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Essentials of Human Anatomy & Physiology
Seventh Edition
Elaine N. Marieb
Chapter 8
Special Senses
Slides 8.1 – 8.54
Lecture Slides in PowerPoint by Jerry L. Cook
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
The Senses
 General senses of touch
 Temperature
 Pressure
 Pain
 Special senses
 Smell
 Taste
 Sight
 Hearing
 Equilibrium
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•Special sense
receptors are either
large, complex
sensory organs
(eyes and ears) or
localized clusters or
receptors (taste
buds and olfactory
epithelium)
Slide 8.2
The Eye and Vision
 70 percent of all sensory receptors are
in the eyes
 Each eye has over a million nerve fibers
 Protection for the eye
 Most of the eye is enclosed in a bony orbit
 A cushion of fat surrounds most of the eye
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Slide 8.3
Accessory Structures of the Eye
 Eyelids
 Eyelashes
 Meibomian glands
– modified
sebaceous
glands
produce an
oily secretion
to lubricate
the eye
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Figure 8.1b
Slide 8.4
Accessory Structures of the Eye
 Ciliary glands – modified sweat glands
between the eyelashes
 Conjunctiva
 Membrane that
lines the eyelids
 Connects to the
surface of the eye
 Secretes mucus
to lubricate the eye
Figure 8.1b
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Slide 8.5
Accessory Structures of the Eye
 Lacrimal
apparatus
 Lacrimal gland –
produces lacrimal
fluid
 Lacrimal canals –
drains lacrimal
fluid from eyes
Figure 8.1a
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Slide 8.6
Accessory Structures of the Eye
 Lacrimal sac –
provides passage
of lacrimal fluid
towards nasal
cavity
 Nasolacrimal duct
– empties lacrimal
fluid into the nasal
cavity
Figure 8.1a
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Slide 8.7
Function of the Lacrimal Apparatus
 Properties of lacrimal fluid
 Dilute salt solution (tears)
 Contains antibodies and lysozyme
 Protects, moistens, and lubricates the
eye
 Empties into the nasal cavity
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Slide 8.8
Extrinsic (External) Eye Muscles
 Muscles attach to the outer surface of the
eye
 Produce gross eye movements and make it
possible to follow moving objects
Figure 8.2
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Slide 8.9
Structure of the Eye
 The wall is composed of three tunics – coats
while the interior is filled with fluids called humors
 Fibrous tunic (sclera)–
outside layer
 Choroid –
middle
layer
 Sensory
tunic –
inside
layer
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Figure 8.3a
Slide 8.10
The Fibrous Tunic
 Sclera
 White connective tissue layer
 Seen anteriorly as the “white of the eye”
 Cornea
 Transparent, central anterior portion
 Allows for light to pass through
 Repairs itself easily
 The only human tissue that can be transplanted
without fear of rejection – no blood vessels
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Slide 8.11
Choroid Layer
 Blood-rich nutritive tunic
 Dark pigment prevents light from scattering
inside the eye
 Modified interiorly into two structures
 Ciliary body – smooth muscle to which the lends
is attached
 Iris
 Pigmented layer that gives eye color
 Pupil – rounded opening in the iris for light to
enter
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Slide 8.12
Sensory Tunic (Retina)
 Contains receptor cells (photoreceptors)
 Rods
 Cones
 Signals pass from photoreceptors via a
two-neuron chain
 Bipolar neurons
 Ganglion cells
 Signals leave the retina toward the brain
through the optic nerve
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Slide 8.13
Neurons of the Retina
Figure 8.4
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Slide 8.14
Neurons of the Retina and Vision
 Rods
 Most are found towards the edges of the
retina
 Allow dim light vision and peripheral vision
 Perception is all in gray tones
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Slide 8.15
Neurons of the Retina and Vision
 Cones
 Allow for detailed color vision in bright light
 Densest in the center of the retina
 Fovea centralis – area of the retina with
only cones – lateral to each blind spot
 No photoreceptor cells are at the optic
disk, or blind spot – where the optic
nerve leaves the eyeball
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Slide 8.16
Cone Sensitivity
 There are three types of
cones
 Different cones are
sensitive to different
wavelengths
 Color blindness is the result
of lack of one cone type
Figure 8.6
 Impulses received at the
same time are interpreted
as intermediate colors
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Slide 8.17
Lens
 Biconvex crystal-like structure
 Held in place by a suspensory ligament
attached to the ciliary body
Figure 8.3a
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Slide 8.18
Internal Eye Chamber Fluids
