1. © 2013 Pearson Education, Inc.
PowerPoint®
Lecture Slides
prepared by
Meg Flemming
Austin Community College
C H A P T E R 9
The General
and Special
Senses

2. © 2013 Pearson Education, Inc.
Chapter 9 Learning Outcomes
• 9-1
• Explain how the organization of receptors for the general senses
and the special senses affects their sensitivity.
• 9-2
• Identify the receptors for the general senses, and describe how
they function.
• 9-3
• Describe the sensory organs of smell, and discuss the processes
involved in olfaction.
• 9-4
• Describe the sensory organs of taste, and discuss the processes
involved in gustation.

3. © 2013 Pearson Education, Inc.
Chapter 9 Learning Outcomes
• 9-5
• Identify the internal and accessory structures of the eye, and
explain their functions.
• 9-6
• Explain how we form visual images and distinguish colors, and
discuss how the central nervous system processes visual
information.
• 9-7
• Describe the parts of the external, middle, and internal ear, and the
receptors they contain, and discuss the processes involved in the
senses of equilibrium and hearing.
• 9-8
• Describe the effects of aging on smell, taste, vision, and hearing.

4. © 2013 Pearson Education, Inc.
Sensory Receptors (9-1)
• Can be special cell processes
• Or separate cells
• Monitor conditions both inside and outside the
body

5. © 2013 Pearson Education, Inc.
Free Nerve Endings (9-1)
• The simplest receptors
• Are modified dendritic endings
• Examples:
• Touch receptors
• Pain receptors
• Heat receptors
• Taste receptors

6. © 2013 Pearson Education, Inc.
Separate Receptor Cells (9-1)
• Complex structures
• Associated with supportive cells
• Examples:
• Visual receptors in the eyes
• Auditory receptors in the ears

7. © 2013 Pearson Education, Inc.
The Receptive Field (9-1)
• The area monitored by a single receptor
• The smaller the field, the more precise the sensory
information

8. © 2013 Pearson Education, Inc.
Sensation and Perception (9-1)
• Sensation
• Occurs in the brain
• The action potential from the afferent pathway arrives in
sensory cortex
• Perception
• Awareness and interpretation of sensory input by the
integration areas of cerebral cortex

9. © 2013 Pearson Education, Inc.
Adaptation (9-1)
• A reduction in sensitivity due to a constant
stimulus
• Some sensory receptors adapt quickly (e.g.,
jumping into a cold lake)
• Some are slow to adapt or do not adapt at all, like
pain receptors

10. © 2013 Pearson Education, Inc.
General Senses (9-1)
• Temperature
• Pain
• Touch
• Pressure
• Vibration
• Proprioception (body position)
• Occur throughout the body

11. © 2013 Pearson Education, Inc.
Special Senses (9-1)
• Olfaction (smell)
• Gustation (taste)
• Vision
• Equilibrium (balance)
• Hearing
• Concentrated in the sense organs and located in
the head

12. © 2013 Pearson Education, Inc.
Figure 9-1 Receptors and Receptive Fields.
Receptive
field 1
Receptive
field 2

13. © 2013 Pearson Education, Inc.
Checkpoint (9-1)
1. What is adaptation?
2. Receptor A has a circular receptive field with a
diameter of 2.5 cm. Receptor B has a circular
receptive field 7.0 cm in diameter. Which receptor
provides more precise sensory information?
3. List the five special senses.

14. © 2013 Pearson Education, Inc.
Classes of General Sensory Receptors (9-2)
• Classified by type of stimulus that activates them
• Nociceptors respond to pain
• Thermoreceptors respond to temperature
• Mechanoreceptors respond to touch, pressure, and
body position
• Chemoreceptors respond to chemical stimuli

15. © 2013 Pearson Education, Inc.
Nociceptors (9-2)
• Free nerve endings that adapt very slowly
• Can respond to extremes of temperature,
mechanical damage, dissolved chemicals
• Fast pain transmitted to CNS through myelinated axons
• Slow pain transmitted by unmyelinated axons and is
burning or aching
• Referred pain is perception of pain in an unrelated area
of the body

16. © 2013 Pearson Education, Inc.
Liver and
gallbladder
Heart
Stomach
Small
intestine
Appendix
Colon
Ureters
Figure 9-2 Referred Pain.

17. © 2013 Pearson Education, Inc.
Thermoreceptors (9-2)
• Free nerve endings
• In dermis, skeletal muscles, liver, and hypothalamus
• Cold receptors
• More numerous than warm receptors, although there is
no known difference in structure
• They use the same pathway as pain receptors, but
thermoreceptors are adaptive

18. © 2013 Pearson Education, Inc.
Three Classes of Mechanoreceptors
1. Tactile receptors
• Touch
2. Baroreceptors
• Pressure
3. Proprioceptors
• Position

19. © 2013 Pearson Education, Inc.
Tactile Receptors (9-2)
• Include fine touch and pressure receptors and crude
touch and pressure receptors
• Six types of tactile receptors in the skin
1. Free nerve endings responding to temperature and pain
2. Root hair plexus
3. Tactile (Merkel) disc
4. Tactile (Meissner) corpuscle
5. Lamellated (pacinian) corpuscle
6. Ruffini corpuscle

20. © 2013 Pearson Education, Inc.
Free nerve
endings
Root hair
plexus
Tactile discs innervating
Merkel cells
Tactile disc
Merkel cells
Tactile corpuscle
Dermis
Dendrites
Lamellated
corpuscle
Dermis
Dendrite
Ruffini corpuscle
Sensory
nerve fiber
DendritesFree
nerve
ending
Tactile
corpuscle
Tactile disc
(innervating
Merkel cell)
Hair
Root hair
plexus
Lamellated
corpuscle
Ruffini
corpuscle
Sensory
nerves
Figure 9-3 Tactile Receptors in the Skin.

