
attached to the neck of malleus .its
contraction tenson of tympanic
membrane (b) Stapedius: attached to the
neck of stapes and on contraction it pulls
the foot plate of stapes out from the oval
window
 Function= both the muscles can be reflexley
activated by loud sounds amplitude of
sound vibration of the tympanic membrane
protection of the internal ear from loud
sounds(Tympanic Reflex. reaction time40-
160sec)

27. Middle ear mucles(a)
Tensor tympani= attached
to the neck of malleus .its
contraction tenson of
tympanic membrane (b)
Stapedius: attached to the
neck of stapes and on
contraction it pulls the
foot plate of stapes out
from the oval window

28. MIDDLE EAR
OSSICLES
- malleus, incus and stapes
- transmit vibratory motion
of the tympanic membrane
to the oval window
TENSOR TYMPANI MUSCLE
- contraction pulls manubrium
of the malleus
- decreases the vibration of
tympanic membrane
STAPEDIUS
- contraction pulls the
footplate of the stapes out of
the oval window

29.  function of the muscles and ossicles
 Functions
 protect the cochlea from damaging vibrations
caused by excessively loud sounds
 mask low frequency sounds in loud
environments
 decrease persons sensitivity to his or her own
speech (muscles)

30.  latency ---- 40 to 80 milliseconds
 contraction of tensor tympani and
stapedius dampens the movement and
ossicles and decreases the sensitivity of
acoustic apparatus.
 reduce intensity of sound transmission by
30 – 40 dB (↓ 1000 cycles/second)

31. Pharyngotym-
panic tube
Tensor
tympani
muscle
Tympanic
membrane
(medial view)
Stapes
Malleus
Superior
Anterior
Incus Epitympanic recess
Stapedius
muscle

32.  Role of Middle Ear
 The ear ossicles result in magnification of
sound intensity by 1.2-1.3 times
 The effective surface area of T.M.=55sq.mm
and that of oval window is 3sq.mm,thus
reduction of the area is by @17times(55/3)
 Total magnification=22times(17Х1.3)

35.  Effective transfer of sound energy from air to
fluid medium is difficult because most of the
sound is reflected as a result of the different
mechanical properties of the two media. The
middle ear thus act as an impedance
matching device by amplifying the sound
pressure
 Amplification of sound intensity is greatest
between 1000-3000 Hz .sounds below 16Hz
or above 20000Hz are not amplified at all.

36. Fluids in cochlear canals
Upper and middle
Internal earExternal ear
Pinna
External
acoustic
meatus
Air
Tympanic
membrane
Malleus, incus,
stapes
(ossicles)
Oval
window Lower
Middle ear
One
vibration
Time
Spiral organ
(of Corti)
stimulated
Amplification
in middle ear
Amplitude
Pressure

37. SOUND TRANSMISSION

38.  inflammation of the middle ear
 commonly due to infection and common
result of a sore throat especially in
children
 eardrum bulges and becomes inflammed
and red ------- pain and rupture

39. MIDDLE EAR
AUDITORY TUBE
- formerly called eustachian tube
- link the middle ear with the
pharynx
- opening equalizes pressure in
the middle ear cavity with
external air pressure

42. BONY LABYRINTH
MEMBRANOUS LABYRINTH

43.  Boney labyrinth and membranous labyrith
 Membranous labyrinth comprises one
vestibule(utricle and saccule) and three
semicircular canals.-concerned with
equilibrium. One Coclea concerned with
hearing

45. INNER EAR (Labyrinth)
COCHLEA
- involved in hearing
SEMICIRCULAR CANAL
- involved in equilibrium
- receptors detect rotational
acceleration
UTRICLE
- involved in equilibrium
- receptors detect linear
acceleration (horizontal
direction)
SACCULE
- involved in equilibrium
- receptors detect linear
acceleration (vertical
direction)

47. 47
• Stapes pushes on fluid of vestibular duct at oval window
• At helicotrema, vibration moves into tympanic duct
• Fluid vibration dissipated at round window which bulges
• The central structure is vibrated (cochlear duct)
helicotrema
vestibular duct
tympanic duct
round
window
Cochlear duct
containing the Organ
of Corti
Cochlea Uncoiled
oval
window

54. COCHLEA

55. ORGAN OF CORTI

60. 60
helicotrema
vestibular duct
tympanic duct
round
window
Cochlear duct
containing the Organ
of Corti
Cochlea Uncoiled
oval
window

69. BASILAR MEMBRANE…..VIBRATES
TECTORIAL MEMBRANE STATIONARY
STEROCILIA
AUDITORY
NERVE
HAIR
CELLS

70. TECTORIAL MEMBRANE STATIONARY
BASILAR MEMBRANE…..VIBRATES
STEROCILIA
BEND
AUDITORY
NERVE HAIR
CELLS

71. ELECTRICAL RESPONSES OF HAIR CELLS
GENESIS OF ACTION POTENTIALS IN AFFERENT NERVES

72. Sound waves
Tympanic membrane vibrations
Ossicles transmit & amplify vibration
Via oval window to perilymph then endolymph

