sensory system.ppt
- 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
- 12. Sensory transduction (mechanoreceptor in a muscle)
- 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. From: Møller: Sensory Systems, 2003 Classical auditory pathways Non-classical auditory pathways
- 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. From: Møller, 2005 Visual system Classical ascending pathways Non-classical ascending pathways
- 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
- 26. Simplified diagram of the connections to and from the different layers of the cerebral cortex From: Møller: Sensory Systems, 2002
- 28. SURFACE VIEW
- 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
- 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
- 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. From: Møller: Sensory Systems, 2003 Stream segregation Cortical circuitry Dorsal stream “where” Ventral stream “what”
- 43. Sensory information can reach other regions than sensory regions Motor systems Memory Emotional brain (limbic system)
- 44. From: Møller, 2005 Two different routes to the Amygdala from a sensory system
- 45. From: Møller: Sensory Systems, 2003 Connections from a sensory system to the amygdala “the high route”
- 46. Connections from a sensory system to the amygdala “the low route” From: Møller: Sensory Systems, 2003
- 47. From: Møller: Sensory Systems, 2003 Connections from the amygdala
- 48. Hypoactive sensory disorders • Loss of sensitivity – Hearing loss – Poor vision – Numbness – Loss of vestibular (balance) function
- 51. Courtesy of M. Charles Liberman Genetic, epigenetic and environmental Causes (and a stochastic component ?)
- 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. 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”)
- 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