21. © 2013 Pearson Education, Inc.
Baroreceptors (9-2)
• Monitor changes in pressure in the viscera
• Adapt readily
• Found in the major blood vessels, lungs, digestive,
and urinary tracts

22. © 2013 Pearson Education, Inc.
Figure 9-4 Baroreceptors and the Regulation of Autonomic Functions.
Baroreceptors of Carotid
Sinus and Aortic Sinus
Baroreceptors of Lung
Baroreceptors of Colon
Baroreceptors of
Digestive Tract
Baroreceptors of
Bladder Wall

23. © 2013 Pearson Education, Inc.
Proprioceptors (9-2)
• Monitor position, tension in tendons and
ligaments, state of muscle contraction
• Nonadaptive and include:
• Free nerve endings that monitor joint capsule pressure,
tension, and movement
• Golgi tendon organs that monitor strain on tendons
• Muscle spindles that monitor the length of a muscle

24. © 2013 Pearson Education, Inc.
Chemoreceptors (9-2)
• Respond to chemicals in solution in body fluids
• Include CNS receptors that monitor CSF, plasma
concentrations of carbon dioxide, and pH
• Key peripheral chemoreceptors for plasma carbon
dioxide and pH are in the carotid bodies and
aortic bodies

25. © 2013 Pearson Education, Inc.
Figure 9-5 Locations and Functions of Chemoreceptors.
Chemoreceptors in and
near Respiratory Centers
of Medulla Oblongata
Trigger reflexive
adjustments in
depth and rate of
respiration
Chemoreceptors
of Carotid Bodies
Chemoreceptors
of Aortic Bodies
Trigger reflexive
adjustments in
respiratory and
cardiovascular
activity
Cranial
nerve IX
Cranial
nerve X

26. © 2013 Pearson Education, Inc.
Checkpoint (9-2)
4. List the four types of general sensory receptors,
and identify the nature of the stimulus that excites
each type.
5. Identify the three classes of mechanoreceptors.
6. What would happen if information from
proprioceptors in your legs were blocked from
reaching the CNS?

27. © 2013 Pearson Education, Inc.
Special Sense of Olfaction (9-3)
• Olfactory organs found in the nasal cavity
• Olfactory epithelium, containing olfactory
receptor cells, supporting cells, and stem cells,
lines the nasal cavity
• Olfactory glands, which are deeper, secrete
mucus
• Air is warmed and moisturized as it is inhaled

28. © 2013 Pearson Education, Inc.
Special Sense of Olfaction (9-3)
• Olfactory receptor cells
• Modified neurons with chemical receptors called
odorant-binding proteins on the cilia
• Odorants are chemicals in the air that bind to the
proteins
• Respond to over 1000 unique smells

29. © 2013 Pearson Education, Inc.
Olfactory Pathways (9-3)
• Axons projecting from the olfactory epithelium
• Bundled and pass through the cribriform plate of the
ethmoid bone and into olfactory bulb
• Olfactory tracts extend back to the olfactory cortex of
the cerebrum, the hypothalamus, and the limbic system
• Olfaction is the only sense that is NOT routed
through the thalamus

30. © 2013 Pearson Education, Inc.
Figure 9-6a The Olfactory Organs.
Olfactory Pathway to the Cerebrum
Olfactory
epithe-
lium
Olfactory
nerve
Fibers
(N I)
Olfactory
tract
Central
nervous
system
Cribriform
plate
Superior
nasal
concha
The olfactory organ on the right
side of the nasal septum.
Olfactory
bulb

31. © 2013 Pearson Education, Inc.
Figure 9-6b The Olfactory Organs.
Basal cell:
divides to
replace
worn-out
olfactory
receptor
cells
Olfactory
gland
To
olfactory
bulb
Cribriform
plate
Areolar
tissue
Olfactory
epithelium
Substance being smelled
Olfactory
nerve fibers
Developing
olfactory
receptor cell
Olfactory
receptor cell
Supporting cell
Mucous layer
Olfactory cilia:
surfaces contain
receptor proteins
An olfactory receptor is a modified neuron
with multiple cilia extending from its free
surface.

32. © 2013 Pearson Education, Inc.
Checkpoint (9-3)
7. Define olfaction.
8. How does repeated sniffing help to identify faint
odors?

