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Chapter 12

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Matthias Niemeier

Chapter 12Somatic Sensory System IntroductionSomatic sensation Enables body to feel ache chill and know what parts are doingSensitive to many kinds of stimuli Pressure of objects on skin position of joints and muscles distension of bladder temperature of limbs and brainSomatic sensory system is different from other sensory systems 1 Receptors distributed everywhere on bodytouch temperature pain and body position 2 Is catchall namecollective category for all sensations that arent the 5 sensesTouchBegins at skinmajor skin types are hairy and glabroushairlessOuter layerepidermis and inner layerdermisFinger can feel raised dot of 0006 mm high 004 mm wide braille dots 167X higher Mechanoreceptors Of The SkinMost sensory receptors are mechanoreceptorssensitive to physical distortion ie bending and stretchingAxons have mechanosensitive ion channelstheir gating depends on stretching or changes in tensionBest studies and largest receptor is Pacinian corpuscleDeep in dermislargest of 2mm and 1 mm in diameter 0 200300 Hz hand on vibrating speakers Ruffinis endingin hairy and glaborous skinare smaller than Pacinian corpuscles super low frequencies yields fluttering feelingMessiners corpuscles are 110 size of Pacinians at ridges of glaboroushairless skin 50 Hz finger hitting bumps of speaker ie raised part offingertipsense textureMerkels disks consist of nerve terminal and flattened nonneural epithelial cellmay be the mechanically sensitive partsynapselike junction with nerve terminalKrause end bulbs Lie in border regions of dry skin and mucous membrane ie lips and genitalsSkin can be vibrated pressed pricked stroke d and hair can be bent and pulledMessiner and Merkel have small receptive fieldPacinian and Ruffinis have large receptive field from fingertip of palmMessners and Pacinianrespond quickly then stop firingrapidly adaptingMerkels and Ruffinisslowly adaptinggenerate sustained response during long stimulus
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