classnotes12 - Nervous system, part II - sensory input....

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Nervous system, part II - sensory input. Overview: - sensory neurons are designed to register certain chemical, physical, or electrical events (this is broken down further below). - if the stimulus is strong enough, this sets off an action potential. - this impulse is then transmitted to the appropriate part of the nervous system. The perception of “light”, “sound”, etc. is not determined by the “receptor”, but rather on how/where the signal winds up (mostly in the brain). - silly, but suppose we could unplug nerves coming from eyes, plug in nerves coming from ears. Now sound would be registered as “light”, but who knows what it would be interpreted as. Sensory receptors - types: - 5 categories - mechanoreceptors - pain receptors - thermoreceptors - chemoreceptors - electromagnetic receptors [This list has nothing to do with the proverbial “5 senses”]. 1) mechano, pain & thermo receptors: - A lot of these come together in the skin. [Fig. 29.3A, p. 590 (not very good figure, though) ] . - touch is actually made up of several different receptors, most of which are sensory neurons (which wind up in the CNS). - pain - very important --> causes negative reaction --> move away from stimulus - leprosy (among other things, shuts down various pain receptors) - touch - several different categories - some sense deep touch (i.e.,sitting down) - light touch (often assisted by hairs) - light touch - detect air currents. - heat/cold (separate) sensors for heat or cold are not necessarily evenly distributed (for example, the chest has an excess of cold
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receptors). - also note that overall these mechanoreceptors are not evenly distributed throughout the body. There are more in the fingertips and other “sensitive” areas, and fewer along the back and similar areas. - hearing/equilibrium - sound is mechanical. Vibrations of air molecules are responsible for sound transmission. These vibrations are picked up by the appropriate structures. - Ear (mostly as in mammals) [OVERHEAD, fig. 29.4A-C, p. 592 - 593] : - outer ear; three parts: - pinna (collects, channels sound) - auditory canal (funnels sound to the eardrum) - eardrum (takes sound and pushes against the malleus) - middle ear: - malleus (or hammer) transmits vibrations to the: - incus (or anvil), which transmits sound to the: - stapes (or stirrup). - purpose --> sound amplification. These three little bones work together to mechanically amplify the sound. - the stapes conducts sound to the inner ear through the
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classnotes12 - Nervous system, part II - sensory input....

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