PowerLecture: Chapter 14

1
PowerLectureChapter 14

• Sensory Systems

2
Learning Objectives

• Describe the characteristics of a receptor and
  list the various types of receptors.
• Contrast mechanisms by which the chemical and the
  somatic senses work.
• Understand how the senses of balance and hearing
  function.
• Describe how the sense of vision has evolved
  through time.

3
Learning Objectives (contd)

• Draw a medial section of the human eyeball
  through the optic nerve, identify each structure,
  and tell the function of each.
• Identify some common disorders of the eye.

4
Impacts/Issues

• Private Eyes

5
Private Eyes

• Iris scanning is one of the newest
• security techniques.
• First, each persons unique
• arrangement of smooth muscle fibers in
• the iris of the eye must be recorded in
• an electronic database.
• Each time the person passes through
• a check point, a small camera looks at the iris
  and compares it with the database.
• Usually, we use our eyes to see, but in this new
  technology, our eyes are seen.

6
How Would You Vote?

• To conduct an instant in-class survey using a
  classroom response system, access JoinIn Clicker
  Content from the PowerLecture main menu.
• In which situations should individuals be
  required to submit to iris scanning and
  registration?
• a. For any reason it's not any different than
  other forms of identification.
• b. In place of or to enhance government
  identification, such as a driver's license or
  passport.
• c. For employment at any company that chooses to
  require it.
• d. It should never be required, it should only be
  used as a voluntary convenience, and then,
  strictly regulated.

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Section 1

• Sensory Receptors and Pathways

8
Sensory Receptors and Pathways

• In a sensory system, a stimulus activates a
  receptor, which transduces (converts) it to an
  action potential that travels to the brain where
  it triggers sensation or perception.
• A stimulus is any form of energy that activates
  receptor endings of a sensory neuron.
• Sensations are conscious responses to the
  stimuli.
• Perception is an understanding of what sensations
  mean.

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In-text Fig., p. 250
stimulus energy received
stimulus energy converted to action potential
brain response (sensation or perception)
10
Fig. 14.1, p. 251
Stretched muscle stimulates a stretch receptor
(the ending of a sensory neuron) that is adjacent
to it.
c
d
Message travels from stimulated sensory neuron to
motor neuron and interneuron in spinal cord.
sensory neuron
interneuron in spinal cord
motor neuron in spinal cord
e
Message is sent back to the muscle, also to
other interneurons in the brain.
axon endings of motor neuron terminating on the
same muscle
muscle spindle
b
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Sensory Receptors and Pathways

• Six major categories of sensory receptors.
• Mechanoreceptors detect changes in pressure,
  position, or acceleration.
• Thermoreceptors detect heat or cold.
• Nociceptors (pain receptors) detect tissue
  damage.
• Chemoreceptors detect ions or molecules.
• Osmoreceptors detect changes in solute
  concentration in surrounding fluid.
• Photoreceptors detect the energy of visible
  light.

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Animation Mechanoreceptors
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13
(No Transcript)
14
Sensory Receptors and Pathways

• All action potentials are the same the brain
  determines the nature of a given stimulus based
  on which nerves are signaling, the frequency of
  the action potentials generated, and the number
  of axons responding.
• Specific sensory areas interpret action
  potentials in specific ways.
• Strong signals make receptors fire action
  potentials more often and longer.

15
Sensory Receptors and Pathways

• Stronger stimuli recruit more sensory receptors.
• Sensory adaptation is the diminishing response to
  an ongoing stimulus.

Figure 14.1
16
Section 2

• Somatic Sensations

17
Somatic Sensations

• Somatic sensations occur when receptor signals
  from body surfaces reach the somatosensory cortex
  in the cerebrum.

Figure 14.3
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Animation Somatosensory Cortex
CLICKTO PLAY
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Somatic Sensations

• Receptors near the body surface sense touch,
  pressure, and more.
• Sensations of touch, pressure, cold, warmth, and
  pain are discerned near the body surface by
  receptors whose numbers vary by body region.
• Free nerve endings are the simplest receptors.
• These are thinly myelinated or unmyelinated
  dendrites of sensory neurons.
• One type coils around hair follicles to detect
  movement another detects chemicals.

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Somatic Sensations

• Encapsulated receptors are surrounded by a
  capsule of epithelial or connective tissue.
• Merkels discs adapt slowly and
• are important for steady touch.
• Meissners corpuscles respond
• to light touching.
• Ruffini endings are sensitive to
• steady touch and pressure.
• The Pacinian corpuscles are
• sensitive to deep pressure and
• vibrations.

