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Hearing
Introduction
• Hearing is the ability to perceive sound by
detecting vibrations through an ear. It is also
called Audition
• It is a type of Mechanoreceptor sense
Anatomy of EAR
The ear is formed of three
anatomical and functional
parts:
 Outer ear – functions in
hearing
 Middle ear – functions in
hearing
 Inner ear – functions in
both hearing and
equilibrium
Outer (external) Ear
Involved in hearing only
Structures of the external
ear
 Pinna (auricle)
 External auditory
canal
 Tympanic
membrane
The Middle Ear or Tympanic
Cavity
Air-filled cavity within
the temporal bone
Only involved in the
sense of hearing
3 bones (ossicles) :
Malleus , Incus & Stapes
2 muscles
Tensor tympani &
Stapedius
The Eustachian tube
Inner Ear or Bony Labyrinth
Includes sense organs
for hearing & balance
Filled with perilymph
Bony labyrinth
cochlea
vestibule
3 semicircular canals
Membranous labyrinth
Organ of hearing
Organ of Corti
 The receptor epithelium for hearing
 Located within the cochlea
 Hearing receptors  hair cells on the basilar
membrane
 Gel-like tectorial membrane is capable of
bending hair cells
 Cochlear nerve attached to hair cells transmits
nerve impulses to auditory cortex on temporal
lobe
Physiology of Hearing
1. The auricle directs sound waves into the external
auditory canal.
2. Sound waves strike the tympanic membrane
causes it to vibrate back and forth. The distance it
moves depends upon the intensity and frequency
of the waves.
3. The central eardrum connects to the Malleus,
which also starts to vibrate. This vibration is then
transmitted to the Incus and Stapes.
4. As the stapes moves back and forth, it pushes the
membrane of the oval window in and out.
Cont…
5. The movement of the oval window sets up fluid
pressure waves in the perilymph of the cochlea.
6. Pressure waves are transmitted to the round
window, causing it to bulge outward.
7. These waves in turn create pressure waves in
the endolymph of the cochlear duct.
8. This causes the basilar membrane to vibrate,
which moves the hair cells leading to receptor
potentials and ultimately nerve impulses.
Video …
Auditory Pathway
• Sound waves are transmitted as electrical waves
through the 8th nerve to the cochlear nuclei on
each side of medulla (which has two nuclei
dorsal and ventral cochlear nucleus)
• Fibers from ventral nucleus (which is concerned
in time difference) will relay into the superior
olivary complex in the pons , and some little
fibers from dorsal cochlear nucleus will relay
there too.
Auditory Pathway
• Most fibers from the dorsal cochlear nucleus
(concerned in quality of sound) go directly to the
inferior colliculus of midbrain.
• The inferior colliculus also receives fibers from
superior olivary nucleus.
• The lateral lemniscus is a tract of axons in the
brainstem that connects the previous nuclei
together and carrying auditory signal inbetween.
Auditory Pathway
• From the inferior colliculus Then fibers go to the
medial geniculate body in the thalamus, then to
the primary auditory cortex in the temporal lobe.
• The area in cortex concerned with hearing
situated in the superior temporal gyrus
(Brodmann’s area 41,42).
When hearing tests are required?
Hearing tests are performed in the conditions
mentioned below.
• Hearing impairment
• As a part of routine assessment of child
development
• Maybe a part of general medical examination
• Maybe used to know the cause of Tinnitus
When to suspect hearing
problems?
When to suspect hearing
problems?
 Do you have a problem hearing over the telephone?
 Do you hear better through one ear than the other?
 Do you have trouble following the conversation with
two or more people talking at the same time?
 Do people complain that you turn the TV volume up
too high?
 Do you have dizziness, pain, or ringing in your ears?
 Do you have trouble understanding the speech of
women and children?
Hearing impairment
Hearing impairment :
Diminution in the acuity of hearing
Types of hearing loss:
Conductive hearing loss.
Perceptive or sensorineural hearing loss.
Mixed type.
How hearing tests are done?
Hearing of a person can be tested by two methods:
Clinical tests
Audiometric tests
A . Clinical Tests
 Finger Friction Test
 Watch Test
 Speech Test
 Tuning Fork Tests
Finger Friction Test
• Is a quick and rough
method of testing
hearing by rubbing
the thumb and the
finger close to the
patients ear and ask
if the sound is
listened.
Watch Test
• Is not done now but had
been very popular
before the invent of
audiometers. It's done
by bringing a clicking
watch close to the ear
and measuring distance
at which it is heard
Speech Test
• The patient stands at a distance of 6 meters from
the examiner. The examiner says words and
gradually walks towards the patient. The distance
at which conversational & whispered voice are
heard is measured. For clinical purposes 6m is
considered normal for both conversational and
whispered speech. While performing the test
eyes of the patient are covered to prevent lip
reading, also the other ear is blocked.
Tuning Fork Tests
• Theses tests are
performed with the
tuning forks of different
frequencies such as
128,256,512 Hz
• For routine practice,
tuning fork of 512 Hz is
ideal
Tuning Fork Tests
• The clinically useful tuning forks tests include:
Rinne Test
Weber Test
Others
Rinne Test
• In this test air conduction AC
of the ear is compared with
its bone conduction BC
• A vibrating tuning fork is
places on the pt mastoid and
when he stops hearing it
brought beside the meatus.
If he still hears, AC is more
than BC
Interpretations
• Rinne test is called positive when AC is
longer and than BC. It is seen in normal
person or those having sensorineural
deafness.
• A negative Rinne test when BC > AC . Is
seen in conductive deafness
Weber Test
• In this test , a vibrating
tuning fork is placed in
the middle of the
forehead and the pt is
asked in which ear the
sound is heard.
• Normally it is heard
equally in both ear
Interpretations
• It is lateralized to the worse ear in conductive
deafness and to the better ear in sensorineural
deafness
B. Audiometric tests
Audiometry is the measurement of the sense of
hearing. An audiometer is an electronic machine
that produces pure tones, the intensity of which
can be increased or decreased in 5db steps.
A graph or audiogram is developed by this way that
shows the hearing threshold
Examination of the external ear by
Otoscope
An Otoscope .srae eht otni kool ot desu si hcihw ecived lacidem a si
gnirud ssenlli rof neercs ot sepocsoto esu sredivorp erac htlaeH
motpmys a nehw etagtisevni ot osla dna spu-kcehc raluger
srae eht sevlovni
An Otoscope consists of three parts:
The handle which contains the power for the light source.
The head which contains the light bulb and magnifying lens.
The cone which is inserted into the ear canal
Using the Otoscope
The examiner first straightens the ear canal by
pulling on the pinna , inserts the ear speculum
into the external ear. The examiner can then look
through a lens on the rear of the instrument and
see inside the ear canal.
Diseases which may be diagnosed by an otoscope
include otitis media and otitis externa, infection
of the middle and outer parts of the ear.