33. © 2013 Pearson Education, Inc.
Special Sense of Gustation (9-4)
• Gustatory receptors
• Found in the gustatory cells of the taste buds, which
are found on the sides of the papillae
• Circumvallate papillae most numerous and on the front
2/3 of the tongue
• Gustatory cells have microvilli (taste hairs) that
extend out through the taste pore

34. © 2013 Pearson Education, Inc.
Special Sense of Gustation (9-4)
• Taste hairs respond to chemicals in solution
• Trigger a change in the membrane potential of the
taste cells
• Primary taste sensations
• Sweet, sour, bitter, salty, and umami
• Also receptors in the pharynx for water

35. © 2013 Pearson Education, Inc.
The Taste Pathway (9-4)
• Extends from the taste cell axons found in:
• Facial nerve (N VII)
• Glossopharyngeal (N IX)
• Vagus (N X)
• Fibers synapse in the medulla oblongata
• Those neurons extend into the thalamus
• Neurons project to the primary sensory cortex

36. © 2013 Pearson Education, Inc.
Water receptors
(pharynx) Umami
Taste
buds
Taste
budsSour
Bitter
Salty
Sweet
Circumvallate papilla
Taste buds LM x 280
Supporting
cell
Gustatory
cell
Taste
hairs
(microvilli)
Taste
pore
Tastes are detected by gustatory receptors within
taste buds, which form pockets along the sides of
epithelial projections called papillae.
A diagrammatic view of the structure of
a taste bud, showing gustatory
receptor cells and supporting cells.
Figure 9-7 Gustatory Receptors.

37. © 2013 Pearson Education, Inc.
Checkpoint (9-4)
9. Define gustation.
10.If you completely dry the surface of your tongue
and then place salt or sugar crystals on it, you
cannot taste them. Why not?

38. © 2013 Pearson Education, Inc.
The Accessory Structures of the Eye (9-5)
1. Eyelids and associated exocrine glands
2. The superficial epithelium of the eye
3. Structures associated with the production,
secretion, and removal of tears
4. The extrinsic eye muscles

39. © 2013 Pearson Education, Inc.
The Eyelids (9-5)
• Also called palpebrae
• Upper and lower eyelids join at the medial canthus and
lateral canthus
• At the medial canthus, glands that secrete gritty "sleep"
are found in the lacrimal caruncle
• Have sebaceous glands that can become infected,
known as a sty

40. © 2013 Pearson Education, Inc.
Conjunctiva (9-5)
• Inner surface of the eyelids
• And the outer, white surface of the eye, up to the
edge of the cornea
• Irritation or damage to the conjunctiva is called
conjunctivitis, or pinkeye

41. © 2013 Pearson Education, Inc.
The Lacrimal Apparatus (9-5)
• Produces essential tears, distributes them across
the eye, and removes them
• The lacrimal gland secretes the tears and is
superior and lateral to the eyeball
• Tears drain through two pores at the medial
canthus called the lacrimal canals and into the
nasolacrimal duct
PLAYPLAY ANIMATION The Eye: Accessory Structures

42. © 2013 Pearson Education, Inc.
Figure 9-8a The Accessory Structures of the Eye.
Lateral
canthus
Sclera
Eyelashes
Pupil
Palpebra
(eyelid)
Iris
Medial
canthus
Lacrimal
caruncle
Gross and superficial anatomy of
the accessory structures

43. © 2013 Pearson Education, Inc.
Figure 9-8b The Accessory Structures of the Eye.
Lacrimal
pores
Superior
lacrimal canal
Lacrimal sac
Inferior
lacrimal canal
Nasolacrimal
duct
Opening of
duct into
nasal cavity
The organization of the
lacrimal apparatus
Lacrimal gland Lacrimal gland ducts

44. © 2013 Pearson Education, Inc.
The Extrinsic Eye Muscles (9-5)
• Control the position of the eye and include:
• Inferior rectus
• Medial rectus
• Superior rectus
• Lateral rectus
• Inferior oblique
• Superior oblique

45. © 2013 Pearson Education, Inc.
Frontal
bone
Superior
oblique
TrochleaSuperior
rectus
Optic
nerve
Lateral
rectus
Inferior
rectus Maxilla Inferior oblique
Lateral surface, right eye
Superior
rectus
Lateral
rectus
Inferior
oblique
Anterior view, right eye
Inferior
rectus
Medial
rectus
Superior
oblique
Trochlea
Figure 9-9 The Extrinsic Eye Muscles.

46. © 2013 Pearson Education, Inc.
Table 9-1 The Extrinsic Eye Muscles

47. © 2013 Pearson Education, Inc.
The Eye (9-5)
• Found in the orbit with the:
• Lacrimal glands
• Extrinsic eye muscles
• Cranial nerves
• Blood vessels
• Orbital fat cushions the eye

48. © 2013 Pearson Education, Inc.
The Eyeball (9-5)
• The eyeball is hollow and divided into two
cavities
1. Posterior cavity
• Filled with jellylike vitreous body
2. Anterior cavity has two subdivisions
• The anterior and posterior chambers
• Filled with aqueous humor

49. © 2013 Pearson Education, Inc.
The Fibrous Layer of the Eyeball (9-5)
• The sclera
• The white of the eye
• Supportive dense connective tissue
• The cornea
• Transparent
• Allows light to enter the eye

50. © 2013 Pearson Education, Inc.
The Vascular Layer of the Eyeball (9-5)
• Contains blood and lymphatic vessels, and the
intrinsic eye muscles
• Functions
1. Providing a route for vessels supplying the tissue
2. Adjusting the amount of light entering the eye
3. Providing a route for secreting and reabsorbing
aqueous humor
4. Controlling the shape of the lens

51. © 2013 Pearson Education, Inc.
The Vascular Layer of the Eyeball (9-5)
• Structures
• The iris, with pupillary muscles that change the size of
the pupil, the "window" into the eye
• The ciliary body, which contains the ciliary muscle and
ciliary processes, and the suspensory ligaments,
which adjust the shape of the lens for focusing
• The choroid, a highly vascular tissue
PLAYPLAY ANIMATION The Eye: Cilliary Muscles

