Bio 45 - 1) A cell usually rests at -70mV but this charge...

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1) A cell usually rests at -70mV but this charge can change between -40mV and -90mV depending on certain factors. Macromolecules such as Nucleic Acids, Proteins, and Carbohydrates tend to be more copious inside the cell rather than outside. These contain a net negative charge and since they are to big too move outside, they remain inside as fixed anions. Furthermore, the Sodium (Na) Potassium (K) pump sends out 3 Na+ for every 2 K+ it brings in. As more Na+ make their way to the outside than K+ come in, the inside of the cell becomes relatively more negative. In addition to the pump, ion leak channels, many of which are specific to the transport of K+, make it even easier for positive ions to leave the cell than get in. Few Na+ leak channels exist so even if they want to be in proximity with the negative, fixed anions, so few can get in that the charge is hardly changed. 2) When the membrane potential depolarizes and hits its threshold, a nerve impulse, known as action potential, occurs. If a cell’s negativity reaches about -55mV, it opens up its voltage-gated ion channels to let the flow of Sodium in so that Potassium can flow out faster along its concentration gradient. CL- also flows into the cell in an attempt to hyperpolarize the cell. The huge influx of Na+ is at first counter-intuitive, but this depolarization is only done so that the sodium potassium pump can go into affect as K+
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This note was uploaded on 09/27/2011 for the course BIOL 101 taught by Professor Fevzidaldal during the Fall '08 term at UPenn.

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Bio 45 - 1) A cell usually rests at -70mV but this charge...

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