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