© 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
© 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.
© 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.
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Sensory Receptors (9-1)
• Can be special cell processes
• Or separate cells
• Monitor conditions both inside and outside the
body
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Free Nerve Endings (9-1)
• The simplest receptors
• Are modified dendritic endings
• Examples:
• Touch receptors
• Pain receptors
• Heat receptors
• Taste receptors
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Separate Receptor Cells (9-1)
• Complex structures
• Associated with supportive cells
• Examples:
• Visual receptors in the eyes
• Auditory receptors in the ears
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The Receptive Field (9-1)
• The area monitored by a single receptor
• The smaller the field, the more precise the sensory
information
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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
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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
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General Senses (9-1)
• Temperature
• Pain
• Touch
• Pressure
• Vibration
• Proprioception (body position)
• Occur throughout the body
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Special Senses (9-1)
• Olfaction (smell)
• Gustation (taste)
• Vision
• Equilibrium (balance)
• Hearing
• Concentrated in the sense organs and located in
the head
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Figure 9-1 Receptors and Receptive Fields.
Receptivefield 1
Receptivefield 2
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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.
© 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
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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
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Liver and
gallbladder
Heart
Stomach
Smallintestine
Appendix
Colon
Ureters
Figure 9-2 Referred Pain.
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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
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Three Classes of Mechanoreceptors
1. Tactile receptors
• Touch
2. Baroreceptors
• Pressure
3. Proprioceptors
• Position
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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
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Free nerve endings
Root hairplexus
Tactile discs innervatingMerkel cells
Tactile disc
Merkel cells
Tactile corpuscle
Dermis
Dendrites
Lamellated corpuscle
Dermis
Dendrite
Ruffini corpuscle
Sensorynerve fiber
DendritesFreenerve
ending
Tactilecorpuscle
Tactile disc(innervatingMerkel cell)
Hair
Root hairplexus
Lamellatedcorpuscle
Ruffinicorpuscle
Sensorynerves
Figure 9-3 Tactile Receptors in the Skin.
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Baroreceptors (9-2)
• Monitor changes in pressure in the viscera
• Adapt readily
• Found in the major blood vessels, lungs, digestive,
and urinary tracts
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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
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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
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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
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Figure 9-5 Locations and Functions of Chemoreceptors.
Chemoreceptors in and
near Respiratory Centers
of Medulla Oblongata
Trigger reflexiveadjustments in
depth and rate ofrespiration
Chemoreceptors
of Carotid Bodies
Chemoreceptors
of Aortic Bodies
Trigger reflexiveadjustments inrespiratory andcardiovascular
activity
Cranialnerve IX
Cranialnerve X
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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?
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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
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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
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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
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Figure 9-6a The Olfactory Organs.
Olfactory Pathway to the Cerebrum
Olfactoryepithe-lium
OlfactorynerveFibers(N I)
Olfactorytract
Centralnervoussystem
Cribriformplate
Superiornasal
concha
The olfactory organ on the right
side of the nasal septum.
Olfactorybulb
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Figure 9-6b The Olfactory Organs.
Basal cell:divides to
replaceworn-outolfactoryreceptor
cells
Olfactorygland
Toolfactory
bulb
Cribriformplate
Areolartissue
Olfactoryepithelium
Substance being smelled
Olfactorynerve fibers
Developingolfactoryreceptor cell
Olfactoryreceptor cell
Supporting cell
Mucous layer
Olfactory cilia:surfaces containreceptor proteins
An olfactory receptor is a modified neuronwith multiple cilia extending from its freesurface.
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Checkpoint (9-3)
7. Define olfaction.
8. How does repeated sniffing help to identify faint
odors?
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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
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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
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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
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Water receptors(pharynx) Umami
Tastebuds
TastebudsSour
BitterSaltySweet
Circumvallate papilla
Taste buds LM x 280
Supportingcell
Gustatorycell
Taste hairs(microvilli)
Tastepore
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.
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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?
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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
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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
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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
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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
PLAY ANIMATION The Eye: Accessory Structures
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Figure 9-8a The Accessory Structures of the Eye.
Lateralcanthus
Sclera
Eyelashes
Pupil
Palpebra(eyelid)
Iris
Medialcanthus
Lacrimal caruncle
Gross and superficial anatomy of the accessory structures
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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
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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
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Frontalbone
Superioroblique
TrochleaSuperiorrectus
Opticnerve
Lateralrectus
Inferiorrectus Maxilla Inferior oblique
Lateral surface, right eye
Superiorrectus
Lateralrectus
Inferioroblique
Anterior view, right eye
Inferiorrectus
Medialrectus
Superioroblique
Trochlea
Figure 9-9 The Extrinsic Eye Muscles.
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Table 9-1 The Extrinsic Eye Muscles
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The Eye (9-5)
• Found in the orbit with the:
• Lacrimal glands
• Extrinsic eye muscles
• Cranial nerves
• Blood vessels
• Orbital fat cushions the eye
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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
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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
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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
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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
PLAY ANIMATION The Eye: Cilliary Muscles
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Figure 9-10a The Sectional Anatomy of the Eye.