73. Vibrations in perilymph are
transferred across the basilar
membrane to the cochlear duct
Vibrations in endolymph stimulate
sets of receptor cells
Receptor (hair) cells release NT
which stimulates nearby sensory
neuron
Impulse to auditory cortex of
temporal lobe via Cochlear nerve
to Vestibulocochlear N. (VIII)

76.  apex is wider than
the base
 tension is higher at
the base than at the
apex
 base vibrate at
higher frequency
than the apex
(frequency analyzer)

77.  length of the fibers is
greater at the apex than at
the base
 fiber diameter is greater at
the base than at the apex
 base -- shorter and wider
 apex – taller and slender
 high –frequency resonance
(base), low frequency
resonance (apex)

78. (a)
(b) (c)
Stapes
Oval
window
Scala
vestibuli
Cochlear
duct
Scala
tympani
Basilar
membrane
Round
window
Base
Hz
20,000
(High notes)
Hz
1500
Hz
500
500 Hz
4000 Hz
24,000 HzHz
20
(Low notes)
Apex
Perilymph
Cochlear
nerve
Relative
lengths
of basilar
fibers
within
different
regions
of basilar
membrane
Basilar
membrane

80. PLACE THEORY OF HEARING

86.  the frequency of
action potential in
single auditory nerve
is proportional to the
loudness of the sound
stimuli.

92. 10-60

94.  time lag between the entry of sound into one ear
and its entry into the opposite ear.
 functions best at frequencies below 3,000 cycles/sec.
 neural analysis ---- medial superior olivary nucleus
 difference between the intensities of the sounds
in the two ears.
 functions best at frequencies above 3,000 cycles per
second
 neural analysis ---- lateral suprior olivary nucleus

96. CONDUCTIVE DEAFNESS SENSORINEURAL DEAFNESS
 due to impaired sound
transmission in external and
middle ear
 impacts all sound frequencies
 Causes
 plugging of the EAC with
cerumen(wax) / foreign bodies
 otitis externa and otitis media
 perforation of eardrum
 Otosclerosis(immobility of
ossicles)
 Rupture of Auditory ossicles
 due to loss of cochlear hair cells
(common), problems with the eight
cranial nerves or within central
auditory pathways (nerve deafness)
 impairs the ability to hear certain
pitches (permanent)
 Causes
 Exposure to sudden large intensity noise
 Aoto-toxic drugs
 aminoglycoside antibiotics
(streptomycin,Quinine,Frusemide,Tobr
amycin,Kenamycine gentamycin)
 prolonged exposure to noise
 tumors and vascular damage

99.  Conduction deafness:
 Transmission of sound waves through middle
ear to oval window impaired.
 Impairs all sound frequencies.
 Hearing aids.
 Sensorineural (perception) deafness:
 Transmission of nerve impulses is impaired.
 Impairs ability to hear some pitches more than
others.
 Cochlear implants.

103. (b)
Pharyngotympanic
(auditory) tube
Auditory
ossicles
Entrance to mastoid antrum
in the epitympanic recess
Tympanic
membrane
Semicircular
canals
Cochlea
Cochlear
nerve
Vestibular
nerve
Oval window
(deep to stapes)
Round window
Incus
(anvil)
Malleus
(hammer)
Stapes
(stirrup)
Internal
jugular vein
Vestibule
External
acoustic
meatus

105.  Ossicular Conduction
 main pathway for normal hearing
 Air Conduction
 unimportant for normal hearing
 initiated by vibration of round window
 Bone Conduction
 involves skull bones
 plays a role in transmission of extremely loud
sounds

106. Table 9–1. Common Tests with a Tuning Fork to Distinguish between Nerve
and Conduction Deafness.
Weber Rinne Schwabach
Method Base of vibrating tuning
fork placed on vertex of
skull.
Base of vibrating tuning
fork placed on mastoid
process until subject no
longer hears it, then held
in air next to ear.
Bone conduction of
patient compared with that
of normal subject.
Normal Hears equally on both
sides.
Hears vibration in air after
bone conduction is over.
Conduction deafness (one
ear)
Sound louder in diseased
ear because masking
effect of environmental
noise is absent on
diseased side.
Vibrations in air not heard
after bone conduction is
over.
Bone conduction better
than normal (conduction
defect excludes masking
noise).
Nerve deafness (one ear) Sound louder in normal
ear.
Vibration heard in air after
bone conduction is over,
as long as nerve deafness
is partial.
Bone conduction worse
than normal.

111. The Weber and Rinne tuning fork tests are used to differentiate
conductive hearing loss from sensorineural hearing loss.

113.  presence of one sound decreases an
individual’s ability to hear other sounds
 due to the relative and absolute
refractoriness of previously stimulated
auditory receptors and nerve fibers to
other stimuli.

117. Audiometry
Auditory acuity is commonly
measured with an audiometer.
This device presents the subject
with pure tones of various
frequencies through earphones. At
each frequency, the threshold
intensity is determined and
plotted on a graph as a
percentage of normal hearing.
This provides an objective
measurement of the degree of
deafness and a picture of the
tonal range most affected.