It partially depolarizes and makes the membrane less

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It partially depolarizes and makes the membrane less negative(or more positive).Partially depolarizes and makes membrane less negativeCauses depolarization (but not to -55 mV)Single excitatory stimulus usually does not initiate nerve impulse but membrane is closerto the threshold and more likely to reach threshold with next excitatory stimulusYou can also go negative causing…Inhibitory stimulus - Increases K+outward or increases Cl-(outside)inwardMakes membrane more negative(adding more negatives to the inside)Makes the membrane hyperpolarized (as low as -90mV) (makes it hard to get to thethreshold of -55mV)Generation of action potential is now more difficultMust add up all the excitatory and inhibitory stimuli (summation) that are influencing theneuron to determine if an action potential will be sent(Fig 11.18)They try to fight to cancel each other out.. like an election. If you have enough yesyou get an action potential, but if you have to many nos then nothing happens.Get the membrane potential high enough to hopefully have an action potential.Action PotentialsSingle stimulus is not good enough twice one after another causing a membrane potentialthen increasing enough to have enough to get to -55 and have an action potential
Action Potential (AP) = rapid change in membrane potential (polarity) that can spread downthe length of the axon .can only happen in axon then spread down the length of the axonThe membrane will depolarize and then repolarizeOnly muscle and neurons can produce an APOnly muscles and ------ have voltage gated ----10:50 am 4/2In neurons, an AP lasts about 1 ms or lessPropagation of APs down axons = nerve impulsesSteps in generating an Action Potential(Focus Figure 11.2)DepolarizationWhen a stimulus is applied, if the sum of stimuli is excitatory (mechanical gated orchemical gated ion channels open and cause a net flow of Na+into the cell) anddepolarization occurs to threshold potential (threshold = -55mV)At -55 mV, voltage gated Na+channels open and Na+rushes in (Na+inflow), making theinside of the cell positiveOnly 3 stages closed, open , or inactiveThis is the depolarization (Na+inflow) phase = normal polarized state is reversedInside = (+) outside= (-)K+is inside, Na+is inside, Inside = (+)Repolarization - membrane potential returns to a negative valueRepolarization is due to K+ions flowing outward (K+outflow) through voltage gated K+channelsInactive- closed and cannot open- only thing that can reactivate them is a rapid drop inpolarization and time.Voltage gated Na+channels inactivate and closeVoltage-gated K+channels open in response to positive membrane and remain open untilmembrane potential returns to a negative valueIon distribution is reverse of that at restingInside = (-)End of repolarization -K+ is outside, Na+ is inside, Inside = (-)Refractory Period - period of time during which an excitable cell cannot generate anotheraction potential(Fig 11.13) its like running a marathon you cant do two at once.

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Term
Summer
Professor
brown
Tags
Biology, Homeostasis, RNA, Lecture, Notes, Study, Chapter 11, Nerves

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