Table of Contents

1
CHAPTER 45Sensory Systems
2
Chapter 45 Sensory Systems

• Sensory Cells, Sensory Organs, and Transduction
• Chemoreceptors Responding to Specific Molecules
• Mechanoreceptors Detecting Stimuli that Distort
  Membranes

3
Chapter 45 Sensory Systems

• Photoreceptors and Visual Systems Responding to
  Light
• Sensory Worlds Beyond Our Experience

4
Sensory Cells, Sensory Organs, and Transduction

• Sensory cells transduce information about an
  animals external and internal environment into
  action potentials.
• Review Figures 45.1, 45.2
• 4

5
Figure 45.1 Part 1
figure 45-01a.jpg

• Figure 45.1 Part 1

6
Figure 45.1 Part 2
figure 45-01b.jpg

• Figure 45.1 Part 2

7
Figure 45.2
figure 45-02.jpg

• Figure 45.2

8
Sensory Cells, Sensory Organs, and Transduction

• The interpretation of action potentials as
  particular sensations depends on which neurons in
  the CNS receive them.
• 8

9
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
• 9

10
Figure 45.3
figure 45-03.jpg

• Figure 45.3

11
Sensory Cells, Sensory Organs, and Transduction

• Adaptation enables the nervous system to ignore
  irrelevant stimuli while remaining responsive to
  relevant or to new stimuli.
• 11

12
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
• 12

13
Figure 45.5
figure 45-05.jpg

• Figure 45.5

14
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.
• 15

15
Chemoreceptors Responding to Specific Molecules

• Chemoreceptors in the mouth cavities of
  vertebrates are responsible for the sense of
  taste.
• Review Figure 45.6
• 16

16
Figure 45.6
figure 45-06.jpg

• Figure 45.6

17
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
• 18

18
Figure 45.7
figure 45-07.jpg

• Figure 45.7

19
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
• 20

20
Figure 45.8
figure 45-08.jpg

• Figure 45.8

21
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
• 22

22
Figure 45.9
figure 45-09.jpg

• Figure 45.9

23
Figure 45.10
figure 45-10.jpg

• Figure 45.10

24
Figure 45.11 Part 1
figure 45-11a.jpg

• Figure 45.11 Part 1

25
Figure 45.11 Part 2
figure 45-11b.jpg

• Figure 45.11 Part 2

26
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
• 29

27
Figure 45.12 Part 1
figure 45-12a.jpg

• Figure 45.12 Part 1

28
Figure 45.12 Part 2
figure 45-12b.jpg

• Figure 45.12 Part 2

29
Figure 45.12 Part 3
figure 45-12c.jpg

• Figure 45.12 Part 3

30
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
• 31

31
Figure 45.13
figure 45-13.jpg

• Figure 45.13

32
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
• 33

33
Figure 45.14
figure 45-14.jpg

• Figure 45.14

34
Figure 45.15
figure 45-15.jpg

• Figure 45.15

35
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
• 35

36
Figure 45.16
figure 45-16.jpg

• Figure 45.16

37
Figure 45.17 Part 1
figure 45-17a.jpg

• Figure 45.17 Part 1

38
Figure 45.17 Part 2
figure 45-17b.jpg

• Figure 45.17 Part 2

39
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
• 40

40
Figure 45.18
figure 45-18.jpg

• Figure 45.18

41
Figure 45.19
figure 45-19.jpg

• Figure 45.19

42
Figure 45.20
figure 45-20.jpg

• Figure 45.20

43
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
• 43

44
Figure 45.21
figure 45-21.jpg

• Figure 45.21

45
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
• 45

46
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
• 47

47
Figure 45.24
figure 45-24.jpg

• Figure 45.24

48
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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49
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
• 51

50
Figure 45.25 Part 1
figure 45-25a.jpg

• Figure 45.25 Part 1

51
Figure 45.25 Part 2
figure 45-25b.jpg

• Figure 45.25 Part 2

52
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.
• 52