52. © 2013 Pearson Education, Inc.
Figure 9-10a The Sectional Anatomy of the Eye.
Optic nerve
Eyelash
Conjunctiva
Cornea
Pupil
Iris
Lens
Fovea
Sagittal section of left eye

53. © 2013 Pearson Education, Inc.
Figure 9-10b The Sectional Anatomy of the Eye.
Posterior
cavity
Anterior
cavity
Horizontal section of right eye
Sclera
Cornea
Fibrous
layer
Choroid
Iris
Ciliary body
Vascular layer
Neural part
Inner layer
(retina)
Pigmented part

54. © 2013 Pearson Education, Inc.
Figure 9-10c The Sectional Anatomy of the Eye.
Cornea
Iris
Suspensory ligament of
lens
Conjunctiva
Lower eyelid
Sclera
Choroid
Retina
Posterior
cavity
Lateral rectus
muscle
Fovea
Orbital fat
Lens
Edge of
pupil
Anterior cavity
Posterior
chamber
Anterior
chamber
Nose
Lacrimal pore
Ciliary
muscle
Ciliary body
Medial rectus
muscle
Optic disc
Optic nerve
Central artery
and vein
Lacrimal sac
Horizontal dissection of right eye
Visual axis

55. © 2013 Pearson Education, Inc.
Figure 9-11 The Pupillary Muscles.
The pupillary constrictor
muscles form a series of
concentric circles around the pupil.
When these sphincter muscles
contract, the diameter of the pupil
decreases.
The pupillary dilator
muscles extend radially away
from the edge of the pupil.
Contraction of these muscles
enlarges the pupil.
.
Pupillary constrictor
(sphincter)
Decreased light intensity
Increased sympathetic stimulation
Increased light intensity
Increased parasympathetic stimulation
Pupil
Pupillary dilator
(radial)

56. © 2013 Pearson Education, Inc.
The Inner Layer (9-5)
• Also called the retina
• The inner layer includes:
• A pigmented part, which absorbs light
• A neural part that contains the photoreceptors
• Supportive cells and neurons
• Blood vessels

57. © 2013 Pearson Education, Inc.
Photoreceptors (9-5)
• Rods
• Used in dim light
• Found on the periphery of retinal surface
• Cones
• Used in bright light and detect color
• Found in the macula, the center of which is the fovea,
or fovea centralis

58. © 2013 Pearson Education, Inc.
The Inner Layer (9-5)
• Rods and cones synapse with bipolar cells,
which synapse with ganglion cells
• Ganglion cells
• These axons leave the back of the eye through the
optic disc, the origin of the optic nerve
• The blind spot is where there are no photoreceptors on
the retina
PLAYPLAY ANIMATION The Eye: The Retina

59. © 2013 Pearson Education, Inc.
Figure 9-12a Retinal Organization.
Nuclei of
ganglion cells
Nuclei of rods
and cones
Nuclei of
bipolar cells
Retina LM x 350
Choroid
Pigmented
part of retina
Rods and
cones
Bipolar
cells
Ganglion
cells
LIGHT
Amacrine
cell
Horizontal cell Cone Rod
The cellular organization of the retina. The photoreceptors are closest to
the choroid, rather than near the posterior cavity (vitreous chamber).

60. © 2013 Pearson Education, Inc.
Figure 9-12b Retinal Organization.
Pigmented
part of retina
Neural part
of retina
Central
retinal vein
Central
retinal artery
Sclera
Choroid
Optic
nerve
The optic disc in diagrammatic
sagittal section.
Optic
disc

61. © 2013 Pearson Education, Inc.
Figure 9-12c Retinal Organization.
Fovea
Optic disc
(blind spot)
Macula
Central retinal artery and vein
emerging from center of optic disc
A photograph of the retina as seen
through the pupil.

62. © 2013 Pearson Education, Inc.
Figure 9-13 A Demonstration of the Presence of a Blind Spot.

63. © 2013 Pearson Education, Inc.
The Chambers of the Eye (9-5)
• Anterior cavity
• Anterior chamber extends from the cornea to the iris
• Posterior chamber between the iris and the lens
• Filled with aqueous humor produced by the ciliary
processes
• Maintains pressure in eye
• Drains out through the scleral venous sinus

64. © 2013 Pearson Education, Inc.
The Chambers of the Eye (9-5)
• Problems with fluid and pressure is a condition
called glaucoma
• Posterior cavity
• Filled with the vitreous body
• Holds the retina in place

65. © 2013 Pearson Education, Inc.
Figure 9-14 The Circulation of Aqueous Humor.
Posterior cavity
(vitreous chamber)
Scleral venous
sinus
Body of iris
Conjunctiva
Ciliary
body
Sclera
Choroid
Retina
Cornea
Pupil
Ciliary
process
Suspensory
ligaments
Pigmented
epithelium
Anterior cavity
Anterior chamber
Posterior chamber
Lens

66. © 2013 Pearson Education, Inc.
The Lens (9-5)
• Posterior to cornea
• Held in place by suspensory ligaments
• Cells
• Are wrapped in concentric circle
• Elastic fibers make lens spherical
• Changes shape to accommodate for focus

