Transcript You Light Up My Life

PowerLecture:
Chapter 14
Sensory Systems
Learning Objectives
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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.
Learning Objectives (cont’d)
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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.
Impacts/Issues
Private Eyes
Private Eyes
Iris scanning is one of the newest
security techniques.
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First, each person’s 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.
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menu.
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In which situations should individuals be required to
submit to iris scanning and registration?
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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.
Section 1
Sensory Receptors and
Pathways
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.
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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.
stimulus
energy
received
stimulus energy
converted to
action potential
brain response
(sensation or
perception)
In-text Fig., p. 250
c Stretched muscle stimulates
d Message travels from stimulated
a stretch receptor (the ending of a
sensory neuron to motor neuron
sensory neuron) that is adjacent to it.
and interneuron in spinal cord.
sensory neuron
interneuron in spinal cord
motor neuron in spinal cord
axon endings of motor
neuron terminating on
the same muscle
b
e Message is sent back to
the muscle, also to other
interneurons in the brain.
muscle spindle
Fig. 14.1, p. 251
Sensory Receptors and Pathways
Six major categories of sensory receptors.
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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.
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.
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Specific sensory areas interpret action
potentials in specific ways.
Strong signals make receptors fire action
potentials more often and longer.
Sensory Receptors and Pathways
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Stronger stimuli recruit more sensory receptors.
Sensory adaptation is the diminishing
response to an ongoing stimulus.
Figure 14.1
Section 2
Somatic Sensations
Somatic Sensations
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Somatic
sensations
occur when
receptor signals
from body
surfaces reach
the
somatosensory
cortex in the
cerebrum.
Figure 14.3
Somatic Sensations
Receptors near the body surface sense
touch, pressure, and more.
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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.
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These are thinly myelinated or unmyelinated
dendrites of sensory neurons.
One type coils around hair follicles to detect
movement; another detects chemicals.
Somatic Sensations
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Encapsulated receptors are surrounded by a
capsule of epithelial or connective tissue.
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Merkel’s discs adapt slowly and
are important for steady touch.
Meissner’s 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
free nerve
endings
hair
(pain)
Meissner’s
corpuscle
(light touch)
dermis
Merkel’s discs
(steady touch)
Meissner’s
corpuscle
Ruffini endings
(pressure, touch)
Merkel’s discs
hair follicle
receptor
(hair displacement)
Pacinian
corpuscle
(deep pressure,
vibrations)
Ruffini
endings
Pacinian corpuscle
Fig. 14.4, p. 253
Somatic Sensations
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Mechanoreceptors in skeletal muscle, joints,
tendons, ligaments, and skin are responsible
for awareness of the body’s position and of its
limb movements.
Pain is the perception of bodily injury.
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Pain is the perception of injury to some region
of the body.
Somatic Sensations
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Nociceptors are subpopulations of free nerve
endings distributed throughout the skin
(somatic pain) and internal tissues (visceral
pain).
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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.
Somatic Sensations
Referred pain is a matter of perception.
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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.
lungs,diaphragm
heart
stomach
liver, gallbladder
pancreas
small intestine
ovaries
colon
appendix
urinary bladder
kidney
ureter
© 2007 Thomson Higher Education
Fig. 14.5, p. 253
Section 3
Taste and Smell:
Chemical Senses
Taste and Smell: Chemical Senses
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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.
Taste and Smell: Chemical Senses
Gustation is the sense of taste.
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Sensory organs called taste buds hold the
taste receptors.
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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.
a
tonsil
taste
bud
hairlike
ending
of taste
receptor
bitter
sour
salty
sweet
b
c
d sensory nerve
Fig. 14.6, p. 254
Taste and Smell: Chemical Senses
Olfaction is the sense of smell.
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Olfactory receptors in the olfactory epithelium
of the nose detect water-soluble or volatile
substances—odors.
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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.
olfactory nerve tract
olfactory bulb
olfactory
receptor
cell body
© 2007 Thomson Higher Education
Fig. 14.7, p. 255
Section 4
A Tasty Morsel of
Sensory Science
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.
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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.
A Tasty Morsel of Sensory Science
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Various tastants commingle together with
odors into what we perceive as flavors.
Section 5
Hearing: Detecting
Sound Waves
Hearing: Detecting Sound Waves
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Sounds are waves of compressed air; the
amplitude (loudness) and frequency
(pitch) of sounds are detected by vibrationsensitive mechanoreceptors deep in the
ear.
Amplitude
one cycle
Frequency per
unit time
Soft
Low
note
Loud
High
note
Same frequency,
different amplitude
Same loudness,
different pitch
Figure 14.8
Hearing: Detecting Sound Waves
The ear gathers and sends “sound signals”
to the brain.
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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.