Figure 14.4
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Animation Sensory Receptors
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Fig. 14.4, p. 253
free nerve endings (pain)
Meissners corpuscle (light touch)
hair
Meissners corpuscle
epidermis
Merkels discs (steady touch)
Ruffini endings (pressure, touch)
dermis
Merkels discs
subcutaneous layer
Pacinian corpuscle (deep pressure, vibrations)
hair follicle receptor (hair displacement)
Ruffini endings
Pacinian corpuscle
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Somatic Sensations

• Mechanoreceptors in skeletal muscle, joints,
  tendons, ligaments, and skin are responsible for
  awareness of the bodys position and of its limb
  movements.
• Pain is the perception of bodily injury.
• Pain is the perception of injury to some region
  of the body.

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Somatic Sensations

• Nociceptors are subpopulations of free nerve
  endings distributed throughout the skin (somatic
  pain) and internal tissues (visceral pain).
• When cells are damaged, they release chemicals
  (bradykinins, histamine, and prostaglandins) to
  activate neighboring pain receptors.
• Pain receptors signal interneurons, which release
  substance P.
• Substance P allows for natural opiates called
  endorphins and enkephalins to be released to
  reduce pain perception.

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Somatic Sensations

• Referred pain is a matter of perception.
• Much visceral pain is referred pain that is,
• it is felt at some distance from the real
  stimulation point.
• Phantom pain is the sensation that amputees feel
  when they sense the missing part as if it were
  still there.

26
Fig. 14.5, p. 253
lungs,diaphragm
heart
stomach
liver, gallbladder
pancreas
small intestine
ovaries
colon
appendix
urinary bladder
kidney
ureter
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Animation Referred Pain
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Section 3

• Taste and Smell
• Chemical Senses

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Taste and Smell Chemical Senses

• Taste and smell are chemical senses they begin
  at chemoreceptors, the signals traveling to the
  brain where they are perceived, transmitted to
  the limbic system, and remembered.

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Taste and Smell Chemical Senses

• Gustation is the sense of taste.
• Sensory organs called taste buds hold the taste
  receptors.
• Receptors are located on the tongue, roof of the
  mouth, and throat.
• The five general taste categories are sweet,
  sour, salty, bitter, and umami.
• The flavors of most foods are a combination of
  the five basic tastes plus sensory input from
  olfactory receptors in the nose.

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Animation Taste Receptors
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Fig. 14.6, p. 254
a
taste bud
tonsil
hairlike ending of taste receptor
bitter
sour
salty
sweet
c
sensory nerve
d
b
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Taste and Smell Chemical Senses

• Olfaction is the sense of smell.
• Olfactory receptors in the olfactory epithelium
  of the nose detect water-soluble or volatile
  substancesodors.
• The interpretation of smell is done by the
  olfactory bulbs located in the brain.
• Olfaction is one of the most ancient senses,
  useful in survival as the receptors respond to
  molecules from food, mates, and predators.
• Humans also have a vomeronasal organ whose
  receptors can detect pheromones, which are
  signaling molecules with roles in sexual
  attraction.

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Animation Olfactory Pathway
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35
Fig. 14.7, p. 255
olfactory nerve tract
olfactory bulb
olfactory receptor cell body
36
Video Tongue Tied
CLICKTO PLAY

• From ABC News, Human Biology in the Headlines,
  2006 DVD.

37
Section 4

• A Tasty Morsel of Sensory Science

38
A Tasty Morsel of Sensory Science

• Receptors in taste buds associate the five main
  taste categories with particular tastant
  molecules that the brain interprets depending on
  the action potentials that come its way.
• Each taste bud has receptors that can respond to
  tastants of at least two, if not all five, of the
  taste classes.
• Not all taste receptors, however, are equally
  sensitive bitter receptors tend to be the most
  sensitive.

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A Tasty Morsel of Sensory Science

• Various tastants commingle together with odors
  into what we perceive as flavors.

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Section 5

• Hearing Detecting Sound Waves

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Hearing Detecting Sound Waves

• Sounds are waves of compressed air the amplitude
  (loudness) and frequency (pitch) of sounds are
  detected by vibration-sensitive mechanoreceptors
  deep in the ear.

one cycle
Low note
Soft
Amplitude
High note
Loud
Same loudness, different pitch
Same frequency, different amplitude
Frequency per unit time
Figure 14.8
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Animation Wavelike Properties of Sound
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Hearing Detecting Sound Waves

• The ear gathers and sends sound signals to the
  brain.
• The outer ear collects sound waves and turns them
  into vibrations, which are amplified in the
  middle ear vibrations are distinguished in the
• inner ear.
• Inner ear structures include semicircular canals
  for balance and the cochlea where hearing takes
  place.

