1. PowerPointÂŽ Lecture Slide Presentation
by Patty Bostwick-Taylor,
Florence-Darlington Technical College
Special Senses
8
PART A
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2. The Senses
ī§ Special senses
ī§ Smell
ī§ Taste
ī§ Sight
ī§ Hearing
ī§ 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
ī§ Sclera
ī§ White connective tissue layer
ī§ Seen anteriorly as the âwhite of the eyeâ
ī§ Cornea
ī§ Transparent, central anterior portion
ī§ Allows for light to pass through
ī§ Repairs itself easily
ī§ The only human tissue that can be
transplanted without fear of rejection
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
5. Structure of the Eye: Vascular Layer
ī§ Choroid is a blood-rich nutritive layer in the
posterior of the eye
ī§ Pigment prevents light from scattering
ī§ Modified anteriorly into two structures
ī§ Ciliary bodyâsmooth muscle attached to lens
ī§ Irisâregulates amount of light entering eye
ī§ Pigmented layer that gives eye color
ī§ Pupilârounded opening in the iris
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
6. Structure of the Eye: Sensory Layer
ī§ Retina contains two layers
ī§ Outer pigmented layer
ī§ Inner neural layer
ī§ Contains receptor cells (photoreceptors)
ī§ Rods
ī§ Cones
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
7. Structure of the Eye: Sensory Layer
ī§ Signals leave the retina toward the brain through
the optic nerve
ī§ Optic disc (blind spot) is where the optic nerve
leaves the eyeball
ī§ Cannot see images focused on the optic disc
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
8. Structure of the Eye: Sensory Layer
Figure 8.5a
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9. Structure of the Eye: Sensory Layer
ī§ Neurons of the retina and vision
ī§ Rods
ī§ Most are found towards the edges of the
retina
ī§ Allow dim light vision and peripheral
vision
ī§ All perception is in gray tones
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
10. Structure of the Eye: Sensory Layer
ī§ Neurons of the retina and vision
ī§ Cones
ī§ Allow for detailed color vision
ī§ Densest in the center of the retina
ī§ Fovea centralisâarea of the retina with
only cones
ī§ 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
ī§ Cone sensitivity
ī§ Three types of cones
ī§ Different cones are sensitive to different
wavelengths
ī§ 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
ī§ Biconvex crystal-like structure
ī§ Held in place by a suspensory ligament attached
to the ciliary body
PLAY The Eye: Lens and Retina
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15. Lens
ī§ Cataracts result when the lens becomes hard and
opaque with age
ī§ Vision becomes hazy and distorted
ī§ Eventually causes blindness in affected eye
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
17. Two Segments, or Chambers, of the Eye
ī§ Anterior (aqueous) segment
ī§ Anterior to the lens
ī§ Contains aqueous humor
ī§ Posterior (vitreous) segment
ī§ Posterior to the lens
ī§ Contains vitreous humor
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
18. Anterior Segment
ī§ Aqueous humor
ī§ Watery fluid found between lens and cornea
ī§ Similar to blood plasma
ī§ Helps maintain intraocular pressure
ī§ Provides nutrients for the lens and cornea
ī§ Reabsorbed into venous blood through the
scleral venous sinus, or canal of Schlemm
PLAY The Eye: Interior Parts of the Eye
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
19. Posterior Segment
ī§ Vitreous humor
ī§ Gel-like substance posterior to the lens
ī§ Prevents the eye from collapsing
ī§ Helps maintain intraocular pressure
PLAY The Eye: Posterior Cavity
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
20. Pathway of Light Through the Eye
ī§ Light must be focused to a point on the retina for
optimal vision
ī§ The eye is set for distance vision
(over 20 feet away)
ī§ Accommodationâthe lens must change shape to
focus on closer objects (less than 20 feet away)
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
21. Pathway of Light Through the Eye
Figure 8.9
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22. Pathway of Light Through the Eye
ī§ Image formed on the retina is a real image
ī§ Real images are
ī§ Reversed from left to right
ī§ Upside down
ī§ 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
ī§ Emmetropiaâeye focuses images correctly on
the retina
ī§ Myopia (nearsighted)
ī§ Distant objects appear blurry
ī§ Light from those objects fails to reach the
retina and are focused in front of it
ī§ Results from an eyeball that is too long
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
25. A Closer Look
ī§ Hyperopia (farsighted)
ī§ Near objects are blurry while distant objects
are clear
