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CHAPTER 3 SENSORY SYSTEMS

CHAPTER 3 SENSORY SYSTEMS. 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.

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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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