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Chapter Seven- modules 2 & 3 7.2: The Mechanical Senses 7.3: The Chemical Senses Slide 2: The Mechanical Senses The Mechanical Senses senses responsive to change in pressure, bending, or other structural change in a receptor Past Chapter on movementstretch receptors & stretch reflexes This Chapter somatosensation: touch, pain, temperature vestibular sensation: position and movement of head (leads to corresponding adjustments in posture, eye movements) Slide 3: Vestibular Sensation TRY IT: “Jiggle head and read, Then Jiggle Book” Why is it easier to read when you jiggle head? Vestibular Organs- adjusts for direction, tilt of head 3 semicircular canals- 3 planes, sends APs to cerebellum & brain stem via crainial nerve 2 otolith organs- sensitive hairs on H & V axis Slide 4: Somatosensation: Sensation of the body Somatosensation- sensation of body and its movements light touch, deep pressure, shape, temperature, pain & position of joints Location of many SS receptors- Skin-the body’s largest organ. Free nerve endings- Pain Pacinian Corpuscle- Sudden compressions/vibration nerve surrounded by onion like exterior decr. NA+ resistance when bent… effect? Meissner- responds to low frequency vibes Ruffini- stretch of skin.. Krause’s end bulbs- soft touch, lips? Genital? Slide 5: Spinal Nerves: Sending SS to brain Touch info below head enters brain through spinal nerves (above head through the crainial nerves) 31 set of Spinal nerves Each set corresponds to a skin sensory area called “Dermatomes” As nerve info enters brain, heads toward the SS cortex it divides into specific paths handling different sensory info (deep pressure, touch.) recall laminae of the cortex (particularly layer IV for sensory info) Slide 6: PAIN- a healthy signal! Pain- multiple sensations Carried by unmyelinated or thinly myelinated axons to spinal cord (dull- thin axons, sharp- fat) what does this anatomic difference tell you about the nature of the neural transmission of pain signals? Release the NTR: Substance P & glutamate moderate-glutamate intense-glutamate and substance P – prolonged exposure-- tends to desensitize Capsaicin- mimics substance P “Ben Gay-like” applications These are not really painful applications, so how are they working? Gate Theory of Pain- Melzack & Wall (1965) Why do we rub the “boo-boo” to make it better because it works!! But why does it work though Gate Theory- why non-pain stimuli reduce pain. The spinal cord is an area of congregation of multiple sensory signals, but can only handle limited number simultaneously-- after that… THE GATE CLOSES. Transcutaneous Electrical Nerve Stimulation (TENS) example of TENS unit Accupuncture? (w/ Electrical Stimulation or heat stimulation) Slide 8: Reducing Pain- Physiology Analgesic drugs - reduce pain- (“analgesia”) e.g., Opiates like morphine-decrease substance P activity Regulation of pain through opioid systems periaqueductal grey endorphins inhibit substance-P release enkephalin & leuenkephalin opiate systems share space in brain with areas that release substance P. Dull pain vs. Sharp Pain larger cell bodies (sharp) apparently less affected by endorphin activity than smaller cell bodies (dull). Slide 9: Chemical Senses Chemical Sensitivity- The most basic sensory system primitive/single celled organisms to make critical survival “decisions” about eating (poisonous or not); mating (finding, signaling) In humans, major chemical sensitivities refer to Taste & Smell (Olfaction) Experiencing change in the Chemical Senses Label-line principle- receptors respond to a limited range of stimuli and send direct line to brain. Across-fiber pattern principle- receptors respond to range of stimuli and contribute toward an overall experience. Combined pattern of response = our experience (most vertebrate experience sense most stimuli in this manner) Slide 10: TASTY! Taste buds- areas in the papillae containing 2050 taste receptors sensitive to certain chemical information (taste qualities). [exper] Short life- 10-14 days. Aggregated in tip, back, & sides (not middle). Slide 11: Taste Receptors Strong evidence for presence of 4 distinct dimensions of taste located somewhat discrete locations. 1) taste adaptation adaptation to one taste (e.g., sour) leads to decreased sensations of later sourness. 2) No cross-adaptation adaptation of one taste (sweet) does not affect another (salty). Taste- carried by 3 crainial nerves to NTS in brain helps to code meaning of taste (function,need). Gatorade after workout. Chemical Senses-Coding Taste Mechanisms & Patterning INOTROPIC EFFECTS Saltiness- receptor membrane salty receptors permeable to sodium (NA+) leading to excess positive ions in neuron and subsequent AP. Sourness- receptor at sour receptors prevent K+ release when an acidic substance binds to the receptor leading to excess positive ions in cell and subsequent AP. METABOTROPIC EFFECTS Sweetness & Bitterness- effect G-Protein action when substance binds to the receptor. Absence of this protein, absence of these tastes. KEY POINT: Buds sensitive to non-primary tastes ALSO, not completely discrete. Supports patterned principle. Chemical Senses OLFACTION- Structure Olfactory Bulb Olfactory Nerve Olfactory Nerve Axons Nasal Cavity Olfactory receptor cell Supporting cells Olfactory Cilia Chemical Senses Many Olfactory Receptors Hundreds (Thousands?) of olfactory receptor types may exist. Many similar receptor “families” with slightly different amino acid compositions therefore responsive to different odorant molecules. Effect, we smell with greater precision Why so many? Not that way with sight (3 receptors) Independence of chemistry of smell light - change in wave length, smell, completely different particles space- receptor take up space, more types more room needed. The Chemical Senses Vomeronasal Sensation and Pheromones Pheromones are chemicals released by an animal that affect the behavior of other members of the same species Human body secretions have subtle pheromone effects The human vomeronasal organ This organ detects certain chemicals, especially those found on the human skin, but produces no conscious experience. Perhaps for that reason, researchers were slow to discover this organ. Slide 16:
