SA Medical - General Medicine And Imaging of Disease

Pain Sensation: fast and Slow Pain Classification Fast Pain Slow Pain All pain receptors are free nerve endings Three types of Stimuli Pain receptors are activated by mechanical, thermal and chemical stimuli Mechanical and thermal stimuli - fast pain Chemical stimuli - slow pain No adaptation, progressively greater as the pain stimulus  continues, this is called hyperalgesia Two separate pathways of Pain transmission A-delta fibers fast - 6 to 30m/s - Mechanical and thermal stimuli C-Fibers slow - 0.5 to 2m/s  neospinothalamic tract - A-delta fibers paleospinothalamic tract - C-fibers The neospinothalamic tract is used in pain localisation Activity in the paleospinothalamic system may impart unpleasant perception of pain. paleospinothalamic pathway Brain and Spinal Cord: Internal Pain Suppression system The periaqueductal gray  the periadueductal gray of the midbrain and the rostral pons receives input from the ascending pain pathways in addition to descending proje

General Organisation; the tactile and Position senses The somatic senses can be divided into three main components Mechanoreceptors  Thermoreceptors Nociception - pain and damage discriminative - precisely localised touch  Crude - poorly localised - proprioception - touch, pressure, vibration and the senses of static body position and movement Exterioceptive sensation  Visceral sensations Detection and Transmission of Tactile Sensation Even though touch, pressure and vibration are often classified as separate and distinct sensations, they are each detected by the same general class of tactile receptors: the Mechanoreceptors Free nerve endings - skin and in the cornea of the eye Meissner's corpuscule -    The   tactile corpuscles of Wagner and Meissner   (Fig. 936)   are oval-shaped bodies.   These tactile corpuscles occur in the papillæ of the corium of the hand and foot, the front of the forearm, the skin of the lips, the mucous membrane of the tip of the t