2. CUTANEOUS SENSES Overview of Cutaneous Senses Receptors and Fibers Pathways Gate Control Theory Phantom Limbs

3. Overview of Cutaneous Senses Touch Temperature Pain

4. Rapidly Adapting Receptors respond to changes in skin stimulation Meissner corpuscle (RA1) - responds to flutter; small receptive field Pacinian corpuscle (RA2) - responds to vibration; large receptive field

5. Slowly Adapting Receptors respond to constant skin stimulation Merkel disk (SA1) - responds to pressure; small receptive field Ruffini cylinder (SA2) - responds to stretching; large receptive field

6. Thermoreceptors Different thermoreceptors for warm and cold temperatures Warm and cold spots

7. Thermoreceptors paradoxical cold: sensation of cold when a warm stimulus touches a cold spot thermal adaptation: intensity of hot or cold stimulus decreases over time

8. Medial Lemniscal Pathway touch, proprioception, kinesthesis large, fast fibers

9. Medial Lemniscal Pathway fibers cross to opposite side of brain brain stem thalamus: Ventral Posterior Nucleus (VPN) somatosensory receiving area (S1) secondary somatosensory cortex (S2)

10. Spinothalamic Pathway temperature, pain thin fibers, slow transmission

11. Spinothalamic Pathway fibers cross to opposite side of brain limbic system (emotion, memory) thalamus (VPN) somatosensory receiving area (S1) secondary somatosensory cortex (S2)

12. Somatosensory Cortex Homunculus Cortical Magnification Columns of cells with the same receptive field

13. Gate Control Theory Nociceptors in the skin send pain signals to the brain Why is the pain not always experienced?

14. Gate Control Theory Cells in the Substantia Gelatinosa (SG) in the spinal cord serve as a gate, determining whether the Transmission cells (T-cells) send the signal to the brain – SG+ cells send the signal – SG- cells stop the signal

15. Gate Control Theory Large (Medial Lemniscal) fibers stimulate SG- cells, closing the gate Small (Spinothalamic) fibers stimulate SG+ cells, opening the gate The brain can also stimulate SG- cells to close the gate

16. SG- SG+ Transmission Cell Brain Large Fiber Small Fiber

17. Phantom Limb Pain Pain felt in amputated limb Produced by the brain Reorganization of cortex after loss of limb

18. Factors Affecting Pain Perception pain adaptation: a painful stimulus becomes less painful over time (for mild pain only) expectation attention