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Lecture 8

lecture 8

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University of Toronto St. George
Doug Mac Kay

08 Somatosensory ReceptorsSeptember 26 2007Somatosensory receptorstypemechanoreceptoroa cutaneous receptorsdetect skin pressure and stressfound in skinob proprioceptorsdetect forces in muscles and jointsfound in deep tissue muscles and joint capsules or tendonsjoints are filled with fluid and encapsulated Cutaneous receptorsSensory axons classified by size and conduction velocityoAlarge diameter myelinatedonly mechanoreceptors 50 msoAsmall diameter myelinatedmechano thermo and nociceptors 10 msoCsmall diameter unmyelinated 1 msslow conductingsensory endings are in the upper and lower parts of the dermal layersosensory endings are associated with external cells that form a capsules corpuscle Pacinian corpuscleLargest cutaneous receptorlocated deep in dermal layers hands feet lipsrapidlyadaptingresponds best to skin vibration at 200 Hz maximum responseoresponds to changes of pressurevery sensitive to touch threshold about 05 mmonly need slight touch to generate action potentialohuge receptive fieldMeissnersmall and shallow receptive fieldrapidly adaptingMerkel diskSlowly adaptingresponds to maintained pressure on the skinSmall receptive fieldthreshold response to skin indentations of 20 micronsostimulation of axon gives sensation of leaf pressing against receptive fieldProprioceptorsgives sense of body position and where everything is relative to the bodyMuscle spindleadequate stimulus is passive stretch group Ia afferentsoFound right in the belly of the muscle tissue and activated by stretchingGolgi tendon organadequate stimulus is active force group Ib afferentsoFound in junctions of muscle tissue or tendon and activated by contractionsjoint receptorsdetect orthogonal paciniformleaning on the joint or tangential Ruffini receptorsbending the joint force in joint capsule group IIProprioceptor Classification1
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