1. Sensory System
Transmits sensory information collected by receptors to the CNS

2. Outline 1- General principles of sensory physiology
2- The somatosensory System
3- Olfaction
4- Taste
5- Hearing and Equilibrium
6- Vision

3. Outline 1- General principles of sensory physiology
2- The somatosensory System
3- Olfaction
4- Taste
5- Hearing and Equilibrium
6- Vision

4. 1- General Principles of Sensory Physiology
Receptor physiology
Sensory pathways
Sensory coding

5. Sensory receptors Somatic Visceral
-- Chemoreceptors (taste, smell, smell)
-- Thermoreceptors (temperature)
-- Photoreceptors (vision)
-- Baroreceptors (sound, balance)
-- Proprioreceptors (muscle stretch)
Visceral
-- Chemoreceptors (chemicals in blood, osmoreceptors)
-- Baroreceptors (blood pressure)

6. Sensory transduction
Receptors transform an external signal into a membrane potential
Two types of receptor cells:
- a nerve cell
- a specialized epithelial cell

7. Two types of sensory receptors
Figure 10.2

8. Receptor adaptation Tonic receptors Phasic receptors
-- slow acting, -- no adaptation: continue to for impulses as long as the stimulus is there
(ex: proprioreceptors)
Phasic receptors
-- quick acting, adapt: stop firing when stimuli are constant (ex: smell)

9. Sensory coding
A receptor must convey the type of information it is sending  the kind of receptor activated determined the signal recognition by the brain
It must convey the intensity of the stimulus  the stronger the signals, the more frequent will be the APs
It must send information about the location and receptive field, characteristic of the receptor

10. Sensory pathways
The sensory pathways convey the type and location of the sensory stimulus
The type: because of the type of receptor activated
The location: because the brain has a map of the location of each receptor

11. Outline 1- General principles of sensory physiology
2- The somatosensory System
3- Olfaction
4- Taste
5- Hearing and Equilibrium
6- Vision

12. The Somatosensory System
Types of receptors
- Mechanoreceptors:
-- Proprioreceptors in tendons, ligaments
and muscles  body position
-- Touch receptors in the skin: free nerve endings, Merkel’s disks and Meissner’s corpuscles (superficial touch), hair follicles, Pacinian corpuscles and Ruffini’s ending
- Thermoreceptors: Warm receptors (30-45oC) and cold receptors (20-35oC)
- Nociceptors: respond to noxious stimuli
Figure 10.6

13. Skin touch receptors
Figure 10.13

14. Figure 10.15

15. Pain perception
Fast pain: sharp and well localized, transmitted by myelinated axons
Slow pain: dull aching sensation, not well localized, transmitted by unmyelinated axons
Visceral pain: not as well localized as pain originating from the skin  pain impulses travel on secondary axons dedicated to the somatic afferents  referred pain

16. Referred pain
Figure 10.16a

17. Figure 10.16b

18. What is Phantom pain?

19. Outline 1- General principles of sensory physiology
2- The somatosensory System
3- Olfaction
4- Taste
5- Hearing and Equilibrium
6- Vision

20. Olfaction
Specialized neurons present in the olfactory epithelium in the nose.
They project cilia into a mucus layer. The cilia are able to bind to odorant molecules  the binding triggers an AP which is transmitted to the olfactory area of the olfactory bulb  olfactory cortex (lower frontal area and limbic system of the brain
Each olfactory receptor is specialized for 1 odorant molecule

21. Outline 1- General principles of sensory physiology
2- The somatosensory System
3- Olfaction
4- Taste
5- Hearing and Equilibrium
6- Vision

22. Taste
Receptors for taste are modified epithelial cell present in taste buds located on the tongue, roof of the mouth and pharynx

23. Four primary types of taste receptors : sour, salt, sweet and bitter (and a new one: umami)
The binding of the receptor to a taste molecule triggers the entry of calcium in the cell  release of neurotransmitter in a synapse with a neuron

24. Taste receptors

25. Neural pathway
Taste impulses travel through nerves VII, IX and X to a gustatory nucleus in the medulla oblongata (cross over)  thalamus  gustatory cortex located in the parietal lobe in the mouth area.

