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FSU PSB 2000 - Exam 3

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Brain and Behavior Exam 3Touch 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 shapeo Deep layers of receptors (Pacinian corpuscle/Ruffini endings): for stretch/perception of shape of grasped object• Receptive field: group of sensory neurons (each w different sensitivity to touch) that converge/overlap on spinal cordo 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 men• 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 braino Each spinal nerve has a sensory and motor component and connects to a limited area of bodyo Dermatomes: overlapping skin areas connected to or innervated by a single sensory spinal cordo 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 bodyo 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 ito Capsaicin (found in hot pepper)- stimulates some pain receptors that respond to acids, heat, or coldo Axon impulses carrying pain are slow (little to no myelination), motor responses are fast (brain processes quickly)o Mild pain triggers release of glutamate in spinal cord, stronger pain triggers release of glutamate and substance P• 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 sideo 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 midbraino Capsaicin: dumps substance P so have to remake it or can damage pain receptoro 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 perceptiono Pain signals ascend the pain pathway and reach conscious awareness in the thalamus and cortexo CNS activates neurons that block release of substance P, keeping pain signals from getting in• Placebo: drug/procedure with no pharmacological effecto Decrease pain perception by decreasing brains emotional response (in cingulate cortex not somatosensory)• Mechanisms in body that increase pain sensitivity: o Damaged/inflamed tissue release histamine (nerve growth factor) that increase response of nearby pain receptorso 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 resto 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 pointo 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 regulationo 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 pantingo 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 Fo Muscle activity is always ready for vigorous activity in warmer temperatureso Proteins do not


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