Brain and Behavior Exam 3 Touch and Pain Senses are found in the somatosensory cortex Somatosensation touch receptors o Touch receptors can be simple bare neuron endings feel warm cold pain or encapsulated receptors touch Merkel disks elaborated neuron endings o Touch receptors are mechanoreceptors activated by force stimulation stretch displacement of skin o Activation opens sodium channels and triggers an action potential to the spinal cord The sensory neuron cell body is located in DRG and is afferent goes toward CNS o Shallow layers of receptors Meissners corpuscle Merkel disks for fine detail movement stroke for shape o Deep layers of receptors Pacinian corpuscle Ruffini endings for stretch perception of shape of grasped object cord men Receptive field group of sensory neurons each w different sensitivity to touch that converge overlap on spinal o The more closely packed the receptive fields the more sensitive to touch stimuli Merkel disks receptors that respond to light touch stroke equal in men and women o Women tend to have smaller fingers 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 travel 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 evoked by 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 to no myelination motor responses are fast brain processes quickly substance P o Mild pain triggers release of glutamate in spinal cord stronger pain triggers release of glutamate and Pain receptors can be mechanical pinch cut thermal hot cold or polymodal both plus 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 Pain pain tickle temperature vs touch recognition of shape size texture o From medulla to cerebral cortex touch pain represented on contralateral side o Spinal cord touch travels on ipsilateral side and pain on contralateral Pain sensitive cells in spinal cord relay information to somatosensory cortex for painful stimuli memories of pain and signal of impending pain or to central nuclei of thalamus amygdala for emotional association Pain control o Opioid mechanisms like opioid drugs chemicals activate opiate receptors which blocks release of substance P in spinal cord and periaqueductal gray area of midbrain o Capsaicin dumps substance P so have to remake it or can damage pain receptor o Cannabinoids chemicals related to marijuana that block certain types of pain mainly in periphery Gate theory touch receptors axons descending from brain send message to spinal cord at same time as pain receptors and therefore close the gate decrease pain perception o Pain signals ascend the pain pathway and reach conscious awareness in the thalamus and cortex o CNS activates neurons that block release of substance P keeping pain signals from getting in Placebo drug procedure with no pharmacological effect o Decrease pain perception by decreasing brains emotional response in cingulate cortex not 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 felt left out people that take Tylenol report less hurt feelings Itch not a pain release of histamine activates distinct pathway in spinal cord to brain that travels very slowly Pain and itch have inhibitory relationship opiates increase itch while antihistamines decrease itch Ticking poorly understood laughing is not normal laughter doesn t predict subsequent laughter Temperature and thirst Homeostasis temperature regulation biological processes that keep certain body variables within fixed range o Temp regulation uses about 2 3 of energy one of body s biological priorities o Basal metabolism energy used to maintain a constant body temperature while at rest o Temperature affects behavior vital to normal functioning of many behavioral processes 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 adaptive way in which body changes its set point in response to changes in life or environment Poikilothermic body temperature that matches that of its environment amphibians reptiles and most fish o Organism lacks the internal physiological mechanisms of temperature regulation o Temperature regulation is accomplished by choosing locations in the environment Warm blooded internal physiological mechanisms to maintain constant body temperature mammals and birds o Requires energy and fuel o Decrease temperature by sweating or panting o Increase temperature by shivering increasing metabolic rate decreasing blood flow to skin Reasons for maintaining a constant temperature of around 37 degrees C 98 degrees F o Muscle activity is always ready for vigorous activity in warmer temperatures o Proteins do not function properly in higher temperatures o Reproductive cells require cooler temperatures Fever body s defense against illness bacterial viral infections too high of a fever can be harmful or lethal o How
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