Psyc 362 Chapter 7 text Audition the body senses and the chemical senses Somatosenses Function Provides information about what s happening on the surface and inside of our body Cutaneous skin senses include touch submodalities Proprioception provides info about body position and posture Kinesthesia provides information about the body s own movements Organic senses arise from receptors in and around the internal organs The Stimuli Cutaneous senses respond to the following Pressure mechanical deformation of the skin Vibration produced by tuning forks or mechanical devices in lab commonly occurs when we move our fingers across a rough surface vibration sensitivity used to judge an object s roughness heating and cooling Warmth and coolness produced by objects that raise or lower skin temperature from normal Pain different stimuli that most often cause at least some tissue damage Kinesthesia causes one source is the stretch receptors found in skeletal muscles which change report changes in length to CNS when receptors in joints respond to the magnitude and direction of limb movement most important source comes from receptors that respond to changes in the stretching of the skin during movements of the joints and muscles Anatomy of the Skin and its receptive organs The skin thermoregulates with sweat to cool and restriction of blood circulation to heat Its appearance varies throughout the body from mucous membranes to hairy skin to glabrous skin the smooth hairless skin of the palms and soles of the feet Skin consists of subcutaneous tissue dermis and epidermis and contains various receptors glabrous skin contains a dense complex mixture of receptors reflecting how we actively use our hands and fingers to explore the environment the rest of the body contacts the environment passively that is with other things coming into contact with it four types of encapsulated receptors Merkel s disks small touch sensitive end organs found at the base of the epidermis adjacent to sweat ducts They detect form and roughness especially by fingertips Ruffini corpuscles large vibration sensitive organ located in hairy skin which detects static force against skin skin stretching and proprioception Meissner s corpuscles small touch sensitive end organs located in the papillae small elevations of the dermis that project up into the epidermis they are only in glabrous skin and detect edge contours braille like stimuli especially by fingertips pacinian corpuscles large specialized sensory nerve ending that detects mechanical stimuli especially vibrations Perception of Cutaneous Stimulation Touch involves sensitivity to pressure and vibration as caused by movement of the skin which moves the dendrites of mechanoreceptors such dendritic movement appears to cause ion channels to open and the flow of ions into or out of the dendrite causes a change in the membrane potential we can perceive the location on our skin where we are being touched smalldiameter unmyelinated axons appear responsible for temperature pain and itch Its associated with the insular cortex which responds to emotions and sensations from internal organs Large myelinated cells responsible for touch Temperature have two categories of receptors those that respond to warmth and those that respond to coolness Cold sensors in skin are just beneath the epidermis Information is conveyed to the CNS by thinly myelinated A fibers Warmth receptors are more deeply in the skin Information is conveyed by unmyelinated C fibers We detect thermal stimuli over a very wide range of temperatures less than 8 degrees C which is noxious cold to over 52 degrees C which is noxious heat We know of 6 mammalian thermoreceptors Some respond to particular chemicals as well as changes in temp EX TRPM8 in leaves of mint Pain reception is accomplished by networks of free nerve endings in the skin like thermoreception There are 3 types of receptors nociceptors High threshold mechanoreceptors are free nerve endings that respond to intense pressure Free nerve endings that respond to extremes of heat to acids and to the presence of capsaicin the active ingredient in chili peppers Contains TRP V1 receptors most likely responsible for pain produced by burning of the skin and to changes in the acid base balance within the skin Also appear to play a role in regulation of body temp another nociceptive fiber contains TRPA1 receptors that are sensitive to pungent irritants found in mustard oil wintergreen oil horseradish garlic and a variety of environmental irritants like those found in vehicle exhaust and tear gas Primary function is providing info about the presence of chemicals that produce inflammation The Somatosensory Pathways Somatosensory axons from the skin muscles or internal organs enter CNS via spinal nerves while those in the face head enter through the trigeminal cranial nerve cell bodies of the unipolar neurons in the dorsal root ganglia and cranial nerve ganglia Axons conveying precisely localized info ascend through the dorsal columns in the spinal cord to the lower medulla where those axons cross the brain and ascend through the medial lemniscus to the ventral posterior nuclei of the thalamus the relay nuclei for somatosensation From the thalamus axons project to the primary somatosensory cortex and from there to the secondary somatosensory cortex Those that convey poorly localized info form synapses with other neurons as soon as they enter the spinal cord then cross to the other side of the cord and ascend through the spinothalamic tract to the ventral posterior nuclei of the thalamus Damage to the somatosensory association cortex can cause tactile agnosia inability to recognize objects by touch which requires cooperation between the somatosensory and motor systems Case study with damage to the right hemisphere causing tactile apraxia difficulty in carrying out purposeful finger movements in the absence of paralysis or muscular weakness Perception of Pain Can only be defined by some sort of withdrawal reaction or verbal report Can be modified by opiates hypnosis and administration of pharmacologically inert sugar pills by emotions and even by other forms of stimulation 3 different perceptual and behavioral effects involving different parts of the brain 1 the sensory component pure perception of the intensity of a painful stimulus mediated by a pathway from the spinal cord to the ventral posterolateral thalamus to the primary and secondary somatosensory cortex 2