Thursday March 27 y Brain Behavior Touch and Pain fields Touch Touch receptors Distortion due to variation in the size and density of sensory neuron receptive simple bare neuron ending warm cold pain encapsulated receptors touch modified dendrites elaborated neuron ending stimulation opens sodium channels to trigger an action potential Sensors mechanoreceptors they are activated by physical force stretching displacement of the skin opens channels to activate them when activated send APs up axon toward spinal cord sensory neuron cell body is located in DRG afferent fibers go toward CNS Shallow layers meissner s corpuscle and merkel disks fine detail movement Deep layers 1 Pacinian corpuscle and ruffini endings strech perception of the shape of a grasped object Thursday March 27 y receptive field group of sensory neurons that converge on the same neuron in the Receptive Fields spinal cord form receptive fields overlap to some extent women have better detailed touch than men merkel disks receptors that respond to light touch i e gentle stroking of the skin Touch receptors to brain spinal nerves to the brain limited area of the body info from touch receptors in head enters CNS through cranial nerves info from receptors below the head enters the spinal cord and travel through the 31 each spinal nerve has sensory component and a motor component connects to a dermatome skin are connected to or innervated by a single sensory spinal nerve they overlap sensory info entering spinal cord travel in well defined distinct pathways Example touch pathway is distinct from pain pathway various areas of the somatosensory thalamus send impulses to different of the somatosensory cortex located in the partial lobe damage of somatosensory cortex can result in impairment of the body perceptions whisker barrels large field cortical representation found in whiskers of rats Pain experience evoked by a harmful stimulus directs our attention and holds it Pain 2 capsaicin chemical found in hot pepper stimulates these receptors axons carrying pain info have little or NO myelin impulses travel slowly Brain processes pain info rapidly and motor responses are fast Thursday March 27 y mild pain triggers glutamate in spinal cord stronger pain triggers releases glutamate and substance p substance p results in the increased intensity of pain PAIN RECEPTORS mechanical pinching cutting thermal hot cold injured polymodal all mechanical thermal plus chemicals released when tissue is pain is pure perception the STIMULUS is tissue damage Nociceptors respond to AND release chemical stimuli basis of inflammation pain sensitive cells spinal cord relay info to several areas of the brain pain pathways cross to a tract ascending the contralateral side of the spinal cord somatosensory cortex responds to painful stimuli memories of pain and signals that warn of impending pain cortex and cingulate cortex emotional associations central nuclei thalamus amygdala hippocampus prefrontal opioid mechanisms systems that are sensitive to opioid drugs and similar chemicals cannabinoids act mainly in the periphery of the body 3 Thursday March 27 y activating opiate receptors block the release of substance p in spinal cord in periaqueductal gray area of midbrain Gate theory spinal cord areas that receive messages from pain receptors also receive input from touch receptors and from axons descending from the brain descending pathways can keep CNS from receiving pain signals CNS activates neurons that release endorphins descending brainstem fiber excitatory opiate neuron inhibitory nociceptor excitatory placebo drug or other procedure with no pharmacological effect decreases pain perception by decreasing the brain s emotional response to pain perception NOT sensation itself decreases response in cingulate cortex but not in the somatosensory cortex non steroidal anti inflammatory drugs ibuprofen decrease chemicals that pester pain receptors chronic pain certain receptors become potentiated after an intense barrage of painful stimuli leads to increased sensitivity emotional pain increased activity in the cingulate cortex when someone felt left out of activity Itch is NOT A PAIN pain itch have an inhibitory relationship opiates increase itch while antihistamines decrease itch itch release of histamines by the skin 4 Temperature Thirst temperature regulation is one of body s biological priorities Thursday March 27 y basal metabolism energy used to maintain a constant body temp while at rest homeostasis temperature regulation and biological processes that keep certain body variables within a fixed range set point single value that body works to main Ex levels of water oxygen glucose calcium protein fat and acidity in the body negative feedback reduce discrepancies from the set point allostasis adaptive way in which the body changes its set point in response to changes in life or the environment poikilothermic body temp matches that of environment Ex amphibians reptiles most fish homeothermic internal physiological mechanisms to maintain an almost constant body temps Ex characteristics of mammals birds requires energy fuel sweating panting decreases temp increase temp is accomplished via shivering increase metabolism decrease blood flow mammals evolved to have a constant temp or around 37 C 98 F muscle activity warm as possible proteins in body break bonds lose properties at higher temps reproductive cells require cooler temps fever caused by bacterial and viral infections part of body defense against illness fever above 39 C 103F does more harm then good 5 Thursday March 27 y fever above 41 C 109F life threatening body temp regulation is depending upon preoptic area anterior hypothalamus POA AH POA AH monitors bodys temp by monitoring its own temp cells of POA AH receive input from temperature sensitive receptors in the skin water constitutes 70 of mammalian body water can be conserved by excreting concentrated urine decreasing sweat other autonomic responses most often water regulation is accomplished via drinking more water than we need and excreting the rest dehydration condition in which water or fluid loss far exceeds fluid intake the body becomes less able to maintain adequate blood pressure deliver sufficient oxygen nutrients to the cells and rid itself of wastes symptoms of dehydration it can be fatal thirst fatigue weakness decreased urination dark yellow of urine osmotic thirst thirst resulting from eating salty foods osmotic thirst occurs
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