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Symptoms of vision loss in individuals with
Refsum disease include cataracts and
impaired night vision. Which of the following
rows identifies the structure of the eye that is
affected by cataracts and the cells that, when
damaged, result in night vision loss?
Row
A.
B.
C.
D.
Cataracts
Cornea
Lens
Lens
Cornea
Night Vision Loss
Rod cells
Rod cells
Cone cells
Cone cells
The Ear
Chapter 14.3
Structure of the Ear

When talking about the structure of the
ear, we separate parts of the ear into
three categories:
1. Outer Ear
2. Middle Ear
3. Inner Ear
Outer Ear

The outer ear is composed of two main
parts:
1. The pinna which acts as a funnel to
focus sound into:
2. The auditory canal which carries sound
to the ear drum.
Middle Ear
 The middle ear is composed of two parts:
1. The eardrum, which is known as the
tympanic membrane. This takes the
vibrations of sound waves and transfers it to:
2. The ossicles, which are small bones in the
ear. These then continue the transfer of
vibrations to the inner ear.
Ossicles

The ossicles are three
bones:
1. The hammer (malleus).
2. The anvil (incus).
3. The stirrup (stapes)
Eustachian Tube
 Sometime the pressure in the ear will be
too high or too low for the inner ear.
 To correct this, air will move through the
eustachian tube to get to the right
pressure.
 The eustachian tube connects directly to
your upper pharynx.
Inner Ear

The inner ear is made up of three
structures:
1. The semicircular canals, which provide
information about dynamic equilibrium.
2. The cochlea which contains
audioreceptors.
3. The vestibule, which moves sound
waves in and out of the cochlea as well
as provide information about static
equilibrium.
Hearing
 Sound waves that reach the ear drum
cause it to vibrate.
 These vibrations are then passed onto the
ossicles, which then magnify them.
 The ossicles then pass this vibration onto
the vestibule, through another membrane
known as the oval window.
 To prevent damage to the oval window,
muscles in the ear will disconnect the
stirrup from the oval window.
 As the oval window is
pushed in, another
membrane called the
round window gets
pushed out.
 This creates a wave
of fluid through the
cochlea, which it will
interpret as sound.
Structure of the Cochlea
 The cochlea is a coil of a single tube.
 The tube is shaped as below with the
listed structures.
Organ of Coti
 The organ of Coti lies on top of the
basilar membrane.
 As the basilar membrane vibrates, hairs
on the organ of Coti will make contact
with a second membrane.
 When this happens, it initiates an impulse
in your audioreceptors.
Detecting Frequencies
 The basilar membrane starts thicker at the
beginning of the cochlea, and gets thinner as it
goes.
 Higher frequencies, which have higher
energies, will cause the early membranes to
vibrate.
 Lower frequencies will cause the later
membranes to vibrate.
 Your brain will take where in the cochlea an
impulse starts and translate that to a specific
tone.
Equilibrium

Equilibrium is separated into two
categories:
1. Static equilibrium, which relates to
motion along one plane.
2. Dynamic equilibrium, which relates to 3
dimensional movement.
Static Equilibrium

As we learnt, the vestibule detects
static equilibrium.
 It contains two sacs:
1. The saccule which detects vertical
motion (like the Spaceshot at
Galaxyland).
2. The utricle, which detects head tilt.
 These sacks are lined with cillia (little
hairs) and filled with a gelatinous material
containing tiny stones of calcium
carbonate called otoliths.
 When the sacks shift, the otoliths will
move due to gravity.
 When they do so, they brush the cillia,
which triggers a nerve impulse.
 This is then transmitted to the cerebellum
for interpretation.
Dynamic Equilibrium
 Dynamic equilibrium is detected by the
semicircular canals.
 They operate in much the same way as
the vestibular sacs, but they respond to
rotational movement.
Homework
 Pg 458 1-2
 Pg 461 1-7, 10