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Chapter 45: Sensory Systems
CHAPTER 45
Sensory Systems
Chapter 45: Sensory Systems
Chapter 45: Sensory Systems
Sensory Cells, Sensory Organs, and
Transduction
Chemoreceptors: Responding to Specific
Molecules
Mechanoreceptors: Detecting Stimuli that
Distort Membranes
Chapter 45: Sensory Systems
Chapter 45: Sensory Systems
Photoreceptors and Visual Systems:
Responding to Light
Sensory Worlds Beyond Our Experience
Chapter 45: Sensory Systems
Sensory Cells, Sensory
Organs, and Transduction
• Sensory cells transduce information about
an animal’s external and internal
environment into action potentials.
Review Figures 45.1, 45.2
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Chapter 45: Sensory Systems
figure 45-01a.jpg
Figure
45.1 – Part
1
Figure 45.1 – Part 1
Chapter 45: Sensory Systems
figure 45-01b.jpg
Figure 45.1
– Part 2
Figure 45.1 – Part 2
Chapter 45: Sensory Systems
figure 45-02.jpg
Figure
45.2
Figure 45.2
Chapter 45: Sensory Systems
Sensory Cells, Sensory
Organs, and Transduction
• The interpretation of action potentials as
particular sensations depends on which
neurons in the CNS receive them.
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Chapter 45: Sensory Systems
Sensory Cells, Sensory
Organs, and Transduction
• Membrane receptor proteins of sensory cells
cause ion channels to open or close,
generating receptor potentials.
• Receptor potentials can spread to regions of
the sensory cell plasma membrane that
generate action potentials, or influence
release of neurotransmitter from the
sensory cell.
Review Figure 45.3
Chapter 45: Sensory Systems
figure 45-03.jpg
Figure
45.3
Figure 45.3
Chapter 45: Sensory Systems
Sensory Cells, Sensory
Organs, and Transduction
• Adaptation enables the nervous system to
ignore irrelevant stimuli while remaining
responsive to relevant or to new stimuli.
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Chapter 45: Sensory Systems
Chemoreceptors: Responding
to Specific Molecules
• Smell, taste, and the sensing of pheromones
are examples of chemosensation.
• Chemoreceptor cells have receptor proteins
that can bind to specific molecules that
come into contact with the sensory cell
membrane.
Review Figures 45.5, 45.6
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Chapter 45: Sensory Systems
figure 45-05.jpg
Figure
45.5
Figure 45.5
Chapter 45: Sensory Systems
Chemoreceptors: Responding
to Specific Molecules
• Binding of an odorant molecule to a
receptor protein causes production of a
second messenger in the chemoreceptor
cell.
• The second messenger alters ion channels
and creates a receptor potential.
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Chapter 45: Sensory Systems
Chemoreceptors: Responding
to Specific Molecules
• Chemoreceptors in the mouth cavities of
vertebrates are responsible for the sense of
taste.
Review Figure 45.6
16
Chapter 45: Sensory Systems
figure 45-06.jpg
Figure
45.6
Figure 45.6
Chapter 45: Sensory Systems
Mechanoreceptors: Detecting
Stimuli that Distort Membranes
• The skin has a diversity of
mechanoreceptors that respond to touch
and pressure.
• The density of mechanoreceptors in any
skin area determines the sensitivity of that
area.
Review Figure 45.7
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Chapter 45: Sensory Systems
figure 45-07.jpg
Figure 45.7
Figure 45.7
Chapter 45: Sensory Systems
Mechanoreceptors: Detecting
Stimuli that Distort Membranes
• Stretch receptors in muscles, tendons, and
ligaments inform the CNS of the positions of
and the loads on parts of the body.
Review Figure 45.8
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Chapter 45: Sensory Systems
figure 45-08.jpg
Figure
45.8
Figure 45.8
Chapter 45: Sensory Systems
Mechanoreceptors: Detecting
Stimuli that Distort Membranes
• Hair cells are mechanoreceptors that are not
neurons.
• Bending of their stereocilia alters their
membrane proteins and therefore their
receptor potentials.
• Hair cells are found in organs of equilibrium
and orientation.
Review Figures 45.9, 45.10, 45.11
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Chapter 45: Sensory Systems
figure 45-09.jpg
Figure
45.9
Figure 45.9
Chapter 45: Sensory Systems
figure 45-10.jpg
Figure
45.10
Figure 45.10
Chapter 45: Sensory Systems
figure 45-11a.jpg
Figure
45.11 – Part
1
Figure 45.11 – Part 1
Chapter 45: Sensory Systems
figure 45-11b.jpg
Figure 45.11
– Part 2
Figure 45.11 – Part 2
Chapter 45: Sensory Systems
Mechanoreceptors: Detecting
Stimuli that Distort Membranes
• Hair cells are responsible for mammalian
auditory sensitivity.
• Ear pinnae collect and direct sound waves
to the tympanic membrane, which vibrates
in response to sound waves.
• The vibrations are amplified through a chain
of ossicles that conduct them to the oval
window.
• Movements of the oval window create
pressure waves in the fluid-filled cochlea.
