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Student.Questions.Recent.Lectures - Student Questions on...

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Student Questions on Recent Lectures [thanks to students submitting questions!] Chapter 8 Q. Why do the axons cross over to the opposite side of the spinal cord in fig. 8.1 and 8.6a? A. Both pain and tactile information end up in the opposite cerebral hemisphere—as does visual information as well. The pain/temp fibers cross at the spinal level while the other somatosensory fibers cross in the brainstem (medulla). I have no explanation for why the info crosses at these different levels, but the bigger question is why so much sensory information is conveyed to the opposite (contralateral) cerebral cortex. Unfortunately, there is no clear answer for this bigger question either! One kind of explanation would be that aversive responses (like the escape behavior) are generally going to be directed away from a stimulus, and so a contralateral representation/ organization might be useful in regards to producing contraversive responses. But it could work just as well without this crossing of the raw sensory information, by having the motor outputs cross. I have posted several references on BB under “course information”, titled brain asymmetries. Q. What would be an example of a slowly-adapting neuron? A. Merkel’s disks and Ruffini’s corpuscles are both listed in the text as slowly adapting which means that they have relatively sustained responses to stimuli impinging upon your skin. Rapidly adapting means the responses are very transient. This is a general strategy used to report both persistent environmental stimuli and to detect changing stimuli—e.g. retinal ganglion cells come in both transient and sustained types, while at different levels in central auditory processing we find cells that signal the onset of tones, while others signal their duration. Q. Do first-order neurons originate in the peripheral nervous system at the stimulus or do they originate in the brain?
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