67. © 2013 Pearson Education, Inc.
Light Refraction and Accommodation (9-5)
• Light is bent or refracted as it enters the cornea
and lens
• Light rays converge on retina at focal point
• Focal distance is between lens and focal point
• For far-away objects, the ciliary muscles relax, flattening
the lens
• For close objects, the lens accommodates by rounding
when the ciliary muscles contract
PLAYPLAY ANIMATION The Eye: Light Path

68. © 2013 Pearson Education, Inc.
Figure 9-15a-c Focal Point, Focal Distance, and Visual Accommodation.
Focal distance
Light
from
distant
source
(object)
Close
source
Focal
point
Focal distance Focal distance
Lens
The closer the light source,
the longer the focal distance
The rounder the lens,
the shorter the focal distance

69. © 2013 Pearson Education, Inc.
Figure 9-15d-e Focal Point, Focal Distance, and Visual Accommodation.
Focal point
on fovea
Lens rounded Lens flattened
Ciliary muscle
contracted
Ciliary muscle
relaxed
For Close Vision: Ciliary Muscle Contracted,
Lens Rounded
For Distant Vision: Ciliary Muscle Relaxed,
Lens Flattened

70. © 2013 Pearson Education, Inc.
Light rays projected from a vertical object
show why the image arrives upside down.
(Note that the image is also reversed.)
Light rays projected from a horizontal
object show why the image arrives with a
left and right reversal. The image also
arrives upside down. (As noted in the text,
these representations are not drawn to
scale.)
Figure 9-16 Image Formation.

71. © 2013 Pearson Education, Inc.
Figure 9-17 Accommodation Problems (1 of 3)
The eye has a fixed
focal distance and
focuses by varying the
shape of the lens.
A camera focuses an
image by moving the
lens toward or away
from the film. This
method cannot work
in our eyes, because
the distance from the
lens to the macula
cannot change. We
focus images on the
retina by changing the
shape of the lens to
keep the focal
distance constant, a
process called
accommodation.
A camera lens has a fixed
size and shape and
focuses by varying the
distance to the film or
semiconductor device.

72. © 2013 Pearson Education, Inc.
Figure 9-17 Accommodation Problems (2 of 3)
Emmetropia
(normal vision)
In the healthy eye, when
the ciliary muscle is
relaxed and the lens is
flattened, a distant image
will be focused on the
retina’s surface. This
condition is called
emmetropia (emmetro-,
proper + opia, vision).

73. © 2013 Pearson Education, Inc.
Figure 9-17 Accommodation Problems (3 of 3)
Myopia (nearsightedness)
If the eyeball is too deep or the rest-
ing curvature of the lens is too great,
the image of a distant object is
projected in front of the retina. The
person will see distant objects as
blurry and out of focus. Vision at
close range will be normal because
the lens is able to round as needed to
focus the image on the retina.
Hyperopia (farsightedness)
If the eyeball is too shallow or the lens
is too flat, hyperopia results. The
ciliary muscle must contract to focus
even a distant object on the retina.
And at close range the lens cannot
provide enough refraction to focus an
image on the retina. Older people
become farsighted as their lenses lose
elasticity, a form of hyperopia called
presbyopia (presbys, old man).
Myopia
corrected
with a
diverging,
con-
cave
lens
Hyperopia
corrected with
a converging,
convex
lens
Diverging
lens
Converging
lens

74. © 2013 Pearson Education, Inc.
Checkpoint (9-5)
11. Which layer of the eye would be the first to be
affected by inadequate tear production?
12. When the lens is more rounded, are you looking
at an object that is close to you or far from you?
13. As Malia enters a dimly lit room, most of the
available light becomes focused on the fovea of
her eye. Will she be able to see very clearly?

75. © 2013 Pearson Education, Inc.
Photoreceptors Respond to Photons (9-6)
• Photons are units of visible light
• Red, orange, yellow, green, blue, indigo, violet
• Color determined by wavelength
• Photons of red have longest wavelength, least energy
• Photons of violet have shortest wavelength, most
energy

76. © 2013 Pearson Education, Inc.
Photoreceptors in the Eye (9-6)
• Rods
• Respond to presence or absence of photons regardless of
wavelength
• Very sensitive, therefore effective in dim light
• Cones
• Three different types
• Blue cones, green cones, red cones
• Contain pigments sensitive to blue, green, or red
wavelengths of light
• Less sensitive, therefore function only in bright light

77. © 2013 Pearson Education, Inc.
Color Blindness (9-6)
• Occurs when one or more types of cone is not functioning
or is missing
• Most common is red-green color blindness where red
cones are missing
• More common in males (10 percent) than females
(0.67 percent)
• Total color blindness is extremely rare (1 person in
300,000)

78. © 2013 Pearson Education, Inc.
Figure 9-18 A Standard Test for Color Vision.

