Download The Ear

The
Ear
Functions of the Ear
1.
2.
Hearing
Balance
There are three parts to the Ear:
1. The Outer Ear
2. The Middle Ear
3. The Inner Ear
Anatomy of Ear
•Auditory canal
•Tympanic membrane
•Pinna
•Ossicles
•Oval window
•Round window
•Cochlea
•Organ of Corti
•Semicircular canals
•Utricle
•Saccule
•Otoliths
•Auditory nerve
•Outer/middle/inner ear
Ear Anatomy…
Anatomy of the Ear
Outer Ear
Function: To gather sound waves, causing the
ear drum to vibrate.
 Made of skin and cartilage.
 The ear flap is called the pinna.
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Outer Ear
Pinna
Ear flap (cartilage)
 Funnels sound into auditory canal
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Auditory Canal
Leads into the head
 Lined with wax secreting cells
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Tympanic Membrane (aka. Ear Drum)
End of the auditory canal
 Separates outer ear from middle ear
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Middle Ear
The Eardrum is connected to the three
smallest bones in the body:
-Malleus (hammer)
- Incus (anvil)
- Stapes (stirrup)
Together these are known as the ossicles.
Middle Ear
The bones are attached to each other by
ligaments that allow them to move back and
forth & AMPLIFY the sound!
The last ossicle, the stirrup, is attached to the
oval window.
Sound Intensity and Pitch
Sound intensity - depends on number of neurons and
frequency of firing
Pitch (hi or low note) - each hair cell responds to only
one frequency.
Ear Test
Middle Ear
The eustachian tube is located just
after the eardrum, in the middle ear.
The Eustachian tube connects to the
throat and allows for pressure
equalization on both sides of the
tympanic membrane.
How do we equalize pressure?
Size of tube compared to coin
Inner Ear
Function#1: Hearing. Converts sound vibrations
from the ossicles into nerve impulses!!!
Function #2: Balance.
 The Cochlea is the organ that is responsible for
hearing (this is the place where neurons attach).
 The Cochlea is coiled, like a snail shell.
 It is divided into scala vestibule and scala
tympani by the cochlear duct.
Cochlea – Cross Section
Inner Ear
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The cochlear duct contains the Organ of Corti
where sound receptors (four rows of hair cells)
are found.
A fluid (called endolymph) surrounds the Organ
of Corti.
The scala vestibuli and the scala tympani contain
another fluid called perilymph.
The utricle, saccule, and semicircular canals are
responsible for balance and body position
The Mechanics of Hearing
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Longitudinal sound waves travel down the auditory
canal.
Tympanic membrane vibrates.
Ossicles (malleus, incus, & stapes) move.
Stapes is connected to the oval window. When the
stapes moves, it causes this window to bulge.
The oval window bulging causes the fluid in the
outer two parts of the cochlea to move.
This puts pressure on the cochlear duct.
The Mechanics of Hearing
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The pressure waves cause the basilar membrane to
move which causes the hairs in the organ of Corti
to bend against the tectorial membrane.
As the hairs bend, the small nerves that are
connected to the base of the hairs are stimulated.
These nerve impulses are carried to the brain along
the auditory nerve.
the temporal lobe of the cerebral cortex interprets
the impulses as sound.
The Mechanics of Balance
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The utricle, saccule, and semicircular canals are
important structures for balance & are filled with
fluid and contain sensory hairs.
The utricle & saccule contain small calcium
carbonate particles called otoliths (ear stones).
Movement of the head ( along one plane –
horizontal/vertical), causes the otoliths to move in
response to gravity. These particles cause sensory
hairs to bend, triggering impulses which alert the
brain as to the position of the head.
The saccule contains sensory hairs as well
The Mechanics of Balance
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The semicircular canals contain sensory
hairs which are bent by movement in the
fluid surrounding them. One canal detects
bending forward and backward, another
detects bending left or right, and a third
detects a turning motion.
The brain then signals the appropriate
muscles to maintain balance.
Semicircular Canals
Ear Safety
Small muscles in your ears help protect your
hearing
When loud noises are around,
1.
2.
Muscles attached to the hammer (malleus)
contract and restrict intense movements.
A second muscle contracts pulling the stirrup
(stapes) away from the oval window limiting inner
ear damage.
Not effective with sudden loud noises
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This response takes time.
Sudden noise causes huge damage to inner ear,
specifically the hairs in the Organ of Corti
What structures are for hearing?