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Hearing Detecting Sound Waves

• Sensory hair cells are the key to hearing.
• Vibrations are passed from the tympanic membrane
  to the middle ear bones (malleus, incus, stapes)
  and on to the oval window, stretched across the
  entrance to the cochlea.
• Sound is amplified because the oval window is
  smaller than the tympanic membrane.
• The cochlea has two compartments in its outer
  chamber (the scala vestibuli and scala tympani),
  which curl around an inner cochlear duct all are
  fluid filled.

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Fig. 14.9a, p. 256
46
Fig. 14.9a, p. 256
INNER EAR vestibular apparatus, cochlea
MIDDLE EAR eardrum, ear bones
OUTER EAR pinna, auditory canal
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Fig. 14.9b, p. 256
OVAL WINDOW (behind stirrup)
MIDDLE EAR BONES
stirrup
auditory nerve
anvil
hammer
COCHLEA
round window
auditory canal
EARDRUM
48
Fig. 14.9c, p. 257
oval window (behind stirrup)
waves of air pressure
waves of fluid pressure
scala vestibuli
eardrum
scala tympani
cochlear duct
round window
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Hearing Detecting Sound Waves

• Vibrations of the oval window send pressure waves
  through the fluid to the basilar membrane on the
  floor of the cochlear duct resting on the
  membrane is the organ of Corti, which includes
  sensory hair cells.
• The tips of the hair cells rest against the
  jellylike tectorial membrane vibrations cause
  the hair cells to bend.
• Bending causes the release of neurotransmitters,
  triggering action potentials that travel to the
  brain.

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scala vestibuli
cochlear duct
organ of Corti
scala tympani
sensory neurons (to the auditory nerve)
Fig. 14.9d, p. 257
51
Hearing Detecting Sound Waves

• Loudness is determined by the total number of
  cells that become stimulated tone or pitch
  depends on the frequency of vibration.
• The round window at the far end of the cochlea
  serves as a release valve for the pressure waves
  in the middle ear.
• The eustachian tube extending from the middle ear
  to the throat permits equalization of pressures.

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Animation Ear Structure and Function
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Video Sound Detection
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Section 6

• Balance Sensing the Bodys Natural Position

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Balance Sensing the Bodys Natural Position

• The sense of balance depends on messages from
  receptors in the eyes, skin, and joints, as well
  as organs of equilibrium in the inner ear.
• The vestibular apparatus is a closed system of
  fluid-filled sacs and semicircular canals inside
  the ear the canals are arranged to represent the
  three planes of space.

Figure 14.10
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Animation Vestibular Apparatus and Equilibrium
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Balance Sensing the Bodys Natural Position

• Rotational receptors are located at the base of
  each semicircular canal sensory hair cells
  project into a jellylike cupula.
• Movement of the head causes the hairs to bend
  within the jelly, generating action potentials.
• Rotation of the head determines dynamic
  equilibrium.

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Animation Dynamic Equilibrium
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59
Balance Sensing the Bodys Natural Position

• Static equilibrium, the heads position in space,
  is monitored by two sacs in the vestibular
  apparatus, the utricle and saccule.
• The sacs contain the otolith organs (hair cells)
  and otoliths (ear stones), which detect changes
  in orientation as well as acceleration and
  deceleration.
• Action potentials from different parts of the
  vestibular apparatus travel to reflex centers in
  the brainstem.
• As signals are integrated, the brain orders
  compensatory movements necessary to maintain
  postural balance.

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Fig. 14.10, p. 258
vestibular apparatus, a system of fluid-filled
sacs and canals inside the ear
A vestibular apparatus (part of each inner ear)
consists of a utricle, a saccule, and the three
canals labeled here.
superior canal
posterior canal
utricle
horizontal canal
saccule
nerve
fluid pressure
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stereocilium
otolith
cupula
hair cell
sensory neuron
Fig. 14.11, p. 258
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Balance Sensing the Bodys Natural Position

• Extreme motion or continuous overstimulation of
  the hair cells of the vestibular apparatus can
  result in motion sickness.

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Section 7

• Disorders of the Ear

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Disorders of the Ear

• The hearing apparatus of the ears is sturdy, but
  it can be damaged by various illnesses and
  injuries.
• Otitis media, painful inflammation of the middle
  ear, often occurs in children following spread of
  a respiratory infection pus and/or fluid buildup
  as a result can cause the eardrum to rupture.
• Tinnitus, or ringing or buzzing in the ears, can
  be triggered by infection, aspirin consumption,
  or other, unknown causes.