79. © 2013 Pearson Education, Inc.
The Structure of Photoreceptors (9-6)
• Outer segment contains hundreds to thousands of
flattened discs
• Contain visual pigments that absorb photons and initiate
photoreception
• Made of compound rhodopsin that contains opsin and
retinal (derived from vitamin A)
• Retinal is the same in rods and cones, opsin is different
• Inner segment contains organelles, synapses with bipolar
cells

80. © 2013 Pearson Education, Inc.
Figure 9-19a The Structure of Rods and Cones.
Discs
Connecting
stalks
Golgi
apparatus
Cone Rods
LIGHT
Bipolar cell
Mitochondria
Pigment
Epithelium
Absorbs photons
not absorbed by
visual pigments.
Melanin
granules
Outer Segment
Visual pigments
are contained in
membrane
discs.
Inner Segment
Site of major
organelles and cell
functions other
than photoreception.
It also releases
neurotransmitters.
Each photoreceptor
synapses with a
bipolar cell.
Nuclei

81. © 2013 Pearson Education, Inc.
Figure 9-19b The Structure of Rods and Cones.
Retinal
Rhodopsin
molecule
Opsin
Structure of rhodopsin
molecule

82. © 2013 Pearson Education, Inc.
Photoreception (9-6)
• Photon strikes rhodopsin
• Retinal and opsin break apart, referred to as
bleaching
• Alters rate of neurotransmitter release into
synapse with bipolar cell
• For rod or cone to be able to respond to light
again, the opsin and retinal must recombine

83. © 2013 Pearson Education, Inc.
Retinal and
opsin are
reassembled
to form
rhodopsin
Photon
Retinal changes shape
Regeneration
enzyme
Bleaching
(separation)
Retinal restored
Opsin
Opsin
inactivated
Opsin
Figure 9-20 Bleaching and Regeneration of Visual Pigments.

84. © 2013 Pearson Education, Inc.
The Visual Pathways (9-6)
• Photoreceptor  bipolar cell  ganglion cell
• Axons from optic nerves (N II)  optic chiasm
• Medial fibers cross, lateral fibers do not cross
• Optic tracts  thalamic nuclei
• Superior colliculi of midbrain controls eye reflexes
• Thalamic axons  visual cortex of cerebrum

85. © 2013 Pearson Education, Inc.
Combined Visual Field
Left side Right side
Binocular vision
Right
eye
only
The Visual
Pathway
Photoreceptors
in retina
Optic nerve
(N II)
Optic chiasm
Optic tract
Thalamic
nucleus
Projection fibers
Visual cortex
of cerebral
hemispheres
Retina
Optic disc
Hypothalamus,
pineal gland,
and reticular
formation
Superior
colliculus
Left cerebral
hemisphere
Right cerebral
hemisphere
Left
eye
only
The Visual Pathways (9-6)

86. © 2013 Pearson Education, Inc.
Checkpoint (9-6)
14. Are individuals born without cone cells able to see?
Explain.
15. How would a diet deficient in vitamin A affect vision?

87. © 2013 Pearson Education, Inc.
Anatomy of the Ear (9-7)
• External ear
• Visible portion, collects sound waves
• Middle ear
• Chamber with structures that amplify sound waves
• Internal ear
• Contains sensory organs for hearing and equilibrium
PLAYPLAY ANIMATION The Ear: Ear Anatomy

88. © 2013 Pearson Education, Inc.
External Ear Middle Ear Internal Ear
Elastic cartilages Auditory ossicles
Auricle
Oval
window
Semicircular canals
Temporal bone
Facial nerve
(N VII)
Vestibulocochl-
ear nerve (N VIII)
Bony labyrinth
of internal ear
Cochlea
Auditory tube
To
nasopharynx
VestibuleRound
window
Tympanic
membrane
External acoustic
meatus
Figure 9-22 The Anatomy of the Ear.

89. © 2013 Pearson Education, Inc.
The External Ear (9-7)
• Auricle or pinna is fleshy "cup" directing sound
into ear
• External acoustic meatus or auditory canal
• Contains ceruminous glands, secreting earwax
• Tympanic membrane or eardrum
• Thin sheet that vibrates when sound waves strike it

90. © 2013 Pearson Education, Inc.
The Middle Ear (9-7)
• Also called the tympanic cavity
• Air-filled chamber
• Auditory tube
• Also called pharyngotympanic or Eustachian tube
• Leads to the pharynx, making a path for
microorganisms to trigger otitis media, an infection
• Allows for pressure equalization on either side of
eardrum

91. © 2013 Pearson Education, Inc.
The Auditory Ossicles (9-7)
• Three small bones in middle ear that connect
tympanic membrane to internal ear
1. Malleus attaches to eardrum
2. Incus attaches malleus to innermost bone
3. Stapes has a base that nearly fills the oval window into
the internal ear

92. © 2013 Pearson Education, Inc.
Temporal bone
Connections to
mastoid air cells
Stabilizing
ligament
Branch of facial
nerve VII (cut)
External
acoustic meatus
Tympanic
membrane
Auditory Ossicles
Malleus Incus Stapes
Oval
window Muscles of
the Middle Ear
Tensor tympani
muscle
Stapedius muscle
Round window
Auditory tube
Figure 9-23 The Middle Ear.

