Human ear, organ of hearing and equilibrium that detects and analyzes sound by transduction (or the conversion of sound waves into electrochemical impulses) and maintains the sense of balance (equilibrium).

1. The
Human
Ear
Presented By-
Mr.Vijay Salvekar
Associate Professor
GRY Institute of Pharmacy, Borawan.

2. The human ear is divided into
three sections.

4. Major Divisions of the Ear
Peripheral Mechanism Central Mechanism
Outer
Ear
Middle
Ear
Inner
Ear
VIII
Cranial
Nerve
Brain

5. Each part of
the ear serves
a specific
purpose in the
task of
detecting and
interpreting
sound.

6. The Outer Ear
• Picture a satellite dish
that collects radio
waves.
• The outer ear is
similar!
– The curved formation on
the outside ( the pinna)
helps funnel sound down
the ear canal to the
eardrum.

7. The Middle Ear
• The middle
ear transfers
the energy
of a sound
wave by
vibrating the
three bones
found there.

8. Middle ear
• Tiny air–filled cavity in the temporal
bone contains:
Auditory ossicles (bones)
Malleus
Incus
Stapes
Openings to
Outer ear covered by tympanic membrane
Inner ear = oval and round windows
Eustachian tube connects middle ear to the
nasopharnyx for air passage (normally
closed, opens with swallowing/yawning)

9. Function of Middle Ear
• Conduction
– Conduct sound from the outer ear to the inner ear
• Protection
– Creates a barrier that protects the middle and inner areas
from foreign objects
– Middle ear muscles may provide protection from loud
sounds
• Transducer
– Converts acoustic energy to mechanical energy
– Converts mechanical energy to hydraulic energy
• Amplifier
– Transformer action of the middle ear
– only about 1/1000 of the acoustic energy in air would be
transmitted to the inner-ear fluids (about 30 dB hearing loss)

10. Middle ear functions
1. Conducts sound vibration from outer ear
to inner ear
2. Protects the inner ear by reducing the
amplitude of loud sounds
3. Eustachian tube allows equalization of
air pressure on each side of the ear drum
to avoid rupture ( high altitudes)

11. Bones of the Middle Ear
Hammer
Anvil
Stirrup
Eardrum
• These are
the smallest
bones in
your body!
• Together,
they’re
about the
size of an
orange
seed.

12. Ossicles
• Malleus
(hammer)
• Incus
(anvil)
• Stapes
(stirrup)
smallest bone
of the body

13. • Malleus (hammer) – one of the middle ear
ossicles
– 3 parts
• Umbo, manubrium short process, may show
through the drum
– Lymphatic drainage of the external ear flows
into
• Parotid, mastoid, superficial cervical nodes

14. How Sound Travels in the
Middle Ear
• When sound waves
reach the middle ear,
they cause the
eardrum to vibrate.
• This vibration then
causes the three
bones to vibrate.
• These vibrations are
transformed into
longitudinal/pressure
waves in the middle
ear.

15. The
Inner
Ear
• Two main parts:
– Cochlea
– Auditory Nerve
– Semicircular canals

16. Function of Inner Ear
• Converts mechanical
sound waves to neural
impulses that can be
recognized by the brain
for:
– Hearing
– Balance

17. Inner Ear
• Contains the Bony Labyrinth which holds
the sensory organs for hearing and
equilibrium
1. Vestibule
2. Semicircular canals
3. Cochlea (contains the central hearing
apparatus)

18. Inner ear
Two compartments:
(а) Bony labyrinth and
(b) Membraneous labyrinth.
Bony labyrinth:
 complex cavity in dense
bone
Parts of the bony
labyrinth:
a.Vestibulum.
b. Semicircular canals.
c.Cochlea.

21. The Cochlea
• Coiled like a snail
shell
• Contains
approximately
300,000 hair cells
• Is filled with
fluid, through
which sound can
travel easily.

22. Cochlear Hair Cells
• These tiny
hairs bend
because of
the
vibrations
caused by
the sound
waves.

23. Cochlear Hair Cells in Action

24. Bony labyrinth.
Labyrinthus osseus
Vestibulum and semicircular canals

25. Vestibulum
Two walls: External and internal.
External wall has
• Fenestra vestibuli.
Internal wall has:
•Recessus ellipticus
•Recessus sphericus
•Recessus cochlearis
•Maculae cribrosae superior,
medius, inferior

26. Openings into vestibulum
a. Fenestra vestibuli.
b. Fenestra cochleae.
c. Openings (5) of the semicircular canals
d. Aqueductus vestibuli

27. 3: anterior, posterior and lateral.
Have ampulla and crus.
Semicircular canals

28. The Auditory Nerve
• The tiny hair cells
of the cochlea are
set in motion by
vibrations
• The vibrations
stimulate tiny
nerve cells.
• The nerve cells
then send signals
along the auditory
nerve to the brain.

29. Function of hearing
• 3 levels
1. Peripheral – ear transmits sound and
converts its vibrations into electrical
impulses that can be analyzed by the brain.
The electrical impulses are conducted by the
auditory process of cranial nerve VIII
(Acoustic) to the brain stem
1. Amplitude=loudness
2. Frequency=pitch

30. • Sound waves cause the eardrum to
vibrate
• Vibrations travel via the ossicles thru the
oval window, the cochlea and are
scattered against the round window
• The basilar membrane of the cochlea
contain the organ of Corti receptor hair
cells that translate the vibrations to electric
impulses
• The impulses go to the brainstem via
Acoustic nerve (VIII)

31. 2. Brain stem – function is binaural
interaction – permits identification of
sound and locating the direction of a
sound in space. The acoustic nerve
(Cranial nerve VIII) sends signals from
each ear to both sides of the brain stem.
Brainstem is sensitive to intensity &
timing from the ears depending on head
position

32. 3. Cerebral cortex – interprets the meaning
of the sound and begins the appropriate
response

33. Pathways of hearing
1. Air conduction (AC)– normal pathway of
hearing, the most efficient
2. Bone conduction (BC)– bones of the
skull vibrate and transmit vibrations to
the inner ear and acoustic nerve

35. A sound is
not
actually
heard until
the brain
receives
and
processes
these
signals.

36. Let’s start at the
very beginning…
• http://www.youtube.com/watch?v=CSO7
65hyxrc

37. Put the following steps in order:
A. The stirrup moves back and forth,
creating pressure waves in the
cochlea.
B. The bones of the middle ear
(hammer, anvil, & stirrup) vibrate.
C. Hair cells send an electrical
impulse through the auditory
nerve.
D. The outer part of the ear (the
pinna) "catches" the sound waves.
E. Sound waves vibrate the eardrum
F. The brain receives an electrical
impulse and interprets it as sound.
G. Tiny hair cells in the cochlea move
as the waves pass.
H. The sound waves travel into the
ear canal.
D
H
E
B
A
G
C
F