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FSU PSB 2000 - Brain and Behavior 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 (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 in CNS 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 shape)o 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 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 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 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 cortexo 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)- 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 coldo Axon impulses carrying pain are slow (little/no myelination) but 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 Substance P results in increased sensitivity to pain• Pain receptors: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 braino From medulla to cerebral cortex: touch & pain represented on contralateral sideo 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 paino Emotional associated parts: central nuclei of thalamus, amygdala, hippocampus, prefrontal cortex, cingulate cortex • Pain control: o Activating opioid receptors blocks release of substance P in spinal cord & periaqueductal gray area in the midbraino Capsaicin: dumps substance P so have to remake opioid mechanisms or can damage pain receptoro Cannabinoids: chemicals related to marijuana that block certain types of pain (mainly in periphery of body) • 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 perceptiono Pain signals ascend the pain pathway and reach conscious awareness in the thalamus and cortexo “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• 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 feels emotionally hurt • Itch (like an anti-pain): caused by release of histamineso Activates distinct pathway in spinal cord to brain that travels very slowly- pain/itch have inhibitory relationshipo Opiates increase itch and decrease pain• Ticking (poorly understood): laughing is not normal laughter (doesn’t predict subsequent laughter) Temperature and thirst• Body and behavioral regulation of temperature existso 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 resto 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 pointo Allostasis (opposite of homeostasis): way that body changes its set point in response to life/environment changes • Poikilothermic (cold blooded: amphibians/reptiles/most fish): body temperature that matches that of its environment o Organism lacks the internal, physiological mechanisms of temperature regulationo Temperature


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