Used with permission from Pearson for Clay Virtual Academy. Copyright Pearson, Inc.

1. PowerPoint® Lecture Slide Presentation
by Patty Bostwick-Taylor,
Florence-Darlington Technical College
Special Senses
8
PART A
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2. The Senses
 Special senses
 Smell
 Taste
 Sight
 Hearing
 Equilibrium
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3. Structure of the Eye
Figure 8.4a
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4. Structure of the Eye: The Fibrous Layer
 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
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5. Structure of the Eye: Vascular Layer
 Choroid is a blood-rich nutritive layer in the
posterior of the eye
 Pigment prevents light from scattering
 Modified anteriorly into two structures
 Ciliary body—smooth muscle attached to lens
 Iris—regulates amount of light entering eye
 Pigmented layer that gives eye color
 Pupil—rounded opening in the iris
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6. Structure of the Eye: Sensory Layer
 Retina contains two layers
 Outer pigmented layer
 Inner neural layer
 Contains receptor cells (photoreceptors)
 Rods
 Cones
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7. Structure of the Eye: Sensory Layer
 Signals leave the retina toward the brain through
the optic nerve
 Optic disc (blind spot) is where the optic nerve
leaves the eyeball
 Cannot see images focused on the optic disc
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8. Structure of the Eye: Sensory Layer
Figure 8.5a
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9. Structure of the Eye: Sensory Layer
 Neurons of the retina and vision
 Rods
 Most are found towards the edges of the
retina
 Allow dim light vision and peripheral
vision
 All perception is in gray tones
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10. Structure of the Eye: Sensory Layer
 Neurons of the retina and vision
 Cones
 Allow for detailed color vision
 Densest in the center of the retina
 Fovea centralis—area of the retina with
only cones
 No photoreceptor cells are at the optic disc, or
blind spot
PLAY The Eye: The Retina
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11. Structure of the Eye: Sensory Layer
 Cone sensitivity
 Three types of cones
 Different cones are sensitive to different
wavelengths
 Color blindness is the result of the lack of one
cone type
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12. Sensitivities of Cones to Different Wavelengths
Figure 8.6
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13. Lens
 Biconvex crystal-like structure
 Held in place by a suspensory ligament attached
to the ciliary body
PLAY The Eye: Lens and Retina
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14. Lens
Figure 8.4a
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15. Lens
 Cataracts result when the lens becomes hard and
opaque with age
 Vision becomes hazy and distorted
 Eventually causes blindness in affected eye
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16. Lens
Figure 8.7
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17. Two Segments, or Chambers, of the Eye
 Anterior (aqueous) segment
 Anterior to the lens
 Contains aqueous humor
 Posterior (vitreous) segment
 Posterior to the lens
 Contains vitreous humor
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18. Anterior Segment
 Aqueous humor
 Watery fluid found between lens and cornea
 Similar to blood plasma
 Helps maintain intraocular pressure
 Provides nutrients for the lens and cornea
 Reabsorbed into venous blood through the
scleral venous sinus, or canal of Schlemm
PLAY The Eye: Interior Parts of the Eye
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19. Posterior Segment
 Vitreous humor
 Gel-like substance posterior to the lens
 Prevents the eye from collapsing
 Helps maintain intraocular pressure
PLAY The Eye: Posterior Cavity
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20. Pathway of Light Through the Eye
 Light must be focused to a point on the retina for
optimal vision
 The eye is set for distance vision
(over 20 feet away)
 Accommodation—the lens must change shape to
focus on closer objects (less than 20 feet away)
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21. Pathway of Light Through the Eye
Figure 8.9
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22. Pathway of Light Through the Eye
 Image formed on the retina is a real image
 Real images are
 Reversed from left to right
 Upside down
 Smaller than the object
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23. Images Formed on the Retina
Figure 8.10
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24. A Closer Look
 Emmetropia—eye focuses images correctly on
the retina
 Myopia (nearsighted)
 Distant objects appear blurry
 Light from those objects fails to reach the
retina and are focused in front of it
 Results from an eyeball that is too long
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25. A Closer Look
 Hyperopia (farsighted)
 Near objects are blurry while distant objects
are clear
 Distant objects are focused behind the retina
 Results from an eyeball that is too short or
from a “lazy lens”
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26. A Closer Look
 Astigmatism
 Images are blurry
 Results from light focusing as lines, not
points, on the retina due to unequal
curvatures of the cornea or lens
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27. Homeostatic Imbalances of the Eyes
 Night blindness—inhibited rod function that
hinders the ability to see at night
 Color blindness—genetic conditions that result in
the inability to see certain colors
 Due to the lack of one type of cone (partial
color blindness)
 Cataracts—when lens becomes hard and opaque,
our vision becomes hazy and distorted
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28. Homeostatic Imbalances of the Eyes
 Glaucoma—can cause blindness due to
increasing pressure within the eye
 Hemianopia—loss of the same side of the visual
field of both eyes; results from damage to the
visual cortex on one side only
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29. The Ear
 Houses two senses
 Hearing
 Equilibrium (balance)
 Receptors are mechanoreceptors
 Different organs house receptors for each sense
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30. Anatomy of the Ear
 The ear is divided into three areas
 External (outer) ear
 Middle ear (tympanic cavity)
 Inner ear (bony labyrinth)
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31. Anatomy of the Ear
Figure 8.12
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32. The External Ear
 Involved in hearing only
 Structures of the external ear
 Auricle (pinna)
 External acoustic meatus (auditory canal)
 Narrow chamber in the temporal bone
 Lined with skin and ceruminous (wax)
glands
 Ends at the tympanic membrane
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33. The Middle Ear (Tympanic Cavity)
 Air-filled cavity within the temporal bone
 Only involved in the sense of hearing
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34. The Middle Ear (Tympanic Cavity)
 Two tubes are associated with the inner ear
 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
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35. Bones of the Middle Ear (Tympanic Cavity)
 Three bones (ossicles) span the cavity
 Malleus (hammer)
 Incus (anvil)
 Stapes (stirrip)
 Function
 Vibrations from eardrum move the malleus 
anvil  stirrup  inner ear
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36. Anatomy of the Ear
Figure 8.12
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37. Inner Ear or Bony Labyrinth
 Includes sense organs for hearing and balance
 A maze of bony chambers within the temporal
bone
 Cochlea
 Vestibule (static equilibrium – position of
head)
 Semicircular canals (dynamic equilibrium –
movement of head)
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38. Organs of Equilibrium
Figure 8.14a–b
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39. Mechanism of Hearing
Figure 8.16a
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40. Olfaction—The Sense of Smell
 Olfactory receptors are in the roof of the nasal
cavity
 Neurons with long cilia
 Chemicals must be dissolved in mucus for
detection
 Impulses are transmitted via the olfactory nerve
 Interpretation of smells is made in the cortex
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41. The Sense of Taste
 Taste buds house the receptor organs
 Location of taste buds
 Most are on the tongue
 Soft palate
 Cheeks
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42. Taste Buds
Figure 8.18
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43. Taste Sensations
 Sweet receptors (sugars)
 Saccharine
 Some amino acids
 Sour receptors
 Acids
 Bitter receptors
 Alkaloids
 Salty receptors
 Metal ions
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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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45. 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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