Sensory receptor

1. MO Figure
Sensory Receptors
and the CNS
Perennou Nuridsany/Science Source.

2. Sensory pathways
Involve four steps
• Sensory reception: sensory receptors
detect a stimulus
• Sensory transduction: in response to
the stimulus, ion channels open or close,
which changes the membrane potential
• Transmission: an action potential is
carried to the CNS
• Perception: awareness of the stimulus
occurs in the brain.

3. Figure 1
Sensory reception

4. Figure 1a

5. Figure 1b

6. Figure 2
Amplification
Amplification is the
process through which a
signal is strengthened;
often involves signal
transduction pathways.

7. Figure 2a

8. Figure 2b

9. Sensory perception
Integration: several weak stimuli are added into one
large perceived stimulus. Occurs at several steps:
• During signal transduction, separate stimuli are
added together to generate an action potential.
• During transmission, several rapid action potentials
are integrated into one.
• In the CNS, signals from multiple sensory cells are
integrated into one signal.

10. Sensory adaptation
Sensitivity of sensory receptors changes
in response to constant stimulation
• Enables an animal to adjust to
changing environmental conditions.
• Enables an animal to ignore constant
stimuli that might otherwise be
distracting.

11. Types of sensory receptor
• Mechanoreceptors
• Chemoreceptors
• Electromagnetic receptors
• Thermoreceptors
• Nociceptors (pain receptors)

12. Mechanoreceptors
• Respond to mechanical stimulation, such
as pressure and sound.
• Responsible for senses of touch and
hearing
• Ion channels open or close in response to
deformation or movement.

13. Figure 3
Skin mechanoreceptors
Sensory
receptors in the
skin and
surrounding hair
follicles respond
to pressure.

14. Figure 4
Lateral line system
Used to sense movement
of water.

15. Figure 4a

16. Figure 4b

17. Chemoreceptors
Bind chemicals, responsible for senses of taste
and smell.
Olfaction: sense of smell, involves detection of
airborne chemicals called odorants.
Gustation: sense of taste, involves detection of
dissolved chemicals called tastants.
Aquatic animals do not have distinct senses of
taste and smell.

18. Figure 5
Pheromones
for navigation
Lampreys detect
pheromones secreted
by the larvae of their
species to navigate to
breeding sites.
(a) Jacana/Science Source. (b)
Gary Meszaros/Science Source.

19. Electromechanical receptors
• Detect electromagnetic energy such as light,
electricity, and magnetism
• Photoreceptors detect light and are responsible for
vision.
Visual organs:
Eyespots (planaria): sense light and dark
Compound eyes (insects): detect motion.
Single-lens eyes (vertebrates and some invertebrates):
focus image.

20. Figure 6
Photoreception
Planaria move away from light sources using
photosensitive eyespots.

21. Figure 7
Electromagnetic reception
Monarch butterflies
use magnetite to orient
themselves with
respect to Earth’s
magnetic field and
navigate during winter
migrations.
Courtesy of Gene Nieminen/USFWS.

22. Thermoreceptors
Sense changes in temperature

23. Nociceptors
(pain receptors)
• Detect injurious stimuli such as extreme
heat, pressure, and dangerous chemicals.
• In humans, many nociceptors are naked
dendrites of other types of receptors;
thermoreceptors, mechanoreceptors, and
chemoreceptors can act as nociceptors.

24. MO Figure Auditory and
Balance System
Courtesy of B. Peterson/USFWS.

25. Figure 1
The Auditory System

26. Figure 2
The Cochlea
Primary site of auditory sense reception. Contains
the fluid-filled vestibular and tympanic canals.
Vibration of the basilar membrane causes cilia on
hair cells to bend. Signals are transmitted to the
brain through the auditory nerve.

27. Figure 2a

28. Figure 2b

29. Figure 2c

30. Figure 3
Hair
cells
Bend back and forth in
response to fluid
movements from sound
waves. The bending
movements are translated
into neural signals that are
transmitted to the brain.
© 2004 Nature Publishing Group Modified from Frolenkov, G. I., et al., Genetic insights
into the morphogenesis of inner ear hair cells. Nature Reviews Genetics 5, 489–498
(2004) doi:10.1038/nrg1377. Used with permission.

31. Figure 4
Mechanism
of hearing

32. Figure 4a

33. Figure 4b

34. Figure 4c

35. Figure 5
Mechanism of hearing
The basilar
membrane
gets thinner
and more
flexible
toward the
center of the
cochlea.

36. Figure 5a
Mechanism of hearing

37. Figure 5b
Mechanism of hearing
The basilar membrane gets thinner and more
flexible toward the center of the cochlea.

38. Figure 6
The balance systems

39. Figure 6a

40. Figure 6b

41. Figure 6c

42. Figure 7
Semicircular canals
© 2007 Nature Publishing Group Sanlaville D. & Verloes, A. CHARGE syndrome: an update. European Journal of
Human Genetics 15, 389–399 (2007) doi:10.1038/sj.ejhg.5201778. Used with permission.
Clearly visible in normal newborns (left) and
missing in CHARGE affected newborns (right).

43. MO Figure
Vision
Courtesy of Gary M. Stolz/USFWS.

44. Figure 1
Eyespots
Planaria have primitive eyespots with
photosensitive tissue.
Eric V. Grave/Science Source.

45. Figure 2
Compound eyes
Thomas Shahan/Science Source.
Contain many ommatidia, each with its own
lens. Highly sensitive to motion.

46. Figure 3
Eye and retina anatomy

47. Figure 3a

48. Figure 3b

49. Figure 4
Microscope vs. eyes
Both have lenses that refract light.
Both can focus an image.
Both have an iris that adjusts light
levels.

50. Figure 4a

51. Figure 4b

52. Figure 5
Myopia, hyperopia,
and astigmatism
Abnormal curvature of the lens or cornea results
in light focusing incorrectly on the retina.

53. Figure 5a

54. Figure 5b

55. Figure 5c

56. Figure 6
Retinal
neurons
Several types of neurons in
the retina communicate with
each other to refine, sharpen,
and process visual stimuli.
These include bipolar cells
(green), rod photoreceptors
(red/purple), cones, amacrine
cells, ganglion cells, and
others.
© 2010 Nature Publishing Group Markus, A. Speedy rod
signaling. Nature Neuroscience 13, 410 (2010)
doi:10.1038/nn0410-410. Used with permission.

57. Figure 7
Visual processing
Although images are inverted at the retina, the visual cortex of the
brain reorients the images properly.

58. MO Figure
Taste and Smell
Picture Partners/Science Source.

59. Figure 1
Chemoreceptors
Robert Noonan/Science Source.
Insects have olfactory receptors that are typically
found on their antennae. Gustatory receptors can
be found on mouthparts and legs.

60. Figure 2
Taste buds
Associated
with papillae of
the tongue.
Contain cells
that detect
sweet, salty,
bitter, sour, and
umami (savory)
tastes.

61. Figure 2a

62. Figure 2b

63. Figure 2c

64. Figure 3

65. Figure 4
Olfaction
Greg Dimijian/Science Source.
Skunks use odorants for defense.

66. Figure 5
The
olfactory
pathway
Binding of odorants
to chemoreceptor
neurons triggers
action potentials that
are transmitted to
the olfactory bulb
and brain.

67. Figure 5a

68. Figure 5b