1. CHAPTER 3 SENSORY SYSTEMS

2. Disorders of sensory systems
Deficits
Sensory organ
Sensory nerves
Central nervous system
Hyperactivity
Central neuropathic pain
Tinnitus
Tingling
Normal response that is redirected
Pain from touch
Dizziness and vertigo from head movements

3. Disorders of sensory systems
Reduced sensitivity
Hearing loss
Visual impairment
Incorrect response
Hyperacusis
Distorted sounds
Allodynia
Hyperpathia

4. Disorders of sensory systems
Impaired conduction of the physical stimulus to the receptors
Impaired function of receptors
Impaired function of sensory nerves
Impaired or changed function of the central nervous system

5. Reduced sensitivity Often caused by disorders of the sense organs
Injury to afferent nerves

6. Hyperactive sensory disorders
Increased sensation of physical stimuli
Altered sensation of physical stimuli
Sensation without any physical stimulation

7. General organization of sensory systems
Conduction of the physical stimulus to the receptors
Sensory receptors
Sensory nerves
Central nervous system

8. Sensory transduction
A physical stimulus generates a receptor potential
The receptor potential is a graded potential
The receptor potential is conducted electrotonically to the spike generation site

9. Bipolar receptor cells (taste)

10. Initiation of nerve impulses
Occurs at the first node of Ranvier

11. Two different types of receptors, with bipolar nerve fibers
BRODAL 6.1

12. Sensory transduction (mechanoreceptor in a muscle)

13. Central nervous system

14. HUMAN
Mouse
Chick

15. Auditory nervous system Ascending auditory pathways
From: Møller, 2005

16. Two different ascending sensory pathways have been identified:
The classical systems
The non-classical systems

17. Classical auditory pathways Non-classical auditory pathways
From: Møller: Sensory Systems, 2003

18. Non-classical auditory pathways
Receive input from the somatosensory system
Use the dorsal part of the MGB
From: Møller, 2005

19. The classical ascending pathways
The number of nuclei is different in different sensory systems
Use ventral thalamic nuclei that project to primary sensory cortices
Neurons processes only input from of one sensory modality

20. Classical ascending pathways Non-classical ascending pathways
Visual system
Classical ascending pathways Non-classical ascending pathways
From: Møller, 2005

21. The nonclassical pathways
Use dorsal and medial thalamic nuclei that project to secondary cortices and to other parts of the CNS
Receive input from more than one sense

22. Somatosensory pathways Classical pathways Non-classical pathways
From: Møller, 2005

24. Processing after primary sensory cortices
Integration of input from different sensory systems occurs in association cortices
Parallel processing
Stream segregation

25. The neocortex has six layers

26. Simplified diagram of the connections to and from the different layers of the cerebral cortex
From: Møller: Sensory Systems, 2002

27. Tonotopic Somatotopic
Maps
Tonotopic
Somatotopic

28. SURFACE VIEW

29. LOWER BODY IS REPRE-SENTED NEAR THE MIDLINE

30. Tonotopic organization in the CN of a cat, as an example of tonotopic organization in the auditory system

32. Tonotopic organization in the CN of a cat, as an example of tonotopic organization in the auditory system

33. Parallel processing Stream segregation

34. Parallel processing:
Cochlear nucleus

35. Function of sensory nervous systems
Processing of sensory input at the peripheral level
Convergence (spatial integration)
Interplay between inhibition and excitation

36. Spatial integration:
Receptive field of a
dorsal column nucleus cell

37. Convergence of input to a secondary neuron

38. Lateral inhibition

39. Central processing of sensory information
Each stage enhances or suppress specific Information

40. Parallel processing: The same information is processed in different structures Stream segregation: Different kinds of information is processed in different structures (“What” and “Where”)

41. Processing after primary sensory cortices
Integration of input from different sensory systems occurs in association cortices

42. Stream segregation Cortical circuitry
Dorsal stream
“where”
Ventral stream
“what”
From: Møller: Sensory Systems, 2003

43. Sensory information can reach other regions than sensory regions
Motor systems
Memory
Emotional brain (limbic system)

44. Amygdala from a sensory system
Two different
routes to the
Amygdala from a sensory system
From: Møller, 2005

45. Connections from a sensory system to the amygdala “the high route”
From: Møller: Sensory Systems, 2003

46. Connections from a sensory system to the amygdala “the low route”
From: Møller: Sensory Systems, 2003

47. Connections from the amygdala
From: Møller: Sensory Systems, 2003

48. Hypoactive sensory disorders
Loss of sensitivity
Hearing loss
Poor vision
Numbness
Loss of vestibular (balance) function

50. HEARING LEVEL AT 4 kHz
NOISE IMMISSION LEVEL

51. Genetic, epigenetic and environmental
Causes (and a stochastic component ?)
Gunea Pig PTS.
From: Maison, SF and Liberman, MC. Predicting vulnerability to acoustic injury with a non-invasive assay of olivocochlear reflex strength. J. Neurosci. 2000; 20:
males ( g); the exposure was a 2-4 kHz octave band of noise at 109 dB SPL for 4 hrs with a 1 week survival.
The mean peak PTS was 35.1 dB at 7.6 kHz (SD of dB)
Mice PTS:
Yoshida N and Liberman MC (2000) Sound conditioning reduces noise-induced permanent threshold shift in mice. Hearing Research 148:
males (23-29 g) exposed to octave band noise (8-16 kHz) at 100 dB for 2 hrs with a 1 week survival. The mean peak PTS was 38 dB at 17.5 kHz (SD of 4.06 dB).
Courtesy of M. Charles Liberman

