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Special
Senses
Chapter 12
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Introduction

Special senses
 Sensory receptors
located in head




Nose – smell
Tongue – taste
Eyes – vision
Ears – hearing
and equilibrium
Touch is a
generalized sense

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35-3
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How do senses work?





Receptors collect information
Stimulate neurons
Information is sent to the brain
The cerebral cortex integrates the information
with that from other senses
Forms a perception (a person’s particular view of
the stimulus)
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Receptor Structure
Receptors are structured in two basic ways:
 Nerve endings
 Cells which are associated with nerve
endings
 When these are stimulated, they produce
graded potentials. If they hit threshold, nerve
fires.

© 2009 The McGraw-Hill Companies, Inc. All rights reserved
The Ear
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
The Ear and the Senses of Hearing
and Equilibrium: Structures
External Ear
 Auricle
(pinna)
 Collects
 External
sound waves
auditory canal
 Guides
sound wave to
tympanic membrane
Ear
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The Ear and the Senses of
Hearing and Equilibrium:
Structures (cont.)
The Middle Ear

Tympanic membrane




Concave shaped membrane
Separates external canal
and middle ear
Vibrates when sound hits it
Ear ossicles

Malleus, Incus, Stapes

Ossicles vibrate in
response to vibration of
tympanic membrane
 Tympanic

Cavity
Surrounds ossicles
 Eustachian
 Connects
tube
middle ear to
throat
 Equalizes pressure on
eardrum
 Oval
window
 Separates
inner ear
middle ear from
Ear
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Middle Ear Diagram
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The Ear and the Senses of
Hearing and Equilibrium:
Structures (cont.)
Inner Ear
Labyrinth of communicating chambers
 Semicircular canals (3): detect
balance of the body
 Vestibule: central part of labyrinth;
equilibrium
 Cochlea: coiled canal ofdense bone
tissue of the skull; shaped like a snail;
 Filled with two fluids (endolymph
and perilymph).
 The Organ of Corti is the sensory
receptor inside the cochlea which
holds the hair cells, the nerve
receptors for hearing.
Ear
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Ear Wax




Cerumen; naturally produced by your body
Produced in sebaceous and modified apocrine
glands of the ear
Coats the ear canal to moisturize it, fight off
infection, keep dust, dirt, and other debris from
getting inside ear
20 to 50 percent fat
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The Ear and the Senses of
Hearing and Equilibrium:
35-13
Hearing Process







Sound waves collected through
external ear canal
Waves cause tympanic membrane
to vibrate
Ossicles amplify vibrations
The mechanical energy from movement of the middle ear
bones pushes in a membrane (the oval window) in the cochlea.
This force moves the cochlea's fluids that, in turn, stimulate tiny
hair cells.
Movement of hairs lining cochlea are converted into nerve
impulses
Impulses are transmitted by auditory nerve to the brain for
interpretation
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The Ear and the Senses of
Hearing and Equilibrium:
35-14
Hearing Process (cont.)

Bone conduction
 Alternative
pathway
 Bypasses external and
middle ear directly to
inner
 Useful in determining
cause of hearing problem
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35-15
Equilibrium
Position of Body/Movement




Motion of the body is detected in the semicircular canals



Above the cochlea are two interconnecting chambers filled with
endolymph, the sacculus and utriculus.
On their inner surface are patches of hair cells to which are attached
thousands of tiny spheres of calcium carbonate (CaCO3).
Gravity pulls these downward. As the head is oriented in different
directions, these ear stones (otoliths) shift their position. Impulses
initiated in the hair cells are sent back to the brain.
Whenever the head is moved, the fluid within the canals lags; this
stimulates the hair cells to send impulses back to the brain.
When the hair cells send messages that are incongruent with what the
eyes are seeing and our body is feeling, as may occur in a boat or aircraft
during rough weather, motion sickness can result.
Some people also suffer severe dizziness because otoliths have
become dislodged from their utriculus (following a blow to the
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
head) and settled in a semicircular canal.
35-16
How to Recognize Hearing
Problems in Children

Guidelines
 Infants
to 4 months
 Startled
by loud noises
 Recognize mother’s voice
4
to 8 months
 Regularly
follow sounds
 Babble at people
8
to 12 months
 Respond
to the sound their name
 Respond to “no”
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The Aging Ear






External ear larger / earlobe
longer
Cerumen dryer and prone to
impaction
Ear canal narrower
Eardrum shrinks and appears dull
and gray
Ossicles do not move as freely
Semicircular canals less sensitive
to changes in position – affects
balance
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Hearing Loss
Symptom of a disease, not a normal part of aging
Conductive hearing loss


