Tactile Sensation and Proprioception.txt

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Tactile Sensation and Proprioception.txt
2010-12-05 01:15:24

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  1. Tactile Sensation and Proprioception
    • Sensory stimuli - light touch, vibration, and proprioception
    • discriminative or two-point touch is an important collective property of this pathway
  2. Types of receptors
    • cutanous mechanoreceptors: Meissner's, Pacinian, Ruffini Corpuscles, Merkel receptors, hair receptors
    • Muscle and skeletal mechanoreceptors: muscle spindles, joint capsule receptors, Golgi Tendon Organ
  3. Cutaneous mechanoreceptors differ in
    • location in the skin : hairy vs non-hairy; superficial vs. deep
    • Receptive field: size of skin area
    • Adaptation: duration of action potential activity in their axons
  4. stereognosis
    • when several different types of receptors are activated simultaneously
    • collectively info is processed by synaptic interactions in the cortex to enable us to identify objects based on tactile sensation
  5. Primary axon diameters of mechanoreceptors
    • alpha: 10-20um
    • beta: 5-15um
    • gamma 3-10um
  6. First-Order neuron cell body/Nucleus
    Dorsal Root Ganglion (DRG)
  7. Second-Order neuron cell body/Nucleus
    Nuclei: Gracilis (lower body above and below T6, below T6 lower body ONLY) and Cuneatus (upper body above T6)
  8. Third-Order neuron cell body/Nucleus
    Ventral posterior Lateral (VPL) nucleus in the thalamus
  9. First-Order neuron axon/tract
    spinal nerve/fasciculus gracilis and cuneatus
  10. Second-Order neuron axon/tract
    Medial lemniscus (turns as go up like "elbows/forearms"
  11. Third-Order neuron axon/tract
    posterior limb of the internal capsule
  12. primary axons branch as they enter the spinal cord
    • pathway to cortex for sensory perception
    • locatl connections in spinal cord for reflexes
  13. Cortical localization of tactile sensation and proprioception
    • postcentral gyrus: is somatosensory cortex
    • also paracentral lobule
  14. loss of any of the complex tactile functions while simple, peripheral tactile awareness is intact
    agnosia: indicates a parietal cortex lesion
  15. Different tactile agnoaias
    • loss of 2-point discrimination
    • astereognosis
    • agraphesthesia
    • extinction on double simultanous stimulation - damage to the parietal lobe can cause misperception of or inattention to tactile stimuli
  16. a lesion
    • an area of localized dysfunction in the nervous system
    • May be caused by: trauma, loss of blood supply, tumors, congenital malformations, genetic disorders, viral and bacterial infection, disease, etc.
    • lesions typically block conduction/function, but in some situations they can irritate adjacent tissue and inched activity (e.g. seizures)
  17. loss of tactile sensibility: lesion could be in
    • spinal cord
    • brainstem
    • thalamus
    • internal capsule
    • postcentral gyrus
  18. 5 deficits: key symptoms that imply damage to the cortex
    • inability to localize tactile stimuli
    • loss of 2-point discrimination
    • astereognosis
    • agraphesthesia
    • extinction on double simultanous stimulation (inattention to bilateral stimuli)