3. What is Hearing ???
Generally hearing is the sensation of sound.
Hearing or the auditory perception is the
ability to perceive sounds by detecting
vibrations, changes in the pressure of the
surrounding medium through time, through
an organ such as the ear.
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4. Introduction:
•Ear is the main organ for hearing. Sound wave enters
the outer ear and cause the ear drum to vibrate.
•These vibrations pass along the middle ear via three
small bones known as the ossicles.
• The ossicles amplify the vibrations and transmit them
on to cochlea in the inner ear.
•Hair cells in the cochlea moves in the response to the
vibrations and send electrical signals along the auditory
nerve to the brain which converts the vibrations into
sound we can understand.
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6. Ear:
The ear is the organ of the hearing as well as
balancing anatomically.
The ear is divided into three parts.
1. The external ear
2. The middle ear
3. The inner ear
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7. The external ear:
•The external ear is formed by 2 parts
i.e
a)Auricle or pinna
b)The external acoustic meatus
c)Tympanic membrane
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8. Role of external ear in hearing
The pinna:
It is the first part of ear that
reacts with sound .The function
of pinna is to act like funnel and
assist in directing the sound
further into the ear.
The pinna is essential due to the
difference in pressure inside and
outside the ear.
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9. The ear cannel:
•Once the sound waves have
passed the pinna, they move two
to three centimetres into the
auditory canal before hitting the
eardrum, also known as tympanic
membrane.
•The function of ear canal is to
transmit sound from pinna to the
eardrum.
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10. CONTINUE…
•THE EARDRUM:
Ear drum is the end point of the external ear.
The eardrum is extremely sensitive and
pressure from sound wave makes the ear drum
vibrate.
The auditory canal is slightly curved in order to
protect the eardrum and also it automatically
amplifies low and less penetrating sound of
human voice.
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11. The middle ear
• Middle ear or tympanic
cavity is a small , narrow,
irregular compressed
chamber situated within
the temporal bone.
• It is separated from
external auditory meatus
by tympanic membrane.
• Middle ear consists of the
following structures.
a.Auditory ossicles
b.Auditory muscles
c. Eustachian tube
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12. Role of middle ear in hearing
• The middle ear is the part of ear between the
eardrum and the oval window. The middle ear
transmit the sound from the outer ear to inner ear.
Bones of the middle ear:
The vibrated waves from the eardrum are transmitted
further into the ear via three bones .they are:
a. Malleus
b. Incus
c. Stapes
These three bones forms a kind of bridge and is
connected to the oval window.
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13. CONTINUE…
THE OVAL WINDOW:
The main function of the oval window is to
amplify the sound before they move to inner
ear.
THE ROUND WINDOW:
It allows fluid in the cochlea to move
THE EUSTACHIAN TUBE:
The function of eustachian tube is to equalise
the air pressure inside and outside the ear.
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14. The inner ear:
• Internal ear is a membranous
structure enclosed by a bony
labyrinth in petrous part of temporal
bone
• It consists the sense organs of hearing
and equilibrium
• Cochlea is the sense organ for hearing
• Organ of corti which is the receptor
organ for hearing is situated in
cochlea inside inner ear
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15. ROLE OF INNER EAR IN HEARING
• The inner ear is the innermost part of the ear which consists of the
cochlea, the vestibular and auditory nerve.
COCHLEA:
The cochlea resembles a snail shail which is filled with fluid. When the fluid
moves inside the cochlea , thousands of microscopic hair fibres comes in
motion. The hair fibres send auditory nerve which is connected to the
auditory center of the brain.
In cochlea sound waves are transformed into electrical impulses which are
sent to brains
The brain then translets the impulses into sound that we know and
understand
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16. Physiology of Hearing:
Physiology of hearing can be discussed as
follows.
1. Stimuli
2. Conduction of sound waves
3. Transduction of sound waves
4. Neural transmission of signals
5. Encoding of signals
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17. Stimuli or sound waves:
Stimuli for the receptor of hearing are sound waves.
Sound is a form of energy produced by a vibrating
object.
Physical properties of sound:
range: range of human hearing is appox 20-20000
hertz.
Pitch: is the subjective produce by frequency of
sound. Higher the frequency greater the pitch.
Frequency: number of waves per second.
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18. CONDUCTIONS OF SOUND WAVE:
Role of external ear:
• Pinna collects and reflects the sound waves into the external auditory
meatus.
• External auditory meatus conducts the sound waves to tympanic. Its s-
shaped course helps in amplyfing the sound.
Role of middle ear:
• Conduction of sound stimulus by tympanic membrane to ear ossicles.
Tympanic membrane vibrations are transmitted
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19. Transduction of sound wave:
• Transduction of mechanical sound wave into electricl
signals occurs in the organ of corti of inner ear
a. Sound wave entering the inner ear spread along the
scala vestibulei as traveling wave. As the sound energy
passes from scala vestibuli to scala tympani, it causes
the basilar membrane to vibrate.
b. The up and down moments of the basilar membrane in
turn causes the organ of corti to vibrate up and down.
The bending of stereocilla stimulates the hair cells
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20. NEURAL TRANSMISSION OF SIGNALS:
The electrical signals from hair cells are transmitted through
a complex auditory pathway to the auditory cortex.
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21. Neural processing of auditory information:
•In the auditory cortex the sound wave in the form
of nerve impulse is processed and perceived. Neural
processing of auditory information involves :
1. Encoding of frequency ( pitch determination)
2. Encoding of intensity (determination of loudness)
3. Feature detection and
4. Localization of sound in space
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22. CONTINUE….
• In this section the wave frequency are converted
into electrical signals . Hair cells present in the
cochlea of the inner ear is responsible for this. The
electrical singals are carried to the auditory center in
the brain through vestibulocochlear nerve.it is a
cranial nerve which enters into the brainstem just
beneath the cerebellum.
• The auditory center in the brain converts the wave
signals into sound that we can understand.
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24. Auditory nervous pathways
The auditory pathways conveys the special of
hearing. Information travels from the receptor
in the organ of corti of the inner ear to the
central nervous system carried by the
vestibulocochlear nerve.
This pathway ultimately reaches the primary
auditory cortex for conscious perception in
auddition.
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25. CONCLUSION:
1. The pinna funnels sound wave into the ear canal. The sound
waves will travel to the tympanic membrane.
2. The mallus will receive the sound and amplify the vibrations
across the ossicles in the middle ear.
3. The osicles push the sound waves with greater vibrations to the
oval window.
4. These vibrations in the oval window will generate fluid within
the vestibular duct to move the waves into cochlear duct.
5. These wave cause tectorial membrane to bounce. And also
movement of basilar membrane cause hair cells to bend
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26. Continue…
6. When the hair cell bend, ion channel open and
release neurotransmitters into the synapse with the
sensory neurone. Causing it to change the rate of AP
firing to the brain via cochlear nerve.
7. The cochlear nerve carries the impulses to primary
auditory neurons in the medulla .
8. Then the info will go to the secondary neurons in
the midbrain and thalamus before projecting into
the auditory cortex
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27. REFRESENCES
•1. Tortora GJ and Derrickson BH (2009), Principles of
Anatomy and Physiology (12th Ed.), Danvers and Wiley
India Pvt. Ltd, 332-336.
•2. KC T and Gautam R(2014), Essential Text Book of
Anatomy and Physiology (1st Ed.),Samiksha Publication
Pvt. Ltd, 191-194.
•3. URL: http://drfasih.com/mechanism-of-hearing/
(Assessed on July 09, 2018).
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