neurobio 917 ch 12 of Bear's book: the somatic sensory system part 3 (Pacinian corpuscle two-point

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  1. explain the trigeminal pain pathway
    pain (and temperature) info from the face and head takes a path to the thalamus that is analogous to the spinal path. The small-diameter fibers in the trigeminal nerve synapse first on second order sensory neurons in the spinal trigeminal nucleus of the brain stem. The axons of these cells cross and ascend to the thalamus in the trigeminal lemniscus
  2. which brain structure do both the spinothalamic pathway and dorsal column-medial lemniscal pathway innervate (albeit different parts of the structure)?
    the thalamus
  3. what occurs in the dorsal column medial lemniscal pathway once info reaches the dorsal column nuclei?
    the info. decussates to the other side of the midline of the spinal cord and then the pathway synapses with the thalamus.
  4. after the spinothalamic pathway and and dorsal column-medial lemniscal pathway exit the thalamus, where do they go next?
    the cerebral cortex
  5. info in the spinothalamic pathway moves up the spinal cord via the ___ ______  _____
    lateral spinothalamic tract
  6. true or false? the spinothalamic tract and trigeminal lemniscal axons synapse over a wider region of the thalamus than thos of the medial lemniscus
  7. which parts of the thalamus does the spinothalamic tract innervate?
    some of the axons terminate in the VP nucleus, just as the medial lemniscal axons do, but the touch and pain systems still remain segregated there by occupying separate regions of the nucleus. Other spinothalamic axons end in the small intralaminar nuclei of the thalamus
  8. what is PAG?
    PAG is a region of the brain that has been implicated in pain suppression
  9. if heat is applied to a large area of skin, it is usually painful; but if the heat is restricted to a small region of skin innervated by a cold receptor, what occurs? Why?
    it can produce a paradoxical feeling of cold. This phenomenon emphasizes an important point: the CNS does not know what kind of stimulus (in this case, heat) caused the receptor to fire, but it continues to interpret all activity from its cold receptor as a response to cold.
  10. explain the temperature pathway
    the temperature pathway is virtually identical to the pain pathway. Cold receptors are coupled to Aδ and C fibers, while warm receptors are coupled only to C fibers.
  11. if the spinal cord is transected only on one side, what resulting losses will occur and where?
    if the spinal cord is transected on one side, there will be aloss of temperature and pain sensitivity on the opposite side of the body and there will be a loss of tactile sensitivity on the same side of the the transection (below the cut)
  12. true or false? cold and hot (non-pain) sensation is mediated by the same receptors
    false. there are different receptors for various ranges of temperatures. (ex. Trpm8 is activated by nonpainful decreases in temperature below 25 degrees C)
  13. what kind of brain lesion causes neglect syndrome?
    a lesion of the parietal cortex
  14. what do Pacinian receptors do?
    they are sensitive to vibrations of about 200-300 Hz
  15. what do Meissner's corpuscles do?
    they are sensitive to vibrations of about 50 Hz
  16. Imagine rubbing your finger across a pane of smooth glass and then across a brick. What kinds of skin receptors help you distinguish the two surfaces? As far as your somatic sensory system is concerned, what is different about the two surfaces?
    Smooth glass might produce a stimulus with no vibrations and no changes in pressure. To detect this surface, mechanoreceptors, such as Merkel’s disks or Meissner’s corpuscles, should be close to the surface of the skin. To be detected, the stimulus that glass creates would have to excite slowly adapting mechanoreceptors because its surface does not change. Merkel’s disks are slowly adapting and have small receptive fields. A brick might produce a stimulus with vibrations and changes in pressure related to the raised parts of its surface. This is a good stimulus for the Pacinian corpuscles and Ruffini’s ending. To detect the successive peaks and valleys on the surface of the brick, a rapidly adapting receptor might best detect the stimulus. This requirement might make a Pacinian corpuscle the ideal receptor for this stimulus because Pacinian corpuscles are rapidly adapting, whereas Ruffini’s endings are slowly adapting.
  17. At what levels of the nervous system are all types of somatic sensory information represented on the contralateral side: the spinal cord, the medulla, the pons, the midbrain, the thalamus, the cortex?
    Information from the dorsal columns crosses at the level of the medulla after synapsing in the dorsal column nuclei, so dorsal column information is contralateral as it courses through the medial lemniscus to synapse in the thalamus and then in the cortex. The trigeminal touch pathway crosses at the level of the pons to synapse contralaterally in the VP nucleus of the thalamus. Information in the spinothalamic tract crosses early, at the level of the spinal cord, so all its information is contralateral by the time the afferents reach their targets in the thalamus. As a result, all types of somatic sensory information are represented on the contralateral side at the level of the thalamus
  18. Where in the CNS do information about touch, shape, temperature, and pain converge?
    The posterior parietal cortex is the area where segregated streams of somatosensory information converge to generate complex neural representations. Neurons in this cortical area have large receptive fields with stimulus preferences that are a challenge to characterize because they are so elaborate. This area is also concerned with visual stimuli and movement planning. Lesions in this area can result in agnosia, the inability to recognize objects even though simple sensory skills are normal. The posterior parietal cortex is essential for the perception and interpretation of spatial relationships, accurate body image, and the learning of tasks involving coordination of the body in space, all of which involve input from the visual system.
  19. what are the structures involved in in the dorsal column-medial lemniscal pathway (from beginning to end)?
    the primary sensory neurons receive the signal. These neurons then send info (ipsilaterally) through the dorsal roots into the spinal cord, up the dorsal columns. the axons of the dorsal column terminate in the dorsal column nuclei, which lie at the junction of the spinal cord and medulla. 

    Axons from cells of the dorsal column nuclei arch toward the ventral and medial medulla and decussate. From this point onward, the somatic sensory system of one side of the brain is concerned with sensations deriving from the other side of the body

    The axons of the dorsal column nuclei ascend within a white matter tract called the medial lemniscus. The medial lemniscus rises through the medulla, pons, and midbrain, and its axons synapse upon neurons of the ventral posterior nucleus of the thalamus. Thalamic neurons of the VP nucleus then project to specific regions of primary somatosensory cortex, or S1.
  20. true or false? S1 neurons with similar inputs and responses are stacked vertically into columns that extend across the cortical layers
  21. describe, in detail, the path that info takes in the spinothalamic pathway
    the info travels along the dorsal root axon into the spinal cord. The info. decussates immediately. The info ascends the lateral spinothalamic tract to the thalamus. From there, info is projected to the primary somatosensory cortex.
  22. what are the two temperature receptors that detect chemicals found in mint and hot peppers, respectively?
    • hot peppers- Trpv1
    • mint-Trpm8
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neurobio 917 ch 12 of Bear's book: the somatic sensory system part 3 (Pacinian corpuscle two-point
neurobio 917 ch 12 of Bear's book: the somatic sensory system part 3 (Pacinian corpuscle, two-point discrimination, touch, spinal segment, dermatome, dorsal column, nociception, spinothalamic pain pathway) #25
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