S P Ch 13 Touch Components of Touch 1 Tactile mechanical displacement of skin a most of the section on this 2 Temperature 3 Pain including itch and tickling 4 Kinesthetic Body Sensations where body parts are Proprioception perception mediated by kinesthetic and vestibular receptors Somatosensation a collective term for sensory signals from the body also includes vestibular system 13 Sensory Organ for Touch Skin Largest sensory organ about 1 8 square meters 19 square feet About 4 kg 9 pounds Touch Receptors embedded in outer layer epidermis and underlying layer dermis of skin multiple types of touch receptions each touch receptor can be categorized by three criteria 1 Type of stimulation to which the receptor responds 2 Size of the receptive field deeper in the skin larger field 3 Rate of adaptation fast vs slow slow adapting ones will continue to fire throughout duration of pressure fast adapting ones will start firing right away but then get bored Four Types of Mechanoreceptors cells responsible for mechanically transducing pressure or vibrations into neurosensory sensations Meissner Corpuscle Merkel Cell Neurite Complex Ruffini Ending Pacinian Corpuscle HE IS GOING TO ASK YOU TO MEMORIZE THEM FOR THE EXAM named after the scientist who discovered them identify the types and their locations epidermis dermis or subcutis Merkel Cell Neurite Complex SA I slow adapting 1 1 is small receptive field located at boundary between epidermis and dermis responds best to steady downward pressure small receptive field size used to detect fine spatial detail grooves on penny sensitive to very low frequency of vibrations 5 hz slowly adapting SA 1 important for texture and pattern perception e g for Braille reading or to determine the orientation of a screw head without looking When nerve is electrically stimulated people report feeling pressure 1 Meissner Corpuscles FA 1 located at boundary between epidermis and dermis closer to the surface of the skin sensitive to low frequency vibrations between 5 hz and 50 hz fast adapting small receptive field size important to detect slip of objects across skin to correct grip around object when holding something trying to save energy and maintain hold when stimulated electrically people feel wobble or flutter Ruffini Endings SA 11 embedded deeply in the dermis responds best to sustained downward pressure and lateral skin stretch responds to finger position and grasp slowly adapting SA II large receptive field size when stimulated people experience no tactile sensation More than one SA II fiber need to be stimulated in order to be detectable Pacinian Corpuscles FA II Embedded in subcutaneous tissue respond best to high frequency vibrations of 50 700 hz active when object makes first contact with skin mosquito landing on skin hitting key on keyboard fast adapting FA II large receptive field size when electrically stimulated people report buzz Merkel when trying to find a key you find the big key based on this Ruffini this tells you finger position getting in position to hold it Meissner theyre going to make sure youre gripping the key not too hard or too slow Pacinian sliding the key into the lock feel the click of the unlock Kinesthetic Receptors play important role in sense of where limbs are what kinds of STUDY THIS movements are made Muscle Spindles convey the rate at which the muscle fibers are changing in length react to when they re elongated or not they re there if we re bending a muscle too far to stop Receptors in tendons provide signals about tension in muscles attached to tendons Receptors in joints react when joint is bent to an extreme angle Importantance of kinesthetic receptors strange case of neurological patient Ian Waterman cutaneous nerves connecting Waterman s kinesthetic mechanoreceptors to brain destroyed by viral infection Lacks kinesthetic senses dependent on vision to tell limb positions 2 Thermoreceptors Sensory receptors that signal information about changes in skin temperature Two distinct populations of thermoreceptors warmth fibers cold fibers warm detects anything warmer than body temperature cold detects anything colder than body temperature Body is constantly regulating internal temperature epidermis is a slightly lower temperature your extremities between 86 96 degrees trying to find a temperature where our cold fibers are as active as a warm fibers Thermoreceptors respond when you make contact with an object warmer or colder than your skin Nociceptors Sensory receptors that transmit information about noxious painful stimulation that causes damage or potential damage to the skin Two groups of nociceptors A Delta Fibers fast transmission to brain respond to strong pressure crushing and heat initial and quick sharp burst of pain at injury time C Fibers slower response sustained stimulation throbbing sensation that evolves after initial surge of pain Benefit of Pain Perception sensing dangerous objects hot pots in the kitchen Case of Miss C born with insensitivity to pain could not protect herself did not sneeze or cough died at age 29 from untreated infection Huge problem for diabetic patients who often lose sensation of their feet and become invalids because of untreated minor injuries Responses to noxious stimuli can be moderated by anticipation religious belief prior experience watching others respond and excitement Ex wounded soldier in battle who doesn t feel pain after Analgesia Decreasing pain sensation during conscious experience Soldier in ex experienced effect because of endogenous opiates chemical released in body to block release or uptake of neurotransmitters transmitting pain sensation to brain Endogenous opiates may be responsible for certain placebo effect Externally produced substance have similar effect morphine heroin codeine Gate Control Theory the brain A description of the system that transmits pain that incorporates modulating signals from Feedback circuit located in dorsal horn of spinal cord Gate neurons that block pain transmission can be activated by extreme pressure cold or other noxious stimulation applied to another site distant from the source of pain Touch sensations travel as far as 2 meters to get from skin and muscles of feet to brain Information must pass through spinal cord First Synapse Axons of various tactile receptors combine into single nerve trunks 3 Several nerve trunks from different areas of body Pathways from skin to cortex Once in spinal cord two major pathways Spinothalamic