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Disorders of the Ear

• Deafness is the partial or complete loss of
  hearing deafness may be congenital or due to
  aging, disease, or environmental causation.
• The loudness of sounds is measured in decibels.
• Quiet conversation occurs at about 50 decibels.
• Damage begins when exposed to sounds
• between 75-85 decibels over extended periods.
• Rock concerts easily reach 130 decibels.

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Outer Hair Cells
scars
Fig. 14.13, p. 259
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Section 8

• Vision An Overview

68
Vision An Overview

• Vision is an awareness of the position, shape,
  brightness, distance, and movement of visual
  stimuli as detected by the sensory organs, the
  eyes.
• The eye is built for photoreception.
• The eye has three layers, sometimes called
  tunics.
• The outer layer consists of the sclera and
  transparent cornea.
• The middle layer consists of a choroid, ciliary
  body, and iris.
• The inner layer is the retina.

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Vision An Overview

• The sclera (white of the eye) protects the eye
  the dark-pigmented choroid underlies the sclera
  and prevents light from scattering. Most of the
  blood vessels lie in the choroid.
• Behind the cornea is the pigmented iris the hole
  at the center of the iris is the pupil, the
  entrance for light which can be adjusted
  depending on the level of light present.
• The lens is found behind the iris the lens is
  attached to the ciliary body, a muscle
  functioning in the focusing of light.
• The lens focuses light onto a layer of
  photoreceptor cells in the retina.

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Vision An Overview

• A clear fluid (aqueous humor) bathes both sides
  of the lens vitreous humor fills the chamber
  behind the lens.
• The retina is a thin layer of neural tissue at
  the back of the eyeball axons from some of the
  neurons converge to form the optic nerve, which
  sends signals to the visual cortex in the
  thalamus.

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Animation Eye Structure
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Parts of the Eye
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Vision An Overview

• The curved surface of the cornea bends incoming
  light so that light rays converge at the back of
  the eyeball images appear upside down and
  backwards on the retina but are corrected in the
  brain.
• Eye muscle movements fine-tune the focus.
• Because of the bending of the light rays by the
  cornea, accommodation must be made by the lens so
  that the image is in focus on the retina.
• Accommodation is performed by the ciliary muscles
  attached to the lens.

74
Vision An Overview

• Eye muscle movements fine-tune the focus.
• Because of the bending of the light rays by the
  cornea, accommodation must be made by the lens so
  that the image is in focus on the retina.
• Accommodation is performed by the ciliary muscles
  attached to the lens.

75
Fig. 14.15a, p. 261
76
Fig. 14.16, p. 261
muscle contracted
close object
slack fibers
Accommodation for close objects (lens bulges)
muscle relaxed
distant object
taut fibers
Accommodation for distant objects (lens flattens)
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Animation Visual Accomodation
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Video To See Again
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• From ABC News, Biology in the Headlines, 2005 DVD.

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Section 9

• From Visual Signals
• to Sight

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From Visual Signals to Sight

• Rods and cones are the photoreceptors.
• The retinas basement layer is pigmented and is
  covered by photoreceptors called rod cells and
  cone cells.
• Rod cells are sensitive to dim light and detect
  changes in light intensity cone cells respond to
  high-intensity light and contribute to sharp
  daytime vision.

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Fig. 14.17a, p. 262
82
Fig. 14.17b, p. 262
rod cell
stacked, pigmented membranes
cone cell
83
From Visual Signals to Sight

• Visual pigments in rods and cones intercept light
  energy.

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From Visual Signals to Sight

• Each rod contains more than a billion molecules
  of rhodopsin this pigment can detect and respond
  to even a few photons of light, allowing us to
  see in dim light.
• Rhodopsin consists of a protein (opsin) and a
  signal molecule (cis-retinal) that is derived
  from vitamin A.
• Photons of blue-green light stimulate rhodopsin
  to change shape shape changes alter the
  distribution of ions across the rod cell membrane
  and slow down the release of an inhibitory
  neurotransmitter.
• Without the inhibitor, neurons send visual
  signals to the brain.

85
From Visual Signals to Sight

• Cone cells have different visual pigments (red,
  green, or blue) absorption of photons also
  prevents release of neurotransmitters, thus
  allowing signaling to the brain.
• Visual acuity is
• greatest in the fovea,
• a depression located
• at the center of the
• retina that is densely
• packed with
• photoreceptors.

