Somatosensory Systems cutaneous proprioceptive Adequate Stimuli Thermal (infrared radiation, contact) Touch (light touch, pressure, vibration) Pain and Itch (chemical, thermal, mechanical) Proprioception (mechanical; stretch or pressure) epicritic location vibration texture shape protopathic pain temperature itch and tickle Cutaneous subsystems Epricritic, or non-pain Somatosensation MeissnersMerkels Pacinian Riffinis Free nerve ending 60 hz vibration Stretch 200 hz vibration Pressure Pain As in the retina, receptive fields vary in size. Smaller receptive fields = greater acuity two-point discrimination Center-surround organization of cutaneous receptive fields results in lateral inhibition, as in retina Serves to enhance contrast Protopathic, or pain Somatosensation Free nerve endings that respond to: mechanical stimuli thermal stimuli chemical stimuli, or all three (polymodal receptors) Pain Receptors Called Nociceptors Free nerve endings of unmyelinated C fibers or thinly myelinated A fibers Cutaneous classified by conduction velocity Proprioceptive classified by axon diameter SubstanceEffect Potassiumactivation Bradykininactivation Histamineactivation Prostaglandinssensitization Substance Psensitization Gate control theory of pain control Referred Pain CN V and VII Parallel Processing in the Somatosensory System Lemniscal System (non-pain; epicritic) Extralemniscal System (pain; protopathic) Spinothalamic pathways Neospinothalamic Paleospinothalamic Spinomesencephalic Neospinothalamic PaleospinothalamicSpinomesencephalic Neospinothalamic Pathway Paleospinothalamic Pathway Spinomesencephalic Pathway Descending control of pain Sensory System Summary 1. Sensory systems detect change over space (lateral inhibition to enhance contrast) over time (rapidly adapting) 2. Detect features 4. Parallel pathways 5. Hierarchical processing 6. Topographical organization 7. Non-uniform receptive fields 8. Extreme sensitivity, wide dynamic range 9. Non-linear response 3. Structures are laminated (cells in layers)