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Lecture 11

PSYB51 lecture 11.docx

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Matthias Neimier

PSYB51- Lecture 11 – Touch What are formants? What are they good for? Touch and more... • Touch: Mechanical displacements and other physical 
 impacts on the skin. • Proprioception: Perception mediated by kinesthetic and vestibular receptors. • Somatosensation: A collective term for sensory signals from the body • Actions play a special role: haptics Somatosensory Physiology – Receptors – Pathways to the brain – How we perceive pain. Volunteers for demo? • Hold a pen. What do you feel? • => subtracting (less interesting) sensation of the pen Volunteers? • 2 separate locations stimulated multiple times in quick succession feels like a rabbit, hopping across the skin between the 2 locations Investigated with fMRI • Middle location equally activated as stimulated locations Touch receptors: Embedded in outer layer (epidermis) and underlying layer (dermis) – Multiple types of touch receptors – Touch receptors (& other somatosensory 
 receptors) have three attributes:
 1. Type of stimulation the receptor responds to 2. Size of the receptive field
 3. Rate of adaptation Tactile receptors (four): Mechanoreceptors- respond to mechanical stimulation or pressure – Meissner corpuscles (epidermis) – Merkel cell neurite complexes (epidermis)
 – Pacinian corpuscles (dermus, deeper down, less sensitive to smaller spaces on skin) – Ruffini endings * Know these 4 for final exam  FAI (fast adaptation): skin slip; low-frequency vibration (3-40Hz)
  FAII: first contact with objects: high frequency vibration (50-700 Hz)  SAI (slow adapting): small receptive fields, fine spatial details, can sense textures, patterns, persons who read Braille are trained to use them in an efficient way; sustained pressure, spatial deformations (<5 Hz)  SAII: lateral stretch(e.g., grasping), hand shape; low sensitivity to vibration (have large receptive fields)  Other types of mechanoreceptors within muscles, tendons, and joints:  Proprioceptive/kinesthetic receptors: Necessary to sense – Tells us where limbs are / posture
 – what kinds of movements are made – they signal stretching of muscles (ex. I‟m extending my elbow)  Spindles: Convey the rate at which the muscle fibers are changing in length  Receptors in tendons provide signals about tension in muscles attached to tendons > if you work out too much and then flex your muslces, it‟s possible that you could hurt your tendons  Receptors in joints react when joint is bent to an extreme angle  Proprioceptive illusion I: get a blindfolded person to hold chopsticks an touch and object and guess what is it (in this case, it was a Rubic‟s cube)  Proprioceptive illusion II: tapping the ends of an arm and the person is supposed to feel that there‟s some tapping all over her arm (like a rabbit hopping)  Proprioceptive illusion III (when person A tries to forcefully open person B‟s crossed arms and then lets go to relax, person A‟s arms are automatically in a stiff position) • Demo = 2 volunteers  Thermoreceptors:
 – Sensory receptors that signal information about changes in skin temperature
 – Warmth fibers, cold fibers
 – Body is consistently regulating internal temperature – Thermoreceptors kick into gear when you make contact with object warmer or colder than your skin  Nociceptors: – Sensory receptors that transmit information about noxious stimulation that causes damage or potential damage to the skin – A-delta fibers: strong pressure, heat; myelinated  fast (basically, the greater the diameter of the axon, the faster the transmission) – C fibers: pressure, heat, cold, chemicals; unmyelinated  slow – 2 phases of pain: When you hurt yourself, you experience two phases of pain; first is some sort of quick sharp perception, and second is some sort of slower pain that comes later Benefit of pain perception:
 – Sensing dangerous objects – Hansen‟s disease (Leper‟s disease): reduced ability to perceive pain-> you might cause damage to your body because you can‟t feel the pain so you don‟t know that you‟re hurting your body  Pathways: up to 2 meters long - Information must pass through spinal cord - Axons of various tactile receptors combine into single nerve trunks - Several nerve trunks from different areas of body - Once in spinal cord, 2 major pathways: Spinothalamic (slower); dorsal (in the neck; at the back) column- medial lemniscal (faster)-> KNOW THIS FOR FINAL EXAM  Spinothalamic pathway synapses multiple times within spinal cord: slow, nociception, thermal information – Why is pain slow? (ex. why don‟t we burn our hands when we put it on a hot plate?) Shouldn‟t it be fast?-> we have reflexes (operate at the level of the spinal cord-> from one sensory neuron directly to a motor neuron)  Dorsal-column-medial- lemniscal (DCML) pathway: Fast  Synapse in medulla, near base of brain, then ventral posterior nucleus of thalamus, then somatosensory area 1 (S1), somatosensory area 2 (S2)-> this is secondary  Patient with selective lesion in DCML pathway felt passive hand movements over surface – why?? - as you move your arms around the air, you feel the resistance of the air and you feel that it‟s cool, but it‟s actually processesity to the point that it‟s going in another pathway  Touch sensations are represented somatotopically: Analogous to retinotopy found in vision (look at the diagram of the brain) – Adjacent areas on skin: Connected to adjacent areas in brain, called homunculus The following image is a representation of the amount of neurons used and affected by S1 – Distorted representation reflects receptor density. – Brain contains several sensory maps of body, several homunculi, i.e., different subareas of S1, secondary areas as well – The lips take up a lot of space, while there are very few neurons that response to the touch on the shoulder ; many neurons are sensitive to the touch of the hands  Phantom limb: – Perceived sensation from a physically amputated limb of the body – Parts of brain listening to missing limbs not fully “aware” of altered connections, so they attribute activity in these areas to stimulation from missing limb (ex. someone could feel that someone is touching his hand if we touch them on their upper arm) – Phantom pain : if you have a cramp in your hand, you‟d open up your hand to relax it, but if you don‟t have the hand, you can‟t do that ; extremely uncomfortable because you can‟t do anything about it  Pain: – Pain sensations triggered by nociceptors – Responses to noxious stimuli can be moderated by cognitive, emotional and social factors – Bottom-up sensation + top-down modulation – Example: Injury during sports (bottom-up mechanism)-> some activities change your body in a way that they reduce your ability to perceive pain (endorphins. Morphine-> artificial way) ; the body creates it‟s own drugs and you may get addicted to it, ex. running  Analgesia:
 – Decreasing pain sensation during conscious experience – Sports injury: endogenous opiates released in body to block transmission of pain sensations  Gate control theory (bottom-up mechanism): Describes a pain transmitting system that incorporates modulating signals from the brain – Fe
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