Optic nerve
EyelashConjunctiva
Cornea
Pupil
Iris
Lens
Fovea
Sagittal section of left eye
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Figure 9-10b The Sectional Anatomy of the Eye.
Posteriorcavity
Anteriorcavity
Horizontal section of right eye
Sclera
Cornea
Fibrous
layer
Choroid
Iris
Ciliary body
Vascular layer
Neural part
Inner layer
(retina)
Pigmented part
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Figure 9-10c The Sectional Anatomy of the Eye.
Cornea
Iris
Suspensory ligament oflens
Conjunctiva
Lower eyelid
Sclera
Choroid
Retina
Posteriorcavity
Lateral rectusmuscle
Fovea
Orbital fat
Lens
Edge ofpupil
Anterior cavity
Posteriorchamber
Anteriorchamber
Nose
Lacrimal pore
Ciliary
muscle
Ciliary body
Medial rectus
muscle
Optic disc
Optic nerve
Central arteryand vein
Lacrimal sac
Horizontal dissection of right eye
Visual axis
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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)
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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
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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
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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
PLAY ANIMATION The Eye: The Retina
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Figure 9-12a Retinal Organization.
Nuclei ofganglion cells
Nuclei of rodsand cones
Nuclei ofbipolar cells
Retina LM x 350
Choroid
Pigmentedpart of retina
Rods andcones
Bipolarcells
Ganglioncells
LIGHT
Amacrinecell
Horizontal cell Cone Rod
The cellular organization of the retina. The photoreceptors are closest tothe choroid, rather than near the posterior cavity (vitreous chamber).
© 2013 Pearson Education, Inc.
Figure 9-12b Retinal Organization.
Pigmentedpart of retina
Neural partof retina
Centralretinal vein
Centralretinal artery
Sclera
Choroid
Optic nerve
The optic disc in diagrammatic sagittal section.
Opticdisc
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Figure 9-12c Retinal Organization.
Fovea
Optic disc(blind spot)
MaculaCentral retinal artery and vein
emerging from center of optic disc
A photograph of the retina as seen through the pupil.
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Figure 9-13 A Demonstration of the Presence of a Blind Spot.
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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
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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
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Figure 9-14 The Circulation of Aqueous Humor.
Posterior cavity(vitreous chamber)
Scleral venoussinus
Body of iris
ConjunctivaCiliarybody
Sclera
Choroid
Retina
Cornea
Pupil
Ciliaryprocess
Suspensoryligaments
Pigmentedepithelium
Anterior cavity
Anterior chamber
Posterior chamber
Lens
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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
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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
PLAY ANIMATION The Eye: Light Path
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Figure 9-15a-c Focal Point, Focal Distance, and Visual Accommodation.
Focal distance
Light
from
distant
source
(object)
Closesource
Focalpoint
Focal distance Focal distance
Lens
The closer the light source,
the longer the focal distance
The rounder the lens,
the shorter the focal distance
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Figure 9-15d-e Focal Point, Focal Distance, and Visual Accommodation.
Focal point
on fovea
Lens rounded Lens flattened
Ciliary musclecontracted
Ciliary musclerelaxed
For Close Vision: Ciliary Muscle Contracted,
Lens Rounded
For Distant Vision: Ciliary Muscle Relaxed,
Lens Flattened
© 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.
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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 calledaccommodation.
A camera lens has a fixed size and shape and
focuses by varying the distance to the film or semiconductor device.
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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. Thiscondition is calledemmetropia (emmetro-, proper + opia, vision).
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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. Theciliary 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 calledpresbyopia (presbys, old man).
Myopia
corrected
with a
diverging,
con-
cave
lens
Hyperopia
corrected with
a converging,
convex
lens
Diverginglens
Converginglens
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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?
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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
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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
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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)
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Figure 9-18 A Standard Test for Color Vision.
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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
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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
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Figure 9-19b The Structure of Rods and Cones.
Retinal
Rhodopsinmolecule
Opsin
Structure of rhodopsinmolecule
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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
© 2013 Pearson Education, Inc.
Retinal andopsin are
reassembledto form
rhodopsin
Photon
Retinal changes shape
Regenerationenzyme
Bleaching(separation)
Retinal restored
Opsin
Opsininactivated
Opsin
Figure 9-20 Bleaching and Regeneration of Visual Pigments.
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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
© 2013 Pearson Education, Inc.
Combined Visual Field
Left side Right side
Binocular vision
Righteyeonly
The Visual
Pathway
Photoreceptorsin retina
Optic nerve(N II)
Optic chiasm
Optic tract
Thalamicnucleus
Projection fibers
Visual cortexof cerebral
hemispheres
Retina
Optic disc
Hypothalamus,pineal gland,and reticular
formation
Superiorcolliculus
Left cerebralhemisphere
Right cerebralhemisphere
Lefteyeonly
The Visual Pathways (9-6)
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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?