 Aqueous humor
 Watery fluid found in chamber between the
lens and cornea
 Similar to blood plasma
 Helps maintain intraocular pressure
 Provides nutrients for the lens and cornea
 Reabsorbed into venous blood through the
canal of Schlemm
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Slide 8.19
Internal Eye Chamber Fluids
 Vitreous humor
 Gel-like substance behind the lens
 Keeps the eye from collapsing inward by
reinforcing it internally
 Lasts a lifetime and is not replaced
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Slide 8.20
Internal Eye Chamber Fluids
 Cataracts form when the
lens becomes increasingly
hard and opaque over time
requiring a transplant or
special glasses
 Glaucoma results when the drainage of
aqueous humor is blocked and pressure
within the eye increases dramatically and
compresses the delicate retina and optic
nerve causing pain and blindness
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Slide 8.21
Lens Accommodation
 Light must be focused
to a point on the retina
for optimal vision –
done by the lens
 The resting eye is set
for distance vision
(over 20 ft away)
 The lens must change
shape to focus for
closer objects –
accommodation
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Figure 8.9
Slide 8.22
Images Formed on the Retina
Figure 8.10
•Real image (reversed left to right, and
upside down) formed on the retina
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Slide 8.23
Visual Pathway
 Photoreceptors of
the retina
 Optic nerve
 Optic nerve crosses
at the optic chiasma
to the opposite side
 Fiber tracts that
result are the optic
tracts
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Figure 8.11
Slide 8.24
Visual Pathway
 Optic tracts contains fibers
from the lateral side of the
eye on the same side and
the medial side of the
opposite eye
 The optic tract fibers
synapse with neurons in
the thalamus, whose axons
form optic radiation
 Visual cortex of the
occipital lobe
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Figure 8.11
Slide 8.25
Eye Reflexes
 Internal muscles are controlled by the
autonomic nervous system
 Bright light causes pupils to constrict through
action of radial and ciliary muscles –
photopupillary reflex
 Viewing close objects causes accommodation
– accommodation pupillary reflex
 External muscles control eye movement to
follow objects
 Viewing close objects causes convergence
(eyes moving medially (toward nose))
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Slide 8.26
The Ear
 Houses two senses
 Hearing
 Equilibrium (balance)
 Receptors are mechanoreceptors –
respond to physical forces
 Although these two sense organs are
housed together in the ear, their receptors
respond to different stimuli and are
activated independently
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 8.27
Anatomy of the Ear
 The ear is divided into
three areas
 Outer (external)
ear
 Middle
ear
 Inner (internal)
ear
Figure 8.12
 Outer and middle ear structures involved in
hearing only while inner ear functions in both
equilibrium and hearing
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Slide 8.28
The External Ear
 Structures of
the external ear
 Pinna (auricle) –
the ear
 External
auditory canal
Figure 8.12
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Slide 8.29
The External Auditory Canal
 Narrow chamber in the temporal bone
 Lined with skin
 Ceruminous (wax) glands are present
that secrete earwax – cerumen
 Ends at the tympanic membrane
(eardrum) where sound waves hit and
cause vibrations
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Slide 8.30
The Middle Ear or Tympanic Cavity
 Air-filled cavity within the temporal bone
 Two tubes are associated with the inner ear
– the oval window and the inferior, membranecovered round window
 The opening from the auditory canal is
covered by the tympanic membrane
 The auditory tube connecting the middle ear
with the throat
 Allows for equalizing pressure during yawning
or swallowing – This tube is otherwise
collapsed
Slide 8.31
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Bones of the Tympanic Cavity
 Three bones span
the cavity – the
ossicles
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrup)
Figure 8.12
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Slide 8.32
Bones of the Tympanic Cavity
 Vibrations from
eardrum move
the malleus
 These bones
transfer sound
to the inner ear
Figure 8.12
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Slide 8.33
Inner Ear or Bony Labrynth
 A maze of bony chambers within the temporal
bone called the osseous or bony labyrinth
 Cochlea
 Vestibule
 Semicircular
canals
 Filled with a plasma-like fluid called perilymph
 Inside is a membranous labyrinth that contains
a thicker fluid called endolymph
Figure 8.12
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Slide 8.34
Organs of Hearing
 Organ of Corti
 Located within the cochlea