Hearing: Detecting Sound Waves
Sensory hair cells are the key to hearing.
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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.
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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.
Fig. 14.9a, p. 256
INNER EAR
vestibular apparatus,
cochlea
OUTER EAR
pinna, auditory
canal
MIDDLE EAR
eardrum,
ear bones
Fig. 14.9a, p. 256
MIDDLE EAR BONES
OVAL WINDOW (behind stirrup)
stirrup
auditory nerve
anvil
hammer
COCHLEA
auditory EARDRUM
canal
round
window
Fig. 14.9b, p. 256
oval window
(behind stirrup)
waves of air
pressure
scala vestibuli
eardrum
© 2007 Thomson Higher Education
waves of
fluid
pressure
scala tympani
round window
cochlear duct
Fig. 14.9c, p. 257
Hearing: Detecting Sound Waves
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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.
scala vestibuli
cochlear duct
organ of Corti
sensory
neurons (to the
auditory nerve)
scala tympani
Fig. 14.9d, p. 257
Hearing: Detecting Sound Waves
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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.
Section 6
Balance: Sensing the
Body’s Natural Position
Balance: Sensing the
Body’s 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.
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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
Balance: Sensing the
Body’s Natural Position
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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.
Balance: Sensing the
Body’s Natural Position
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Static equilibrium, the head’s position in
space, is monitored by two sacs in the
vestibular apparatus, the utricle and saccule.
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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.
vestibular apparatus, a
system of fluid-filled sacs
and canals inside the ear
posterior
canal
horizontal
canal
superior canal
utricle
saccule
A vestibular
apparatus (part
of each inner
ear) consists of
a utricle, a
saccule, and
the three canals
labeled here.
nerve
fluid pressure
Fig. 14.10, p. 258
stereocilium
otolith
cupula
hair
cell
sensory
neuron
Fig. 14.11, p. 258
Balance: Sensing the
Body’s Natural Position
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Extreme motion or continuous
overstimulation of the hair cells of the
vestibular apparatus can result in motion
sickness.
Section 7
Disorders of the Ear
Disorders of the Ear
The hearing apparatus of the ears is sturdy,
but it can be damaged by various illnesses
and injuries.
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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.
Disorders of the Ear
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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.
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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.
Outer Hair
Cells
scars
Fig. 14.13, p. 259
Section 8
Vision: An Overview
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.
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The eye has three layers, sometimes called
“tunics.”
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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.
Vision: An Overview
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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.
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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.
Vision: An Overview
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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.
Parts of
the Eye
Vision: An Overview
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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.
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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.
Vision: An Overview
Eye muscle movements fine-tune the focus.
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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.
Fig. 14.15a, 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)
Fig. 14.16, p. 261
Video: To See Again
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From ABC News, Biology in the Headlines, 2005 DVD.
Section 9
From Visual Signals
to “Sight”
From Visual Signals to “Sight”
Rods and cones are the photoreceptors.
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The retina’s 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.
Fig. 14.17a, p. 262
rod cell
stacked, pigmented membranes
cone cell
Fig. 14.17b, p. 262
From Visual Signals to “Sight”
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Visual pigments in rods and cones intercept
light energy.
From Visual Signals to “Sight”
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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.
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•
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.
From Visual Signals to “Sight”
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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
From Visual Signals to “Sight”
The retina processes signals from rods and
cones.
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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.
horizontal cells
amacrine cells
rods
cones
incoming
rays of
light
ganglion cells (axons
get bundled into one
of two optic nerves)
bipolar cells
Fig. 14.19, p. 263
From Visual Signals to “Sight”
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Receptive fields in the retina.
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The retina’s 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.
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•
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.
From Visual Signals to “Sight”
•
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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 brain’s 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.
to
optic nerve
optic nerve
lateral
geniculate nucleus
visual cortex
retina
Fig. 14.20, p. 263
Section 10
Disorders of the Eye
Disorders of the Eye
Normal eye function can be disrupted by
disease, injury, inherited abnormalities, and
aging.
Missing cone cells cause color blindness.
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Total color blindness results when an individual
has only one of the three kinds of cones.
Disorders of the Eye
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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.
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In astigmatism, one or both corneas have
uneven curvature and cannot bend light to the
same focal point.
Figure 14.23
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
(focal
point)
(focal
point)
distant
object
close
object
Fig. 14.21 (top), p. 264
Fig. 14.21 (bottom), p. 264
Disorders of the Eye
The eyes are also vulnerable to infections
and cancer.
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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
Disorders of the Eye
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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.
Disorders of the Eye
Aging increases the risk of cataracts and
some other eye disorders.
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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.
Disorders of the Eye
Medical technologies can remedy some
vision problems and treat eye injuries.
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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.
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.