neurobio 917 ch 12 of Bear's book: the somatic sensory system part 2 (Pacinian corpuscle, two-point
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the axons of the dorsal column nuclei ascend within a conspicuous white matter tract called the ____ _______. Describe this structure
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
somatic sensation of the face is supplied mostly by the large _____ _______
the primary somatosensory cortex (S1) is located in which area of the brain?
it is located in Brodmanns area 3b
which areas of the cortex receive dense inputs from area 3b? What types of info. do they receive?
areas 1 and 2 receive dense inputs from area 3b. The projection from 3b to area 1 sends mainly texture info., while the projection to area 2 emphasizes size and shape.
what two similarities are there between the somatosensory cortex and other regions of cortex?
as is the case with the visual and auditory cortex, the thalamic inputs to S1 terminate mainly in layer IV. The neurons of layer IV, in turn, project to cells in the other layers. Another important similarity with other regions of cortex is that S1 neurons with similar inputs and responsses are stacked vertically into columns that extend acros the cortical layers.
what is somatotopy?
the mapping of the body's surfae sensations onto a structure in the brain is called somatotopy.
what are the two most sensitive parts of the body to somatic sensation?
the mouth, tongue, and hands
what is agnosia?
the inability to recognize objects even though simple sensory skills seem to be normal
explain briefly what the posterior parietal cortex does
Its neurons have large receptive fields, with stimulus preferences that are a challenge to characterize because they are so elaborate. Moreover, the area is concerned not only with somatic sensation but also with visual stimuli and movement planning
what is the difference between pain and nociception?
pain is the feeling, or perception, of irritating, sore, etc. Nociception is is the sensory process that provides signals that trigger pain
what kinds of stimuli may cause nociception>
nociception is caused by stimuli that have the potential to cause tissue damage. Tissue damage can result from strong mechanical stimulation, extremes in temp. , oxygen deprivation, and exposure to certain chemicals
what is hyperalgesia?
it is an example of our body's ability to control its own pain. Hyperalgesia can be a reduced threshold for pain, an increased intensity of painful simuli, or even spontaneous pain.
what is the difference between primary and secondary hyperalgesia?
primary hyperalgesia occurs within the area of the damaged tissue, but tissues surrounding a damaged area may become supersensitive as well by a process of secondary hyperalgesia
what is a polymodal nociceptor?
a nociceptor that responds to mechanical, thermal, and chemical stimuli
what is first pain and second pain>
first pain is a fast, sharp feeling of pain that is followed by a duller, longer-lasting second pain
when the nociceptor fibers enter the dorsal horn of the spinal cord, the fibers branch immediately, travel a short distance up and down the spinal cord in a region called....
The zone of Lissauer
once the nociceptor fibers go through the zone of Lissauer, where do they synapse?
they then synapse on cells in the outer part of the dorsal horn in a region known as the substantia gelatinosa
what is the cause of first and second pain?
first pain is caused by the activation of Aδ fibers and second pain is caused by the activation of C fibers
what are three major difference between the pain and touch pathways?
first, they differ with respect to their nerve endings in the skin The touch pathway is characterized by specialized structures in the skin; the pain pathway has only free nerve endings.
Second, they differ with respect to the diameter of their axons. The tough pathway is swift anduses fat, myelinated Aβ fibers; the pain pathway is slow and uses thin, lightly myelinated Aδ fibers and unmyelinated C fibers.
Third, they differ with respect to their connections in the spinal cord. Branches of the Aβ axons terminate in the deep dorsal horn; the Aδ and C fibers branch, run within the zone of Lissauer, and terminate within the substantia gelatinosa.
explain the difference between the spinothalamic pain pathway and the dorsal column-medial lemniscal pathway
unlike the dorsal column-medial lemniscal pathway, the axons of the second-order neurons immediately decussate and ascend through the spinothalamic tract running along the ventral surface of the spinal cord
which part of the brain does the spinothalamic pathway synapse with?