 Receptors = hair cells on the basilar
membrane – hearing receptors
 Gel-like tectorial membrane is capable of
bending hair cells
 Cochlear nerve attached to hair cells
transmits nerve impulses to auditory cortex
on temporal lobe
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Slide 8.35
Organs of Hearing
Figure 8.13
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Slide 8.36
Mechanisms of Hearing
 Vibrations from sound waves move
tectorial membrane
 Hair cells are bent by the membrane
 An action potential starts in the cochlear
nerve
 Continued stimulation can lead to
adaptation – stop responding to those
sounds
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Slide 8.37
Mechanisms of Hearing
Figure 8.14
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Slide 8.38
Organs of Equilibrium
 Receptor cells are in two structures
 Vestibule
 Semicircular canals
Figure 8.16a, b
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Slide 8.39
Organs of Equilibrium
 Equilibrium has two functional parts
 Static equilibrium
 Dynamic equilibrium
Figure 8.16a, b
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Slide 8.40
Static Equilibrium
 Maculae – receptors in the vestibule
 Report on the position of the head with respect to
gravity – help determine up from down
 Send information via the vestibular nerve
 Anatomy of the maculae
 Hair cells are embedded in the otolithic membrane
 Otoliths (tiny stones) float in a gel around the hair
cells
 Movements cause otoliths to bend the hair cells
which send impulses along the vestibular nerve to
the cerebellum
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Slide 8.41
Function of Maculae
Figure 8.15
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Slide 8.42
Dynamic Equilibrium
 Crista ampullaris –
receptors in the
semicircular canals
 Tuft of hair cells
 Cupula (gelatinous cap)
covers the hair cells
Figure 8.16c
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Slide 8.43
Dynamic Equilibrium
 Receptors respond to angular or rotatory
movements of the head
 Action of angular head
movements
 The cupula stimulates the
hair cells – gelatinous cap
 An impulse is sent via the
vestibular nerve to the cerebellum
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Figure 8.16c
Slide 8.44
Chemical Senses – Taste and Smell
 Both senses use chemoreceptors
 Stimulated by chemicals in solution
 Taste has four types of receptors
 Smell can differentiate a large range of
chemicals
 Both senses complement each other
and respond to many of the same
stimuli
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Slide 8.45
Olfaction – The Sense of Smell
 Olfactory receptors are in the roof of the
nasal cavity
 Neurons with long cilia – olfactory hairs
 Chemicals must be dissolved in mucus for
detection
 Impulses are transmitted via the olfactory
filaments which makes up the olfactory nerve
 Interpretation of smells is made in the
olfactory cortex
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Slide 8.46
Olfactory Epithelium
Figure 8.17
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Slide 8.47
The Sense of Taste
 Taste buds
house the
receptor
organs
 Location of
taste buds
 Most are on
the tongue
 Soft palate
 Inner cheeks
Figure 8.18a, b
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Slide 8.48
The Tongue and Taste
 The dorsal tongue is covered with
projections called papillae
 Filiform papillae – sharp with no taste buds
 Fungiform papillae – rounded with taste
buds
 Circumvallate papillae – large papillae with
taste buds
 Taste buds are found on the sides of
papillae
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Slide 8.49
Structure of Taste Buds
 The specific cells that respond to chemical
dissolved in saliva are epithelial cells Gustatory cells are the receptors
 Surrounded by supporting cells in the taste
bud
 Have gustatory hairs (long microvilli)
 Hairs are stimulated by chemicals dissolved in
saliva
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Slide 8.50
Structure of Taste Buds
 Impulses are carried to the gustatory
complex by several cranial nerves
because taste buds are found in different
areas
 Facial nerve – anterior tongue specifically
 Glossopharyngeal nerve
 Vagus nerve
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Slide 8.51
Anatomy of Taste Buds
Figure 8.18
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Slide 8.52
Taste Sensations
 Sweet receptors
 Sugars
•May
respond
to
the
OH
 Saccharine
 Some amino acids
 Sour receptors
 Acids
 May respond to the H+
 Bitter receptors
 Alkaloids
 Salty receptors
 Metal ions in solution
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Slide 8.53
Developmental Aspects of the
Special Senses
 Formed early in embryonic development
 Eyes are outgrowths of the brain
 All special senses are functional at birth
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Slide 8.54