52. Age-related
hearing loss

53. Normal variations in hearing loss of
70 year old individuals

54. Variations in speech discrimination in
70 year old individuals

55. Hearing loss in Ménière's disease

56. Effect of surgical injuries
to the auditory nerve:
Large decrease in speech
discrimination

57. Hyperactive sensory disorders
Tinnitus
Paresthesia
Phosphenes
Phantom sensations
Central neuropathic pain

58. Subjective and objective tinnitus
Different forms of tinnitus have very different effects on an individual’s life

59. Similarities between chronic pain and severe tinnitus

60. There are many forms of tinnitus
Mild tinnitus:
Does not interfere noticeably with everyday life
Moderate tinnitus:
May cause some annoyance and may be perceived as unpleasant
Severe tinnitus:
Affects a person’s entire life in major ways
Patients’ own perception varies between mild, moderate and severe (disabling)

61. Important to have words for disorders
We cannot think about matters that do not have names
The same words is used to describe very different forms of tinnitus and pain
Using the same names for fundamentally different disorders is a disadvantage in treating these disorders

62. How prevalent is severe tinnitus?
Some statistics show 50 million people have tinnitus in the USA
The prevalence of severe (bothersome) tinnitus is infrequent at young age; it reaches 12-14% for people at age 65 according to one study

63. How prevalent is severe pain?
Some pain was reported by 86% of individuals above the age of 65
(Iowa study, 1994)
The prevalence of severe pain was 33% for people at age 77 and above (Swedish study, 1996)

64. Severe tinnitus affects a person’s entire life in major ways
Prevents or disturbs sleep
Interferes with or prevents
Intellectual work
Often accompanied by altered perception of sound
        

65. Severe pain affects a person’s entire life in major ways
Prevent or disturb sleep
Interfere with or prevents intellectual work 
May cause suicide
  May involve limbic structures causing affective reactions
Often accompanied by abnormal sensations from touch

66. Severe tinnitus is often accompanied by altered perception of sound
Sounds are distorted
Sounds have exaggerated loudness (hyperacusis)
Sounds are unpleasant
Sounds are painful and arouse fear (phonophobia)

67. Little is known about the cause of subjective tinnitus
Noise exposure
Ototoxic antibiotic
Acoustic tumors

68. Some forms of tinnitus can be cured by sympathectomy
The sympathetic nervous system is involved in some forms of severe tinnitus
Some forms of tinnitus
can be cured by sympathectomy

69. Deprivation of sound can cause changes in neural processing such as change in temporal integration
Expression of neural plasticity

70. The anatomical location of the abnormality that cause chronic pain and tinnitus may be different from that to which the pain or the tinnitus is referred  

71. The abnormal neural activity that causes symptoms are not generated at the location where the symptoms are felt
Examples:
Phantom pain
Tinnitus with severed auditory nerve

72. The tinnitus in some patients can be modulated by stimulation of the somatosensory systems (such as by electrical stimulation of the median nerve) “cross-modal” interaction

73. Non-classical auditory pathways
Receive input from the somatosensory system
Use the dorsal part of the MGB
From: Møller, 2005

74. Other signs of involvement of the somatosensory system
Gaze related tinnitus
Neck muscles and tinnitus
TMJ and tinnitus
Sensation of sound from touching the skin

75. Connections between spinal C2 segment and the dorsal cochlear nucleus
Can explain why electrical stimulation of the skin behind the ears can modulate tinnitus

76. Symptoms and signs of neuropathic pain and severe tinnitus
Strong emotional components
Depression
High risk of suicide

77. Severe tinnitus is often associated with affective (mood) disorders
Depression
Phonophobia

78. The amygdala is involved in fear and other mood disorders

79. Connections from the auditory system to the amygdala
Cortical-cortical connections (the “high route”)
Subcortical connections
(the “low route”)

80. From: Møller, 2005

81. CONCLUSION
ACTIVATION OF NON-CLASSICAL ASCENDING SENSORY PATHWAYS CAN CAUSE SYMPTOMS AND SIGNS OF SEVERAL DISEASES

82. Neural plasticity play greater role in generating symptoms and signs than previously assumed
Plastic changes are reversible
Treatments without medicine and surgery may alleviate pain and tinnitus

83. Therapy
There is no treatment for tinnitus that is comparative to common pharmacological treatment of pain. Treatment of tinnitus has been mainly benzodiazepines (GABAA agonists)

84. Reversal of neural plasticity
“TENS” (transderm electric nerve stimulation) has been used for many years in treatment of chronic pain
Recently sound stimulation in various forms have been introduced in treatment of severe tinnitus

85. Stimulation of somatosensory system can relieve tinnitus
Electrical stimulation
of the ear and
of the skin behind the ears have been used to treat tinnitus
Electrical stimulation of the auditory cortex is in a stage of development
Few systematic studies of efficacy have been published