ī§ Distant objects are focused behind the retina
ī§ Results from an eyeball that is too short or
from a âlazy lensâ
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
26. A Closer Look
ī§ Astigmatism
ī§ Images are blurry
ī§ Results from light focusing as lines, not
points, on the retina due to unequal
curvatures of the cornea or lens
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
27. Homeostatic Imbalances of the Eyes
ī§ Night blindnessâinhibited rod function that
hinders the ability to see at night
ī§ Color blindnessâgenetic conditions that result in
the inability to see certain colors
ī§ Due to the lack of one type of cone (partial
color blindness)
ī§ Cataractsâwhen lens becomes hard and opaque,
our vision becomes hazy and distorted
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
28. Homeostatic Imbalances of the Eyes
ī§ Glaucomaâcan cause blindness due to
increasing pressure within the eye
ī§ Hemianopiaâloss of the same side of the visual
field of both eyes; results from damage to the
visual cortex on one side only
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
29. The Ear
ī§ Houses two senses
ī§ Hearing
ī§ Equilibrium (balance)
ī§ Receptors are mechanoreceptors
ī§ Different organs house receptors for each sense
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
30. Anatomy of the Ear
ī§ The ear is divided into three areas
ī§ External (outer) ear
ī§ Middle ear (tympanic cavity)
ī§ Inner ear (bony labyrinth)
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
31. Anatomy of the Ear
Figure 8.12
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32. The External Ear
ī§ Involved in hearing only
ī§ Structures of the external ear
ī§ Auricle (pinna)
ī§ External acoustic meatus (auditory canal)
ī§ Narrow chamber in the temporal bone
ī§ Lined with skin and ceruminous (wax)
glands
ī§ Ends at the tympanic membrane
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
33. The Middle Ear (Tympanic Cavity)
ī§ Air-filled cavity within the temporal bone
ī§ Only involved in the sense of hearing
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
34. The Middle Ear (Tympanic Cavity)
ī§ Two tubes are associated with the inner ear
ī§ The opening from the auditory canal is
covered by the tympanic membrane
ī§ The auditory tube connecting the middle ear
with the throat
ī§ Allows for equalizing pressure during
yawning or swallowing
ī§ This tube is otherwise collapsed
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
35. Bones of the Middle Ear (Tympanic Cavity)
ī§ Three bones (ossicles) span the cavity
ī§ Malleus (hammer)
ī§ Incus (anvil)
ī§ Stapes (stirrip)
ī§ Function
ī§ Vibrations from eardrum move the malleus ī
anvil ī stirrup ī inner ear
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
36. Anatomy of the Ear
Figure 8.12
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
37. Inner Ear or Bony Labyrinth
ī§ Includes sense organs for hearing and balance
ī§ A maze of bony chambers within the temporal
bone
ī§ Cochlea
ī§ Vestibule (static equilibrium â position of
head)
ī§ Semicircular canals (dynamic equilibrium â
movement of head)
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
38. Organs of Equilibrium
Figure 8.14aâb
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39. Mechanism of Hearing
Figure 8.16a
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
40. OlfactionâThe Sense of Smell
ī§ Olfactory receptors are in the roof of the nasal
cavity
ī§ Neurons with long cilia
ī§ Chemicals must be dissolved in mucus for
detection
ī§ Impulses are transmitted via the olfactory nerve
ī§ Interpretation of smells is made in the cortex
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
41. The Sense of Taste
ī§ Taste buds house the receptor organs
ī§ Location of taste buds
ī§ Most are on the tongue
ī§ Soft palate
ī§ Cheeks
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
43. Taste Sensations
ī§ Sweet receptors (sugars)
ī§ Saccharine
ī§ Some amino acids
ī§ Sour receptors
ī§ Acids
ī§ Bitter receptors
ī§ Alkaloids
ī§ Salty receptors
ī§ Metal ions
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
44. Chemical Senses: Taste and Smell
ī§ Both senses use chemoreceptors
ī§ Stimulated by chemicals in solution
ī§ Taste has four types of receptors
ī§ Smell can differentiate a large range of
chemicals
ī§ Both senses complement each other and respond
to many of the same stimuli
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings
45. Developmental Aspects of the Special Senses
ī§ Formed early in embryonic development
ī§ Eyes are outgrowths of the brain
ī§ All special senses are functional at birth
Copyright Š 2009 Pearson Education, Inc., publishing as Benjamin Cummings