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CHAPTER 3 SENSORY SYSTEMS

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  1. CHAPTER 3SENSORY 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

  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 • Useventralthalamic nuclei that project to primary sensory cortices • Neurons processes only input from of one sensory modality

  20. Visual system Classical ascending pathwaysNon-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 frommore than one sense

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

  23. Processing after primary sensory cortices • Integration of input from different sensory systems occurs inassociation cortices • Parallel processing • Stream segregation

  24. The neocortex has six layers

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

  26. Maps Tonotopic Somatotopic

  27. SURFACE VIEW

  28. LOWER BODY IS REPRE-SENTED NEAR THE MIDLINE

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

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

  31. Parallel processingStream segregation

  32. Parallel processing: Cochlear nucleus

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

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

  35. Convergence of input to a secondary neuron

  36. Lateral inhibition

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

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

  39. Processing after primary sensory cortices • Integration of input from different sensory systems occurs inassociation cortices

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

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

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

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

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

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

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

  47. HEARING LEVEL AT 4 kHz NOISE IMMISSION LEVEL

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