93. © 2013 Pearson Education, Inc.
The Internal Ear (9-7)
• Sensory structures protected by bony labyrinth
• Contains fluid perilymph between bony and
membranous labyrinths
• Inside bony labyrinth is membranous labyrinth
• Tubes that follow contours of bony labyrinth
• Filled with fluid endolymph

94. © 2013 Pearson Education, Inc.
Three Parts of the Bony Labyrinth (9-7)
1. Vestibule
• Contains membranous saccule and utricle with
receptors for gravity and linear acceleration
2. Semicircular canals
• Contain membranous semicircular ducts with
receptors for rotational acceleration
3. Vestibular complex is the combination of the
first two, providing sense of balance

95. © 2013 Pearson Education, Inc.
Three Parts of the Bony Labyrinth (9-7)
3. Cochlea
• Contains the membranous cochlear duct
• Sensory receptors for hearing
• Oval window is covered with thin membrane
separating perilymph in cochlea from air in middle ear
• Round window is opening in the bone of the cochlea

96. © 2013 Pearson Education, Inc.
Hair Cells (9-7)
• Sensory receptors in internal ear
• Surrounded by supporting cells
• Synapse with dendrites of sensory neurons
• Free surface covered with stereocilia
• Movement of stereocilia alters neurotransmitter release
• Bending stereocilia in one direction triggers
depolarization; in the other direction, hyperpolarization

97. © 2013 Pearson Education, Inc.
Figure 9-24a The Internal Ear and a Hair Cell.
Perilymph
Bony labyrinth
Endolymph
Membranous
labyrinth
A section through one of the semicir-
cular canals, showing the relationship
between the bony and membranous
labyrinths, and the locations of peri-
lymph and endolymph.
KEY
Membranous labyrinth
Bony labyrinth

98. © 2013 Pearson Education, Inc.
Figure 9-24b The Internal Ear and a Hair Cell.
Semicircular
Ducts
Anterior
Posterior
Vestibule
Crista ampullaris
Maculae
Endolymphatic sac
Utricle
Saccule
Cochlear duct
Semicircular canal
Scala tympani Spiral organ
Scala vestibuli
Lateral
The bony and membranous labyrinths. Areas of the
membranous labyrinth containing sensory receptors
(cristae, maculae, and spiral organ) are shown in purple.
KEY
Membranous labyrinth
Bony labyrinth
Cochlea

99. © 2013 Pearson Education, Inc.
Figure 9-24c The Internal Ear and a Hair Cell.
Displacement in this
direction inhibits hair cell
Stereocilia
Hair cell
Sensory
neuron
Supporting
cell
A representative hair cell (receptor) from the vestibular
complex. Bending the stereocilia in one direction depolarizes
the cell and stimulates the sensory neuron. Displacement in the
opposite direction inhibits the sensory neuron.
Displacement in this
direction stimulates
hair cell

100. © 2013 Pearson Education, Inc.
• Dynamic equilibrium
• Maintaining balance while in motion
• Monitored by semicircular ducts
• Static equilibrium
• Maintaining balance and posture while motionless
• Monitored by saccule and utricle
Equilibrium (9-7)

101. © 2013 Pearson Education, Inc.
The Semicircular Ducts (9-7)
• Three ducts
1. Anterior
2. Posterior
3. Lateral
• Organized in three planes
1. Transverse
2. Frontal
3. Sagittal

102. © 2013 Pearson Education, Inc.
The Semicircular Ducts (9-7)
• Each contains the ampulla, which contains the
sensory receptors
• The crista ampullaris contains hair cells that are
embedded in gelatinous structure called the
cupula
• When head rotates, endolymph pushes against
the cristae and activates hair cells

103. © 2013 Pearson Education, Inc.
The Vestibule (9-7)
• Saccule receptors
• Respond to gravity and linear acceleration
• Utricle receptors
• Respond to horizontal acceleration
• Hair cells clustered in maculae
• Project into gelatinous membrane with otoliths
• Gravity pulls on otoliths, pulling on hair cells

104. © 2013 Pearson Education, Inc.
The locations of
equilibrium receptors,
a crista ampullaris
and a macula.
Figure 9-25a The Vestibular Complex.

105. © 2013 Pearson Education, Inc.
Figure 9-25b The Vestibular Complex.
Ampulla
filled with
endolymph
Hair cells
Crista
ampullaris
Cupula
Supporting cells
Sensory nerve
A cross section through the ampulla of a
semicircular duct showing the crista ampullaris.

106. © 2013 Pearson Education, Inc.
Figure 9-25c The Vestibular Complex.
Direction of
rotation
Direction of
endolymph movement
Direction of
rotation
Semicircular duct
Cupula
At rest
Endolymph movement along the axis of the
semicircular duct moves the cupula and
stimulates the hair cells.

107. © 2013 Pearson Education, Inc.
Figure 9-25d The Vestibular Complex.
Gelatinous layer
forming otolithic
membrane
Otoliths
Hair cells
Nerve
fibers
The structure of an individual macula.

108. © 2013 Pearson Education, Inc.
Figure 9-25e The Vestibular Complex.
Head in normal, upright
position
Gravity
Head tilted posteriorly
Gravity
Receptor
output
increases
Otolith
moves
“downhill,”
distorting hair
cell processes
A diagrammatic view of macular function
when the head is held horizontally
and then tilted back .

