Somatosensation

I.          Types of Stimuli and Receptors

            A.         Stimuli for Cutaneous Receptors

                        1.            Touch

                        2.            Deep pressure

                        3.            Cold

                        4.            Warmth

                        5.            Tissue damage (results in pain perception)

            B.         Receptors for touch

                        1.            Free nerve endings

                        2.            Hair follicle receptors

                        3.            Meissner's corpuscles

                        4.            Pacinian corpuscles

                        5.            Merkel's disks

                        6.            Ruffini endings

                        7.            Kraus end bulbs

                        8.            itch & tickle receptors?

            C.         Types of Skin

                        1.            Hairy

                        2.            Glabrous (non-hairy)

                        3.            Mucocutaneous zones

II.         General pathway

            A.         End organ

            B.         Spinal cord

            C.         Thalamus

            D.         Somatosensory cortex and beyond

III.        Specific Pathways

            A.         Dorsal Column-Medial Lemniscus

                        1.       Information carried

                                  a.       touch (light pressure)

                                  b.       proprioception

                                  c.       2-point discrimination

                                  d.       vibration

                        2.       Pathway

                                  a.       end organ to dorsal cord, ascends in dorsal columns

                                  b.       decussates in medial lemniscus, passes to thalamus

                                  c.       thalamus to S1

            B.         Spinothalamic

                        1.       information carried

                                  a.       pain (tissue damage)

                                  b.       temperature

                        2.       Pathway

                                  a.       end organ to dorsal cord, decussates

                                  b.       ascends to thalamus via contralateral white matter

                                  c.       thalamus to S1and beyond