Interruption in
transmission to inner ear
Causes
 Obstruction
of ear canal
 Infection of middle ear
 Reduced movement of
stirrup
Sensorineural hearing loss


Sound waves not
perceived by brain as
sound
Causes
 Hereditary
 Repeated
exposure to loud
noises / viral infections
 Side effect of medication
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Hearing and Diagnostic Tests

Hearing tests
 Tuning
forks – differentiate between types of loss
 Audiometer – measures hearing acuity

Diagnostic testing
 Tympanometry
 Measures
the ability of
the eardrums to move
 Detects diseases and
abnormalities of the
middle ear
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“Cauliflower Ear”




Cauliflower ear is medically known as
an auricular hematoma.
The external ear is made of cartilage and it
is the shape of the cartilage that gives the
ear its distinctive shell-like shape. The
cartilage is lined by perichondrium, a tight
layer of connective tissue.
Auricular hematoma occurs when the ear
cartilage is injured
Trauma results in fluid or blood collecting
between the perichondrium and the
cartilage. This blood or fluid can become
permanent and scarred, resulting in the
appearance of cauliflower ear.
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Olfaction – Sense of
Smell

Olfactory epithelium in roof of
nasal cavity
 Pseudostratified columnar
epithelium
 Has millions of bipolar neurons =
olfactory receptor cells



Only neurons undergoing replacement
throughout adult life
Olfactory cilia bind odor molecules
 Mucus captures & dissolves odor
molecules
Each receptor cell has an axon – the
cells are bundled into “filaments”
of olfactory nerve
 Penetrate plate of ethmoid bone &
enter olfactory bulb
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Olfaction!
35-22
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35-23
Olfaction

Olfactory receptors
 Chemoreceptors
– respond to changes in chemical
concentrations
 Chemicals
must be dissolved in mucus
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Day 2 Taste
Chapter 12 – Special Senses
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
Olfaction
Smell sensation
Activation of smell receptors 
information sent to olfactory nerves
that send the information along
olfactory bulbs and tracts
to different areas of the cerebrum;
cerebrum interprets the information as a
particular type of smell
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35-26
Nose and Sense of Smell (cont.)

Sensory Adaptation
 Chemical(s)
can stimulate receptors for limited
amounts of time
 Chemoreceptors fatigue and stop responding to
chemical
 Result = no longer smell odor
© 2009 The McGraw-Hill Companies, Inc. All rights reserved
The Tongue…

The tongue is a muscular organ in the
mouth.
 Covered with moist, pink tissue called mucosa.
 Tiny bumps called papillae give the tongue its


rough texture.
Thousands of taste buds (receptor cells)
cover the surfaces of the papillae. Taste buds are
collections of nerve-like cells that connect to
nerves running into the brain.
The tongue is anchored to the mouth by
webs of tough tissue and mucosa.



The tether holding down the front of the tongue is
called the frenum.
In the back of the mouth, the tongue is anchored
into the hyoid bone.
The tongue is vital for chewing and swallowing
food, as well©as
for
2009
Thespeech.
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Tongue and Sense of
Taste



Taste buds: detect chemicals dissolved in saliva from
food in the mouth and throat (chemoreceptors)
 Taste buds send their sensory information through
neurons to the gustatory center of the brain.
The average person has around 10,000 taste buds in
their mouth and throat, although the number of taste
buds peaks in early childhood and declines throughout
our lives.
Tongue
Location
 Papillae
of the tongue
 Roof of mouth
} fewer than on tongue
 Walls of throat
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35-29
Papillae Types

Foliate papillae: these are
ridges and grooves towards the
posterior part of the tongue
found at the lateral borders.

Fungiform papillae: small, on
entire surface of tongue

Vallate papillae: inverted “V”
near back of tongue

Filiform papillae: these are
thin, long papillae "V“
shaped cones that don't contain
taste buds but are the most
numerous. These papillae are
mechanical and not involved in
gustation
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Taste Buds
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35-31
Tongue Maps…
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Tongue and Sense of Taste (cont.)

Taste sensation
4

 5th
basic taste
 Glutamic acid
primary
 Sweet
 Sour
 Salty
 Bitter
Umami

Spicy foods
 Activate
pain
receptors
 Interpreted by brain
as “spicy”
Tongue
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Tongue and Sense of Taste
(cont.)
Taste sensation
Activation of
taste cells
Cranial
nerves
Gustatory cortex of cerebrum
interprets information
© 2009 The McGraw-Hill Companies, Inc. All rights reserved