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psych106-13 - Ves$bular and Somatosensa$on PSYC 106...

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Unformatted text preview: Ves$bular and Somatosensa$on PSYC 106 Feb 21—Lecture 13 EXAM ON THURSDAY! •  Covers lectures 9 ­13 (everything from Feb 7 through today) •  REVIEW SESSION: TOMORROW! –  In Pepper Canyon Hall room 122 –  At 7:00pm Lecture Outline 1.  Ves$bular Sensa$on –  balance 2.  Somatosensa$on –  Sensory receptors in the skin (joints/muscles) –  Segments of the spinal cord –  Somatosensory cortex in the brain 3.  Phantom Limbs 4.  Pain The Senses Electromagne$c Sense (1) Vision The Mechanical Senses (2) Audi$on (3) Somatosensa$on (TODAY) (6?) Ves$bular Sensa$on (TODAY) Chemical Senses: Molecules that Enter Your Body (4) Olfac$on (Smell) (5) Gusta$on (Taste) Don’t need to know Chemical Senses Ves$bular System •  Located in the Inner Ear and Comprised of: –  3 fluid filled semi ­circular canals—one for each plane –  Saccule: sensi$ve to linear mo$on –  Utricle: sensi$ve to gravity •  Remember, the inner ear is filled with FLUID •  Otoliths: calcium carbonate par$cles in the saccule and utricle –  When the head moves, they shig and bend the cilia on the hair cells •  Hair cells get depolarized (graded poten$al) •  Hair cells project to the Ves5bular Nerve Cells (VNC) (ac$on poten$al) -  Damage to the hair cellsver$go •  VNC axons project to the Ves5bular Nucleus of the brainstem -  Via the 8th cranial nerve (which also contains axons from auditory nerve cells which receive from the hair cells on the basilar membrane and project to the Cochlear Nucleus in the brainstem) Ves$bular Occular Reflex (VOR) •  General idea (which is all you need to know): ves$bular nerve sends signals to ocular nerves that move your eyes when your head moves, so the world stays in the same place on your re$na Cranial nerve 3 Cranial nerve 6 Some$mes you need to SUPPRESS your VOR, when that failsseasickness! Somatosensa$on •  Sensa$on of the body/skin and movements of the body •  Different receptors allow us to feel: –  Deep pressure –  Temperature –  Pain –  Itch –  Tickle –  And, iden$fy shape of objects (discrimina$ve touch) –  Detect the posi$on and movement of joints Somatosensory Receptor Types (Sensory Neurons) 1) Tac5le: response to being touched (“light” and “deep” touch) - Ruffini ending, Meissner’s corpuscle, Pacinian corpuscle - The axons from these receptors are myelinated! 2) Pain: response to noxious s$mulus 3) Temperature: response to cold/hot - The axons from these receptors are thinly myelinated or not myelinated! That’s why pain comes later than touch! Sensory Receptors Con$nued 4) Propiocep$on: response to posi$on or mechanical movement of muscle/joint - “Golgi Tendon Organ” For #1 and #4: Mechanical pressure bends/stretches the neural membrane, opens Na+ channels depolariza$on ACTION POTENTIAL. - These Na+ channels are STIMULUS ­gated Somatosensory Connec$ons OMATOSENS: Sensory Neurons in Skin  Spinal Cord  Brain MOTOR SYSTEM: Brain  Spinal Cord  Motor Neurons  Muscles) Spinal Cord Segment To brain From brain Dorsal Root Ganglion Dorsal Root Ganglion (DRG): Contains the cell bodies of the neurons in a sensory nerve How do Sensory Inputs Get to the Brain? 31 spinal nerves •  Dermatome: area of the skin that provides input to a single sensory nerve - 1 sensory nerve1 DRG1 spinal segment - Each dermatome overlaps 1/3 to ½ of its neighbor •  Myotome: Each muscle in the body is supplied by a par$cular segment of the spinal cord and by its corresponding spinal nerve Somatosensory Cotex Sensory Neurons in Skin  Spinal Cord  Somatosensory Cortex Sensory “Homunculus” Phantom Limbs Two requirements 1) The area of cortex that originally received input from the lost body part (e.g., the hand) is s$ll intact. 