Figure 14.18
86
From Visual Signals to Sight

• The retina processes signals from rods and cones.
• Signals flow from rods and cones to bipolar
  interneurons, and then to ganglion cells, the
  axons of which form the optic nerves.
• Before leaving the retina, signals are dampened
  or enhanced by horizontal cells and amacrine
  cells.

87
Fig. 14.19, p. 263
horizontal cells
amacrine cells
rods
cones
incoming rays of light
ganglion cells (axons get bundled into one of two
optic nerves)
bipolar cells
88
Animation Organization of Cells in the Retina
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89
From Visual Signals to Sight

• Receptive fields in the retina.
• The retinas surface is organized into receptive
  fields, areas that influence the activity of
  individual sensory neurons.
• Some fields respond to differences in light,
  others to motion, color, or rapid changes in
  light intensity.
• Signals move on to the visual cortex.
• The visual field represents the part of the
  outside world a person actually sees.
• The right side of each retina gathers light from
  the left half of the visual field and the left
  side gathers light from the right half of the
  field.

90
From Visual Signals to Sight

• The optic nerve from each eye sends signals from
  the left visual field to the right cerebral
  hemisphere, and signals from the right visual
  field to the left hemisphere.
• Axons of the optic nerves end in the lateral
  geniculate nucleus, from which they proceed to
  the brains visual cortex, which has several
  visual fields sensitive to direction, movement,
  color, and so on here is where final
  interpretation of the signals is made to produce
  an organized sense of sight.

91
Fig. 14.20, p. 263
lateral geniculate nucleus
to optic nerve
optic nerve
visual cortex
retina
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Animation Pathway to the Visual Cortex
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93
Section 10

• Disorders of the Eye

94
Disorders of the Eye

• Normal eye function can be disrupted by disease,
  injury, inherited abnormalities, and aging.
• Missing cone cells cause color blindness.
• Total color blindness results when an individual
  has only one of the three kinds of cones.

95
Disorders of the Eye

• Red-green color blindness is the inability to
  distinguish red and green colors in dim light
  (and sometimes bright light) due to a lack of red
  and green cone cells.
• Malformed eye parts cause common focusing
  problems.
• In astigmatism, one or both corneas have uneven
  curvature and cannot bend light to the same focal
  point.

Figure 14.23
96
Disorders of the Eye

• Nearsightedness (myopia) results when the image
  is focused in front of the retina.
• Farsightedness (hyperopia) is due to an image
  focused behind the retina.

Figure 14.21
97
Fig. 14.21 (top), p. 264
(focal point)
(focal point)
distant object
close object
98
Fig. 14.21 (bottom), p. 264
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Animation Focusing Problems
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100
Disorders of the Eye

• The eyes are also vulnerable to infections and
  cancer.
• Conjunctivitis, inflammation of the membrane
  lining the inside of the eyelids and covering the
  sclera, is among the
• most common reasons
• for doctor visits in the
• U.S.

Figure 14.22
101
Disorders of the Eye

• Trachoma, caused by the bacterium responsible for
  the sexually transmitted disease chlamydia,
  damages both the eyeball and the conjunctiva,
  possibly leading to blindness.
• Herpes infection of the cornea results from
  infection with various herpes simplex viruses and
  can also lead to blindness.
• Malignant melanoma is eye cancer that develops in
  the choroid retinoblastoma is cancer of the
  retina that occurs in infants.

102
Disorders of the Eye

• Aging increases the risk of cataracts and some
  other eye disorders.
• Cataracts, the gradual clouding of the lens
  associated with aging and diabetes, can
  completely block light from entering the eye.
• Macular degeneration is an age-related
  degeneration of the retina.
• Glaucoma results from excess of fluid in the
  eyeball, causing pressure on the retina.

103
Disorders of the Eye

• Medical technologies can remedy some vision
  problems and treat eye injuries.
• Corneal transplant surgery can replace defective
  corneas with artificial plastic corneas or donor
  corneas cataracts may be corrected in a similar
  fashion by replacing the lens.
• Lasik (laser-assisted in situ keratomilieusis)
  or lasek (laser-assisted subepithelial
  keratectomy) surgeries can be used to correct
  severe nearsightedness.

104
Disorders of the Eye

• Conductive keratoplasty (CK) uses radio waves to
  reshape the cornea.
• Retinal detachment can result from a physical
  blow to the head laser coagulation can be used
  to reattach the retina to the underlying
  choroid.