Slide 1Somatosensory SystemLabeled Line SystemLabeled Line SystemReceptor PotentialAdaptationReceptive FieldsSize of Receptive FieldsThe Spinal CordSomatosensory PathwaysRelating the Somatosensory and Motor SystemsDermatomesSomatosensory PathwaysThalamusThalamus to CortexSomatosensory CortexSomatotopic MapModulation of Somatosensory RepresentationTwo Types of Pain ReceptorsPeripheral Mediation of PainAscending Pain PathwaysAscending Pain PathwaysDescending Pain PathwaysReferred PainModulation of PainOpiatesOpiate Receptors in the Rat BrainTouch and PainJanuary 29, 2016Somatosensory System•Relays information about the body–Touch–Temperature–Body position = proprioception–Organic senses (heart burn)–Pain = nociceptionLabeled Line System•Receptors = neurons that transduce or change a physical stimulus into neural events.•In the skin, each receptors has a specialized ending that responds to a specific attribute of the stimulus.• Labeled line = different receptors for different qualities and have different lines to the brain.Labeled Line SystemReceptor Potential•A Pacinian corpuscle responds to pressure–When deformed (skin pressed), sodium channels are opened, which depolarizes the ending.–Receptor or generator potential is the potential measured in the specialized ending. If ending depolarized enough, produce an action potential.Adaptation•Adaptation = loss of sensitivity to continuous presence of stimulus.Receptive FieldsEach receptor has a receptive field = the region of the receptor surface that excites or inhibits a sensory neuron.Size of Receptive Fields•For each type of receptor, the receptive fields are smallest in the fingertips, larger in the hand, even larger in the arm.•Receptive field size varies with use.The Spinal CordSomatosensory Pathways• Cell body in dorsal root ganglion• Information ascends in the dorsal columns to the medulla, then to thalamus and then to somatosensory cortexSomatosensory CortexRelating the Somatosensory and Motor Systems•Spinal Segments and Dermatomes–Each spinal segment corresponds to a region of body surface called a dermatome.DermatomesSomatosensory PathwaysThalamusThalamus to CortexSomatosensory Cortex•Somatosensory cortex is just posterior to the central sulcusAnterior PosteriorVentralDorsalSomatotopic MapModulation of Somatosensory RepresentationTwo Types of Pain Receptors1. Thermal or mechanical receptors •Sharp, prickling pain•Axons (A – fibers) are myelinated2. Polymodal receptors •Searing, diffuse pain•Axons (C – fibers) are unmyelinatedPeripheral Mediation of PainAscending Pain Pathways•Pain fibers synapse in the dorsal horn•Spinothalamic tract carries the pain fibers to the thalamus.Ascending Pain Pathways•Left–Spinothalamic tract (blue) carries the pain fibers to the thalamus.–Spinoparabrachial pathway (red) innervates areas of the brain concerned with affect•Right–Descending pathway begins in periaqueductal gray (PAG)Descending Pain PathwaysMidbrain (periaqueductal gray)Medulla (Raphe nucleus)Spino-thalamic tractDorsal horn neuronPain fiberIPSPEPSPEPSPReferred Pain•Pain fiber from skin or muscle and pain fiber from an internal organ (e.g. heart) synapse on the same dorsal horn neuron•Pain in internal organ feels like pain in muscle or skinSpino-thalamic tractDorsal horn neuronEPSPsFrom skin or muscleFrom internal organModulation of Pain•Analgesic–Blocks the sensation of pain but does not produce unconsciousness•Anesthetic –Analgesia plus unconsciousness•Placebo–Phony drug that appears to alleviate pain (~30% of the time)•Endorphins–Endogenous drugs that produce pain relief by activating the descending pathwayOpiates•Known to have medicinal properties (1500 B.C.)–Reduce pain without unconsciousness, but with relaxation and sleep–Produce a sense of well-being and euphoria–Reduces coughing–Relief from diarrhea and dysentery•Used in tonics, syrups, and wines–Laudanum wine (“something to be praised”)•Morphine–Common analgesic–Derived from opiumOpiate Receptors in the Rat BrainRed shows the highest concentration, followed by orange, yellow,