Week 3 Answers

Week 3 Answers - BILD 2, Professor Fortes TA: Anna Gruzman (

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BILD 2, Professor Fortes Handout 2 TA: Anna Gruzman ( agruzman@ucsd.edu ) 10/12/10 Electrochemical Gradients: 1. In order to cause depolarization what ion channels would you have to open in a cell membrane? What are the forces driving this (Hint: What is the resting membrane potential of the cell)? A: The resting membrane potential of a cell is about -70mv. Now what does this mean? We learned last week about concentration gradients which are a result of an unequal concentration of ions or solute inside and outside the cell. In addition to that, for charged ions there is an electrical gradient. We all know that opposite charges attract and same charges repel. Since the inside of the cell is negative from an electrical standpoint, positive charges ( potassium, calcium, sodium) want to go in and negative charges ( Chlorine) want to go out. This, however, is not the whole picture because we also have concentration gradients caused by various degrees of permeability. There is more Sodium, Chlorine and Calcium outside of the cell and way more Potassium inside the cell. So What? Well, let’s now look at the combination of these different forces. Sodium: Both forces direct into cell. Chlorine: Forces in opposite directions (Electrical out and concentration in) Potassium: Forces in opposite directions (Electrical in and concentration out) Calcium: Both forces direct into the cell. So what wins? This is known as the equilibrium potential for each ion. (Eion - The voltage difference necessary to counterbalance the concentration gradient for a specific ion) The combination of all these contributing equilibrium potentials, when also taking permeability into account, establishes the resting membrane potential of the cell. (-70 mv) – This is calculated by the Nernst equation (see page 1051) Depolarization: involves making the cell more positive (or less negative depending on
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This note was uploaded on 02/05/2011 for the course BILD 2 taught by Professor Schroeder during the Spring '08 term at UCSD.

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Week 3 Answers - BILD 2, Professor Fortes TA: Anna Gruzman (

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