Brain and Behavior Exam 3 Touch and Pain Senses are found in the somatosensory cortex Somatosensation touch receptors in CNS shape object men o Touch receptors can be simple bare neuron endings barely myelinated to feel warm cold pain or encapsulated receptors modified dendrites Merkel disks elaborated neuron endings to feel touch o Touch receptors are mechanoreceptors activated by force stimulation stretch displacement of skin o Activation opens sodium channels and triggers an action potential afferent goes towards the spinal cord The sensory neuron cell body is located in DRG o Shallow layers of receptors Meissner s corpuscle Merkel disks for fine detail movement stroke for o Deep layers of receptors Pacinian corpuscle Ruffini endings for stretch perception of shape of grasped Receptive field group of sensory neurons each w different sensitivity to touch that converge overlap on spinal cord o The more closely packed the receptive fields the more sensitive it is to touch stimuli Merkel disks shallow layer receptors that respond to light touch stroke equal amount in men and women o Women tend to have smaller fingers so more compacted disks making them more sensitive to touch than Information from touch receptors in the head enters the CNS through cranial nerves Information from receptors below the head enters spinal cord and travels through 31 spinal nerves to the brain o Each spinal nerve has a sensory and motor component and connects to a limited area of body o Dermatomes overlapping skin areas connected to or innervated by a single sensory spinal cord o Sensory info entering spinal cord travels in well defined distinct pathways ex touch or pain pathway Somatosensory cortex o Various areas of somatosensory thalamus send impulses to different areas of somatosensory cortex in parietal lobe many body sensations remain separate all the way until cortex o Different subareas of the cortex respond to different areas of the body o Damage to cortex can result in impairment of body perceptions The homunculus areas of greatest innervation in humans corresponds to rat whisker barrels cortical field around whisker Pain sensation begins with bare nerve endings least specialized of all receptors it is an experience evoked by a harmful stimulus directs our attention and holds it o Capsaicin found in hot pepper stimulates some pain receptors that respond to acids heat or cold o Axon impulses carrying pain are slow little no myelination but motor responses are fast brain processes o Mild pain triggers release of glutamate in spinal cord stronger pain triggers release of glutamate and quickly substance P Pain receptors Substance P results in increased sensitivity to pain o Can be mechanical pinch cut thermal hot cold or polymodal all mechanical thermal plus a chemical your body releases when tissue is injured pain is pure perception stimulus is tissue damage o Nociceptors respond to pain and release chemical stimuli basis of inflammation o Descending brainstem fibers are excitatory opiate neurons are inhibitory morphine external opioid Pain pain tickle temperature vs touch recognition of shape size texture o Each one follows its own pathway to brain o From medulla to cerebral cortex touch pain represented on contralateral side o On spinal cord touch travels on ipsilateral side and pain on contralateral Pain sensitive cells in spinal cord relay information to o Somatosensory cortex for painful stimuli memories of pain and signals that warn of impending pain o Emotional associated parts central nuclei of thalamus amygdala hippocampus prefrontal cortex cingulate cortex Pain control the midbrain body o Activating opioid receptors blocks release of substance P in spinal cord periaqueductal gray area in o Capsaicin dumps substance P so have to remake opioid mechanisms or can damage pain receptor o Cannabinoids chemicals related to marijuana that block certain types of pain mainly in periphery of Gate theory touch or emotional information like happiness sends message to spinal cord at the same time as pain receptors and therefore close the gate and decrease pain perception o Pain signals ascend the pain pathway and reach conscious awareness in the thalamus and cortex o Descending pathways can close the gate and keep the CNS from receiving pain signals o CNS activates neurons that release endorphins to block release of substance P keeping pain signals from getting in o Decrease pain perception by decreasing brains emotional response in cingulate cortex not Placebo drug procedure with no pharmacological effect Mechanisms in body that increase pain sensitivity somatosensory receptors o Damaged inflamed tissue release histamine nerve growth factor that increase response of nearby pain o Non steroidal anti inflammatory drugs ibuprofen decrease chemicals that pester pain receptors Chronic pain receptors become potentiated after intense barrage of painful stimuli Emotional pain resembles physical pain increased activity in cingulate gyrus when person feels emotionally hurt o Activates distinct pathway in spinal cord to brain that travels very slowly pain itch have inhibitory Itch like an anti pain caused by release of histamines relationship o Opiates increase itch and decrease pain Temperature and thirst Body and behavioral regulation of temperature exists Ticking poorly understood laughing is not normal laughter doesn t predict subsequent laughter o Temperature regulation is one of body s biological priorities 2 3 of energy a day o Basal metabolism energy used to maintain constant body temperature while at rest o Temperature affects behavior vital to normal functioning of many behavioral processes Homeostasis temperature regulation biological processes that keep certain body variables within fixed range Set point single value that body works to maintain water glucose level calcium fat acid in body o Negative feedback processes that reduce discrepancies from the set point o Allostasis opposite of homeostasis way that body changes its set point in response to life environment changes environment Poikilothermic cold blooded amphibians reptiles most fish body temperature that matches that of its o Organism lacks the internal physiological mechanisms of temperature regulation o Temperature regulation is accomplished by choosing locations in the environment Homeothermic warm blooded mammals birds internal physiological mechanisms maintain constant body temperature o Requires energy and fuel o Decrease
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