Brain&BehaviorTouch and PainTemperature&ThirstHungerSleep & Circadian rhythmsSex, Gender& hormonesThursday, March 27, yBrain&BehaviorTouch and Pain-Distortion due to variation in the size and density of sensory neuron "receptive fields"TouchTouch receptors:-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:-Pacinian corpuscle and ruffini endings1Thursday, March 27, y-strech-perception of the shape of a grasped objectReceptive Fields-receptive field: group of sensory neurons that converge on the same neuron in the 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-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 spinal nerves to the brain.-each spinal nerve has sensory component and a motor component & connects to a limited area of the body.-dermatome: skin are connected to or innervated by a single sensory spinal nerve.-they overlap & sensory info entering spinal cord travel in well defined&distinctpathways. (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 ratsPain-Pain: experience evoked by a harmful stimulus, directs our attention, and holds it2Thursday, March 27, y-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!-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-polymodal: all mechanical&thermal plus chemicals released when tissue is injured.-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 thatwarn of impending pain.-emotional associations: central nuclei, thalamus, amygdala, hippocampus, prefrontal cortex, and cingulate cortex.-opioid mechanisms: systems that are sensitive to opioid drugs and similar chemicals-cannabinoids act mainly in the periphery of the body.3Thursday, 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 receiveinput 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 painperception, 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 skin4Thursday, March 27, yTemperature&Thirst-temperature regulation is one of body's biological priorities-basal metabolism: energy used to maintain a constant body temp while at rest-homeostasis: temperature regulation and biological processes that keep certain bodyvariables 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, decreaseblood 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 good5Thursday, March 27, yfever 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 bodywater 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
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