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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
PLAY ANIMATION The Ear: Ear Anatomy
© 2013 Pearson Education, Inc.
External Ear Middle Ear Internal Ear
Elastic cartilages Auditory ossicles
Auricle
Ovalwindow
Semicircular canals
Temporal bone
Facial nerve
(N VII)
Vestibulocochl-
ear nerve (N VIII)
Bony labyrinth
of internal ear
Cochlea
Auditory tubeTo
nasopharynx
VestibuleRound
window
Tympanic
membrane
External acoustic
meatus
Figure 9-22 The Anatomy of the Ear.
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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
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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
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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
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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
Ovalwindow Muscles of
the Middle Ear
Tensor tympanimuscle
Stapedius muscle
Round window
Auditory tube
Figure 9-23 The Middle Ear.
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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
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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
• Vestibular complex is the combination of the
first two, providing sense of balance
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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
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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
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Figure 9-24a The Internal Ear and a Hair Cell.
PerilymphBony labyrinth
EndolymphMembranous
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 labyrinthBony labyrinth
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Figure 9-24b The Internal Ear and a Hair Cell.
Semicircular
Ducts
Anterior
Posterior
VestibuleCrista ampullarisMaculaeEndolymphatic sac
UtricleSaccule
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 labyrinthBony labyrinth
Cochlea
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Figure 9-24c The Internal Ear and a Hair Cell.
Displacement in thisdirection inhibits hair cell
Stereocilia
Hair cell
Sensoryneuron
Supportingcell
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 thisdirection stimulates
hair cell
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• 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)
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The Semicircular Ducts (9-7)
• Three ducts
1. Anterior
2. Posterior
3. Lateral
• Organized in three planes
1. Transverse
2. Frontal
3. Sagittal
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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
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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
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The locations ofequilibrium receptors, a crista ampullarisand a macula.
Figure 9-25a The Vestibular Complex.
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Figure 9-25b The Vestibular Complex.
Ampullafilled with
endolymph
Hair cells
Cristaampullaris
Cupula
Supporting cells
Sensory nerve
A cross section through the ampulla of asemicircular duct showing the crista ampullaris.
© 2013 Pearson Education, Inc.
Figure 9-25c The Vestibular Complex.
Direction ofrotation
Direction ofendolymph movement
Direction ofrotation
Semicircular ductCupula
At rest
Endolymph movement along the axis of thesemicircular duct moves the cupula andstimulates the hair cells.
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Figure 9-25d The Vestibular Complex.
Gelatinous layerforming otolithic
membrane
Otoliths
Hair cells
Nervefibers
The structure of an individual macula.
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Figure 9-25e The Vestibular Complex.
Head in normal, upright
positionGravity
Head tilted posteriorly
Gravity
Receptoroutput
increases
Otolithmoves
“downhill,”distorting haircell processes
A diagrammatic view of macular functionwhen the head is held horizontally and then tilted back .
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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
PLAY ANIMATION The Ear: Balance
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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
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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
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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
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Figure 9-26a The Cochlea and Spiral Organ.
Bony cochlear wall
Scala vestibuli
Vestibular membrane
Tectorial membrane
Basilar membrane
Scala tympani
Spiral organ
Spiralganglion
Cochlear branchof N VIII
Cochlear duct
A three-dimensional section of thecochlea, showing the compartments,tectorial membrane, and spiral organ
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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
Scalatympani
Basilarmembrane
Hair cellsof spiralorgan
Spiral ganglioncells of
cochlear nerve
Spiral organ
Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ
LM x 125
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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
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Figure 9-27 Sound and Hearing.
Externalacousticmeatus
Malleus Incus Stapes Oval windowCochlear branchof cranial nerveVIII
Scala vestibuli(contains perilymph)
Vestibular membrane
Cochlear duct(contains endolymph)
Basilar membrane
Scala tympani(contains perilymph)
Tympanicmembrane
Roundwindow
Sound
wavesarrive attympanicmembrane.
Movement
of thetympanicmembranecausesdisplacem-ent of theauditoryossicles.
Movement
of the stapesat the ovalwindowestablishespressurewavesin theperilymphof the scalavestibuli.
The
pressurewaves distortthe basilarmembraneon their wayto theroundwindowof the scalatympani.
Vibration of
the basilarmembranecausesvibrationof hair cellsagainst thetectorialmembrane.
Information about the region and the intensity of stimulation is relayed to the CNS over
the cochlear
branch of
cranial nerve
VIII.
Movementof sound
waves
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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
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Figure 9-28 Pathways for Auditory Sensations.
Stimulation of hair cells at a specific location along the basilarmembrane 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-frequencysounds
Vestibularbranch
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 thethalamus.
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 pathwaySecondary pathwayMotor output
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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?
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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
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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.