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Unformatted text preview: Sensory Physiology II: Somatic, Vision Classify 3 types of receptors: 1. Mechanoreceptors sense pressure (vibration). EX: Pacinian Corpuscle and Meissners Corpuscle 2. Thermoreceptors sense change in skin temperature 3. Pain Receptors respond to pain There are also free nerve endings but they mostly deal with the thermoreceptors and pain receptors. 1. Mechanoreceptors Variability in vibration and pressure Meissner Corpuscles (RA) and Merkel Receptors (SAI) process stimuli from small areas points Pacinian Corpuscles (PC) can deal with broad regions of the hand or even whole fingers Ruffini Corpuscles (SAII) respond to stimuli that cause skin to stretch and are usually selective for the direction of the stretch. Left vibration, Right pressure Receptive Field Size vs. Adaptation rate Meissners Corpuscles (RA) have a small area and fast adaptation Merkels Disks (SAI) have a small area and slow adaptation Pacinian Corpuscles (PC) have a large area and fast adaptation Ruffinis Endings (SAII) have a large area and slow adaptation. EX: Pacinian Corpuscle extra lamella from epithelial cells wrap around the unmyelinated sensory terminal. There is an action potential only when the stimulus begins and when the stimulus ends. The axon is the same as that of a slow adapting cell and has a much longer response without the lamella so something in the lamella makes the response fast. 2. Thermoreceptors Some free endings and hybrid between phasic and tonic Cold receptor starts at 5 and has max at 20 Warm receptor starts around 30 degrees As temperature increases further, the warm receptor stops firing and the cold receptor begins again. Receptors normally flipflop until the temperature goes back to baseline. On and off responding and in middle 3. Pain Receptors stimulated by anything that breaks skin Cells release prostaglandins and bradykinin Signals released by free nerve endings react to the prostaglandins, bradykinin, and K+ and cause noxious signal The axon sends signals in three different directions 1. Substance P goes to blood vessels and smooth muscles causes vasodilation more blood into the area. 2. Substance P goes to the Mast cell (immune system cell) and makes it release Histamine. The Histamine further propagates the signal and also promotes swelling. 3. Causes a 2 nd noxious signal which goes to the spinal cord through the dorsal root ganglion 2 types of receptors o A Fiber myelinated o C Fiber - no myelin Pain is felt twice o First pain is sharp and is registered by noxious signals and mediated by the fast acting A axons....
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This note was uploaded on 05/01/2008 for the course BIOL 34 taught by Professor Velez during the Spring '07 term at Dartmouth.
- Spring '07