Review Figure 45.12, 45.13
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Chapter 45: Sensory Systems
figure 45-12a.jpg
Figure 45.12
– Part 1
Figure 45.12 – Part 1
Chapter 45: Sensory Systems
figure 45-12b.jpg
Figure 45.12
– Part 2
Figure 45.12 – Part 2
Chapter 45: Sensory Systems
figure 45-12c.jpg
Figure
45.12 – Part
3
Figure 45.12 – Part 3
Chapter 45: Sensory Systems
Mechanoreceptors: Detecting
Stimuli that Distort Membranes
• The basilar membrane running down the center of
the cochlea is distorted at specific locations
depending on the frequency of the pressure wave.
• These distortions cause bending of hair cells in the
organ of Corti, which rests on the basilar
membrane.
• Changes in hair cell receptor potentials create
action potentials in the auditory nerve, which
conducts the information to the CNS.
Review Figure 45.13
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Chapter 45: Sensory Systems
figure 45-13.jpg
Figure 45.13
Figure 45.13
Chapter 45: Sensory Systems
Photoreceptors and Visual
Systems: Responding to Light
• Photosensitivity depends on the capture of
photons of light by rhodopsin.
• Rhodopsin is a photoreceptor molecule
consisting of opsin and retinal.
• Absorption of light by retinal is the first step
in a cascade of intracellular events leading
to a change in the receptor potential of the
photoreceptor cell.
Review Figure 45.15
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Chapter 45: Sensory Systems
figure 45-14.jpg
Figure
45.14
Figure 45.14
Chapter 45: Sensory Systems
figure 45-15.jpg
Figure
45.15
Figure 45.15
Chapter 45: Sensory Systems
Photoreceptors and Visual
Systems: Responding to Light
• When excited by light, vertebrate
photoreceptor cells hyperpolarize and
release less neurotransmitter onto neurons
with which they form synapses.
• They do not fire action potentials.
Review Figures 45.16, 45.17, 45.18
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Chapter 45: Sensory Systems
figure 45-16.jpg
Figure
45.16
Figure 45.16
Chapter 45: Sensory Systems
figure 45-17a.jpg
Figure 45.17
– Part 1
Figure 45.17 – Part 1
Chapter 45: Sensory Systems
figure 45-17b.jpg
Figure
45.17 –
Part 2
Figure 45.17 – Part 2
Chapter 45: Sensory Systems
Photoreceptors and Visual
Systems: Responding to Light
• Vision results when eyes focus patterns of
light onto layers of photoreceptors.
• The simple eye cups of flatworms can sense
the direction of a light source
• The compound eyes of arthropods can
detect shapes and patterns
• The eyes of cephalopods and vertebrates
have lenses.
Review Figures 45.18, 45.19, 45.20
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Chapter 45: Sensory Systems
figure 45-18.jpg
Figure
45.18
Figure 45.18
Chapter 45: Sensory Systems
figure 45-19.jpg
Figure 45.19
Figure 45.19
Chapter 45: Sensory Systems
figure 45-20.jpg
Figure 45.20
Figure 45.20
Chapter 45: Sensory Systems
Photoreceptors and Visual
Systems: Responding to Light
• The eyes of vertebrates and cephalopods
focus detailed images of the visual field onto
dense arrays of photoreceptors that
transduce the visual image into neural
signals.
Review Figure 45.21
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Chapter 45: Sensory Systems
figure 45-21.jpg
Figure
45.21
Figure 45.21
Chapter 45: Sensory Systems
Photoreceptors and Visual
Systems: Responding to Light
• The vertebrate photoreceptors are rod and
cone cells.
• Rod cells are responsible for dim light and
black-and-white vision
• Cone cells are responsible for color vision by
virtue of their spectral sensitivities.
Review Figure 45.23
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Chapter 45: Sensory Systems
Photoreceptors and Visual
Systems: Responding to Light
• The vertebrate retina is a dense array of neurons
lining the back of the eyeball.
• It consists of five layers of cells.
• The outermost layer consists of rods and cones.
• The innermost layer consists of ganglion cells,
which send their axons in the optic nerve to the
brain.
• Between the photoreceptors and ganglion cells are
neurons that process information from the
photoreceptors.
Review Figure 45.24
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Chapter 45: Sensory Systems
figure 45-24.jpg
Figure
45.24
Figure 45.24
Chapter 45: Sensory Systems
Photoreceptors and Visual
Systems: Responding to Light
• The area of the retina that receives light
from the center of the visual field, the
fovea, has the greatest density of
photoreceptors.
• In humans it contains almost exclusively
cone cells, which are responsible for color
vision but not very sensitive in dim light.
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Chapter 45: Sensory Systems
Photoreceptors and Visual
Systems: Responding to Light
• Each ganglion cell is stimulated by light
falling on a small circular patch of
photoreceptors called a receptive field.
• Receptive fields have a center and a
surround, which have opposing effects on
the ganglion cell.
• If the center is excitatory, the surround is
inhibitory, and vice versa.
See fig.45.25
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Chapter 45: Sensory Systems
figure 45-25a.jpg
Figure
45.25 –
Part 1
Figure 45.25 – Part 1
Chapter 45: Sensory Systems
figure 45-25b.jpg
Figure
45.25 –
Part 2
Figure 45.25 – Part 2
Chapter 45: Sensory Systems
Sensory Worlds Beyond Our
Experience
• Many animals have sensory abilities that we
do not share.
• Bats echolocate
• Insects see ultraviolet radiation
• Pit vipers “see” infrared radiation
• Fish sense electric fields.
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