Psych 330 1st Edition Lecture 4I. Action PotentialESPS(depolarization=excitement) with a threshold -threshold of 50, when threshold is reached=firingaction potential passes through acon to end to signal neurotransmitters to be released all or nothingdoesn’t reach threshold, doesn’t fireeflux of sodiumreverses polarity=action potentialII. Depolarizationwhen cells get excited=moving action potential closer to zero, ie. let NA in through gated channelsEPSP=excitatory postsynaptic potential(depolarization), gets excited because neurotransmitter binding; brief in response to stimulationmakes it more likely to reach action potentialIII. Hyper PolarizationIPSPinhibitory postsynaptic potentialpolarization further from zero> further from being excited -makes it less likely for it to reach action potentialIV. Repolarizationgetting ready to fire again, needs to return to resting state -potassium leaves the cell, hyperpolarizes=potential goes above 0 pumps out NA+, brings in K+while its transitioning back no more stimulation=absolute refractory period -refractorygoes below resting so its harder to stimulate, takes more to stimulateV. Summationeach cell has many synapsessummation=adding stimulation, always combination of excitatory and inhibitory messagessummation depends on how close the synapses are/how synchronized they aretemporal summationfiring needs to be close in time, bigger effect toward threshold for hyper/depolarizationspatial summation=how close the closes are physically, if synapses are on opposite sides they are less influentialVI. Axon Hillockaxon hillock=junction of axon to cell bodyEPSP is summer here>if reaches 50 axon hillock will fire action potentialall or nonesummed>hillock depolarized>action potential down axon if axons were myelinated a 100% signal would lose energy signal jumps from node to node, myelinated fibers in betweennodes of Ranvier=full of sodium channels that regenerate action potential needed to pass message onmyelin sheaths must be regulated because longer sheaths=message is lost, shorter sheaths=message takes longeraction potential> behavior? bunches of cells communicating in one direction, multiple cells fire collectively for muscles, chemical signal->electrical signal>to chemical signal from cell to