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Week 3 - Week 3 Missing notes A substance for people with...

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Week 3 1 1/28/08 Missing notes: A substance for people with high blood pressure – potassium chloride. Inject this substance into bloodstream, it will kill the person and it does not have to be very much. When extracellular molarity of potassium goes from 5 millimolar to 10 millimolar – it has profound effect on the resting potential of the cell. But 5 to 40/60 millimolar, increase in extracellular concentration of potassium – potassium can no longer leave the cell because it is compensating for the influx of sodium. It is not likely that it would actually be driven into the cell, but it will just prevent potassium from leaving. - Potassium can no longer leave the cell. This kills because it cannot return to the resting potential even though the cell firing is due to sodium coming in. In the normal course of activity of a neuron –there is a cell at rest and if you change the external concentration of potassium and increase it, then the cell is going to increase its resting potential. – because less potassium will leave the cell to make it negative. - If there is a series of stimuli and reach threshold, the only thing that will return the cell to rest is potassium leaving the cell. If the concentration of potassium is higher outside the cell, it will not be able to leave. The neurons fire once, and that is it. Effectively, it stops the heart. If you only use a little bit of K why does it still let potassium leave? You can’t prevent it from getting back to resting potential, you want enough potassium so that it won’t go back to its eq. - If you add K to outside to make concentration same inside as out, eq. potential = 0. - If there was a series of stimuli and reach threshold, the only thing that will let that reach resting potential will be potassium leaving the cell. The neurons fire once and can’t fire again, effectively stopping the heart. Recall : A voltage clamp stimulus. Two currents: a sodium current that opens quickly and diminishes. A potassium current that opens slowly but also closes slowly. There are two currents, the sodium that opens quickly and diminishes and the potassium current that is steady and stays open. The shape of the two lines describes the kinetics of the population of neurons. Voltage clamped vs Not clamped. Higher conductance of sodium and lower and steadier conductance of potassium.
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Action potentials What is happening at the axon hillock? Assume: the first event that leads to an action potential would be voltage-gated sodium channels opening. The property of the channels dictates the shape of the curves and the voltage at which they are gated dictates when that event will occur. The threshold line is dictated by the channels that are in that axon. The voltage at which they decide to open sets threshold .
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