2) Ac$vity in that area s$ll “represents” that part of body. If you can ACTIVATE that area of cortex  phantom limb So, HOW can it be ac$vated? a) spontaneous ac$vity b) cut nerves from the HAND s$ll func$on, but now are s$mulated by the wrist (i.e., nerve endings are now in wrist) c) cor$cal “hand” area gets taken over by inputs from “face” (next slide) c) cor$cal “hand” area gets taken over by inputs from “face” (Ramachandran et al, UCSD) 0 0 Pain •  Invoked by harmful s$mulus: cut, chemical irrita$on, intense heat or cold Pain Reflex Arc (no brain needed!) But also to brain! 3 Levels of Pain (keep in mind for drugs that alleviate “pain”): 1)  Sensa5on of Pain: mediated by Sensory Neurons  ­ thicker axons carry sharp pain, thinner axons carry dull pain 2) Percep5on of Pain: “unpleasant” vs. “neutral” vs. “pleasant” 3) Response to Pain: distracters could mask the response Pain Pathways Sensory pathway: from sensory receptors to THALAMUS and then to SOMATOSENSORY cortex to convey sensory aspects of pain Emo5onal pathway: from sensory receptors to HYPOTHALAMUS and AMYGDALA to convey emo$onal aspects of pain Substance P •  Two neurotransmiqers (NTs) used by pain receptors (released in spinal cord and brain): –  Substance P: strong pain –  Glutamate: mild pain and strong pain Spinal Cord Neuron from skin Capsaicin (because it’s neat) •  Capsaicin: substance found in peppers that makes them hot -  Produces a burning sensa$on when you eat them by releasing substance P onto receptors on your tongue (CN 5) •  Releases substance P faster than neurons can resynthesize itneurons less able to send pain signals -  If you rub it on a sore muscle, it produces a temporary burning sensa$on followed by pain RELIEF! Body’s Own “Analgesic” Response to Pain Gate Theory (Wall, 1965): mechanism that inhibits pain …. con=nuous pain is unnecessary •  Endorphins (pep$de NTs): endogenous morphine e.g., enkephalin -  Aqach to endorphin (opiate) receptors on axon terminals of pain afferents, which inhibits or limits release of Substance P (limits “sensa$on” of pain) -  Produce similar effects to those of opiates, like morphine From brain Endorphins—also released for pleasant s$muli •  Endorphins are also released IN THE BRAIN, in response to pleasant s$muli •  Some examples: -  Sex -  Running/exercise: “Runner’s High” -  Acupuncture (euphoria) -  Listening to music •  These types of s$muli also reduce the sensa$on of pain Why Does Pain Persist? •  Imagine that you cut your leg –  Why does the pain last for a while despite endorphin ga$ng? •  Injury produces Prostaglandins (PG) and Inflamma5on -  part of healing/clorng process •  PGs and Inflamma$on increase the sensi$vity of Pain Sensory Neurons—allowing them to con$nue to respond Analgesic Drugs 2 places of drug ac$on: 1) Works “directly” at the site of injury Aspirin, Ibuprofen: An$ ­inflammatory and inhibit forma$on of PGs Tylenol (Acetaminophen): Mechanism largely unknown Topical Drugs that contain Capsaicin: Deplete Substance P 2) Works “indirectly” in the CNS Opiates: agonist for endorphin receptors e.g., Morphine, Heroine, Demerol (cross BBB) Change: (1)  “Sensa$on” (inhibit substance P release from sensory neurons in spinal cord) (2) “Percep$on” (euphoria) Opiates help for dull, but not sharp, pain! ...
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