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27 Cards in this Set

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 What is the equation for Nernst potential? Ex=60/Z * log (Xo/Xi) what is the equation for driving force? RMP - Ex What has a greater driving force, Na or Ca? Ca What is the equation for the current of an ion species? V=IR Ix = (Em-Ex)* gx What can be said about ion currents at steady state? The sum of all currents must equal zero. (Em-Ex)*gx + (Em-Ey)*gx = 0 The ___ of an ion determines its contribution to the RMP relative permeability of the membrane what causes repolarization in an AP? Na channels close K channels open after a delay when do K channels close? when the membrane is hyperpolarized what causes the Na channel to go from open to inactivated? just a delay. once it is open, there is a probability that it will become inactivated. what is a voltage clamp? in a voltage clamp, the membrane potential is controlled. The current is then measured at different voltages. The current can tell what the conductance of the membrane is at that voltage. how is the opening of Na channels cyclical? channels open (increase in Na conductance) --> depolarization --> more channels open, etc what is accomodation? if the membrane is depolarized very slowly, it can be brought all the way to Na's reversal potential w/o causing a depolarization. depolarizing it slowly means that Na channels will open and deactivate a capacitor slows the rate at which ___ membrane potential can be changed what is myelin's effect on resistance and capacitance? increases resistance and decreases capacitance equation for the time constant? tm=rm*cm if the time constant is 50ms, how can an AP be generated in less than 1 ms? tm=rm*cm in an AP, the Rm goes way down with the opening of Na channels this decreases the time constant during the AP equation for the length constant lambda=square root of (rm/ri) why do fastest conducting neurons have the thickest diameter? the greater the diameter, the less the internal resistance lambda=square root of (rm/ri) lower the internal resistance, increase the time constant which will increase the conductance velocity: a large membrane resistance or a large internal resistance? large membrane resistance lambda=square root of (rm/ri) increase membrane resistance, increase length constant current is conducted axially rather than through membrane?? what causes the absolute refractory period? Na channels are inactivated open K channels oppose depolarization what causes the relative refractory period? Some Na channels are inactivated, and open K channels oppose depolarization. A strong artificial stimulus could get enough Na channels to open to create an AP what is local circuit propagation propagation in unmyelinated axons. what kind of resistance does myelin increase? membrane resistance - harder for current to leak out - increases length constant how does myelin have an affect on the time constant myelin does increase resistance which increases the constant however, offsetting this, myelin decreases capacitance, overall decreasing the time constant why does the AP move faster in myelinated axons? APs are only generated at the nodes. length constant is large enough to reach from node to node where are ion channels concentrated in a myelinated axon? at the nodes of ranvier what is charcot marie tooth disease a PNS demyelination diseas caused by a mutation in the gap junctions in schwann cells that allow nutrients to get through layers