26. What is the flavor of food?

27. Outline 1- General principles of sensory physiology
2- The somatosensory System
3- Olfaction
4- Taste
5- Hearing and Equilibrium
6- Vision

28. Hearing - Equilibrium
Figure 10.37

29. Hearing Sounds are waves of compressed air traveling through space
- sound intensity wave height
- pitch  wave frequency

30. Organ of hearing (and equilibrium) – inner ear
Cochlea
Vestibular apparatus

31. Hearing
1- The sound waves enter the external auditory canal and trigger vibrations of the tympanic membrane
2- The tympanic membrane induces a vibration of the ossicles
3- the last ossicle, the stapes, transmits amplified vibrations to the oval window
4- The vibrations induce waves in the perilymph of the various inner ear chambers
5- the round window absorbs excess energy and prevent wave reverberation
6- the fluid wave is transduced into an electrical signal by the auditory receptors, the organs of Corti located on the basilar membrane

32. Receptors for sound: the organ of Corti
The hair cells of the organ of Corti transduce fluid wave into an electrical signal
The energy of the wave causes the basilar and vestibular membrane to move, thus displacing the cilia from the organ of Corti

33. Signal transduction
Movements of the cilia open or close potassium channels  changes in the state of polarization of the hair cell
Changes in potassium leakage due to cilia bending trigger changes in neurotransmitters exocytosis
The neurotransmitters send an electrical signal to an afferent neuron of the cochlear nerve
The louder the sound, the more the cilia bend, the more numerous are the APs produced

34. Coding for pitch
The location of the organs of Corti on the basilar membrane codes for pitch
- Organs of Corti located near the oval window are more sensitive to high pitch sounds while the ones located toward the tip of the cochlea respond more readily to low pitch sound

35. Coding for sound intensity

36. Neural pathway for sounds
Cochlear nerve  nucleus in medulla oblongata  thalamus  auditory cortex in the temporal lobe
So, how do we perceive the direction from which a sound is coming from?

37. Equilibrium
Ability to detect head position and movement (or acceleration)
Change of speed = linear acceleration (utricle and saccule)
Turning = rotational acceleration (semi-circular canals)

38. Utricle and saccule
Sensory cells have cilia extending into a gelatinous material topped by otoliths
Saccule detects backward-frontward movement
Utricle detects changes relative to gravity

39. Figure 10.46a–c

41. Semi-circular canals
The receptors in the ampulla are hair cells with cilia extruding into a gelatinous mass (cupula)
When the head rotates, the cupula moves  cilia pulled APs (vestibular nerve  cerebellum …)

43. So why does a person become dizzy after he/she stops spinning?

44. Outline 1- General principles of sensory physiology
2- The somatosensory System
3- Olfaction
4- Taste
5- Hearing and Equilibrium
6- Vision

45. Vision

46. The eye can only perceive a small portion of the spectrum of electromagnetic waves

47. Vision In order to see an object:
- 1- the pattern of the object must fall on the vision receptors (rods and cones in the retina)  accommodation
- 2- the amount of light entering the eye must be regulated (too much light will “bleach out” the signals)
- 3- the energy from the waves of photons must be transduced into electrical signals
- 4- The brain must receive and interpret the signals

48. Accommodation
It is the process of adjusting the shape of the lens so that the external image fall exactly on the retina

49. Accommodation Object is far  the lens flattens
Object is near  the lens rounds
Figure 10.25

50. Accommodation abnormalities
Myopia
Hyperopia
Astigmatism: the cornea is irregular  irregular pattern of vision
Presbyopia: stiffening of the lens occurring with aging  increased difficulty with near vision

51. Figure 10.27a–b

52. Figure 10.27c

53. Regulation of the amount of light entering the eye
The iris controls the amount of light entering the eye cavities
The contraction of radial or circular smooth muscles located within the iris permit changes in the pupil diameter

54. Figure 10.28a

55. Eye abnormalities
Cataract
Glaucoma
Figure 10.27b

56. Retinal structure Three cell layers:
-- outer layer: photoreceptors- rods and cones
-- middle layer: bipolar neurons
-- inner layer: ganglion cells

57. Phototransduction
Photons hit the pigment of a photoreceptor    enzymes are activated in the cell which modify its state of polarization  the signals are sent to visual area of the occipital lobe of the brain through the optic nerve

58. Figure 10.31

59. Figure 10.33b

60. Neural processing
The bipolar neurons and ganglion cells process the signal
In the fovea where the acuity is the highest: 1 cone  1 bipolar cell  1 ganglion cell
At the periphery: many rods  1 bipolar cell … acuity is much decreased
Other cells in the retina participate in signal processing

61. Neural pathway
The right visual field maps on the left visual cortex and vice versa
Figure 10.36

62. Neural pathway What will happen if the left optic nerve is severed?
What will happen if a person has a tumor in the pituitary gland (just below the optic chiasmata) and the inner fibers are destroyed?
What will happen if a person suffers a brain tumor on the right side of the brain around the lateral geniculate body?

63. Depth of perception
The images from the 2 eyes are needed for depth of perception

65. Readings: Chp. 10, p. 253-301 Not expected:
Pain gate-control theory, p. 268.
Phototransduction, p