109. © 2013 Pearson Education, Inc.
Pathways for Equilibrium Sensations (9-7)
• Hair cells of vestibule and semicircular ducts
• Synapse with neurons of vestibular branch of N VIII
• These synapse with neurons in the vestibular nuclei of
the pons and medulla oblongata
• Information is relayed to:
• Cerebellum
• Cerebral cortex
• Motor nuclei in brain stem and spinal cord
PLAYPLAY ANIMATION The Ear: Balance

110. © 2013 Pearson Education, Inc.
Hearing (9-7)
• Vibrations of sound waves determine stimulus
• Tympanic membrane vibrates the ossicles
• Pressure pulses travel through perilymph of cochlea
• Pitch (frequency) determined by which part of cochlear
duct is stimulated
• Volume (intensity) determined by how many hair cells
are activated at that site

111. © 2013 Pearson Education, Inc.
The Cochlear Duct (9-7)
• Sectional view shows three chambers
1. Scala vestibuli (the vestibular duct)
2. Scala media (the cochlear duct)
3. Scala tympani (the tympanic duct)
• Scala vestibuli and scala tympani are filled with
perilymph and are a continuous chamber

112. © 2013 Pearson Education, Inc.
The Spiral Organ of Corti (9-7)
• Located in cochlear duct on basilar membrane
• Hair cell stereocilia project into tectorial
membrane, attached to wall of cochlear duct
• Waves strike basilar membrane, moving it up and
down
• Hair cells are pushed against tectorial membrane,
bending stereocilia

113. © 2013 Pearson Education, Inc.
Figure 9-26a The Cochlea and Spiral Organ.
Bony cochlear wall
Scala vestibuli
Vestibular membrane
Tectorial membrane
Basilar membrane
Scala tympani
Spiral organ
Spiral
ganglion
Cochlear branch
of N VIII
Cochlear duct
A three-dimensional section of the
cochlea, showing the compartments,
tectorial membrane, and spiral organ

114. © 2013 Pearson Education, Inc.
Figure 9-26b The Cochlea and Spiral Organ.
Tectorial membrane
Outer
hair cell
Basilar membrane Inner hair cell Nerve fibers
Cochlear duct (scala media)
Vestibular membrane
Tectorial membrane
Scala
tympani
Basilar
membrane
Hair cells
of spiral
organ
Spiral ganglion
cells of
cochlear nerve
Spiral organ
Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ
LM x 125

115. © 2013 Pearson Education, Inc.
Six Steps of Hearing (9-7)
1. Sound waves strike tympanic membrane
2. Tympanic membrane vibrates auditory ossicles
3. Vibration of stapes applies pressure to perilymph
4. Pressure distorts basilar membrane
5. Movement of basilar membrane distorts hair cells
against tectorial membrane, altering neurotransmitter
release
6. Impulses travel to CNS through N VIII

116. © 2013 Pearson Education, Inc.
Figure 9-27 Sound and Hearing.
External
acoustic
meatus
Malleus Incus Stapes Oval window
Cochlear branch
of cranial nerve
VIII
Scala vestibuli
(contains perilymph)
Vestibular membrane
Cochlear duct
(contains endolymph)
Basilar membrane
Scala tympani
(contains perilymph)
Tympanic
membrane
Round
window
Sound
waves
arrive at
tympanic
membrane.
Movement
of the
tympanic
membrane
causes
displacem-
ent of the
auditory
ossicles.
Movement
of the stapes
at the oval
window
establishes
pressure
waves
in the
perilymph
of the scala
vestibuli.
The
pressure
waves distort
the basilar
membrane
on their way
to the
round
window
of the scala
tympani.
Vibration of
the basilar
membrane
causes
vibration
of hair cells
against the
tectorial
membrane.
Information
about the
region and
the intensity
of stimulation
is relayed to
the CNS over
the cochlear
branch of
cranial nerve
VIII.
Movement
of sound
waves

117. © 2013 Pearson Education, Inc.
Auditory Pathways (9-7)
• Cochlear branch of vestibulocochlear nerve
(N VIII) axons arise from spiral ganglion
• To cochlear nuclei of medulla oblongata
• To inferior colliculi of midbrain
• To nuclei in thalamus
• To auditory cortex of temporal lobes

118. © 2013 Pearson Education, Inc.
Figure 9-28 Pathways for Auditory Sensations.
Stimulation of hair cells
at a specific location
along the basilar
membrane activates
sensory neurons.
Projection fibers then
deliver the information
to specific locations
within the auditory
cortex of the temporal
lobe.
High-
frequency
sounds
Thalamus
Cochlea
Low-frequency
sounds
High-frequency
sounds
Vestibular
branch
Sensory neurons carry
the sound information
in the cochlear branch
of the vestibulocochlear
nerve (VIII) to the
cochlear nucleus on
that side.
Low-frequency
sounds
Ascending acoustic
information synapes at
a nucleus of the
thalamus.
The inferior colliculi direct a variety
of unconscious motor responses to
sounds.
Information ascends from each
cochlear nucleus to the inferior
colliculi of the midbrain.
Motor output to spinal cord
Vestibulocochlear
nerve (VIII)
KEY
Primary pathway
Secondary pathway
Motor output

119. © 2013 Pearson Education, Inc.
Checkpoint (9-7)
16. If the round window were not able to bulge out
with increased pressure in the perilymph, how
would sound perception be affected?
17. How would the loss of stereocilia from the hair
cells of the spiral organ affect hearing?

120. © 2013 Pearson Education, Inc.
Aging and the Special Senses (9-8)
• Olfaction and gustation decrease with decrease in
number and sensitivity of receptors
• Hearing decreases with age due to loss of
elasticity of tympanic membrane

121. © 2013 Pearson Education, Inc.
Checkpoint (9-8)
18. How can a given food be both too spicy for a
child and too bland for an elderly individual?
19. Explain why we have an increasingly difficult
time seeing close-up objects as we age.