D-CH3-Membrane_Potentials_LN_Spring_2007 - Prelude to...

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Prelude to Lecture (Membrane Potentials) Dr. Denison's Quick and Dirty Big Picture : All the cells in our body have charges lined up at the cell membrane – negatives on the inside, positives on the outside. Our cells are more negative inside than outside the cell. It happens because the Na + K + pump pumps more positive ions to the outside than positive ions to the inside of the cell and because K + , a positive ion, continually leaks out of the cell, leaving big molecules with negative charges in the cell - they are too big get out. (So the cell is negative inside, positive outside – but keep in mind these are very tiny charge differences.) This separation of charge is a good thing because we can use it for signals, like action potentials (nerve impulses). During an action potential the charges across the membrane reverse (it becomes positive on the inside of the cell and negative on the outside of the cell). There are other signals (graded potentials) in which the charges don't actually reverse (but the charge changes inside the cell). Action potentials are signals for long distances in the body, graded potentials are short distance signals. Graded potentials can cause action potentials. Most Important Reasons Why You Should Learn : Increases or decreases in K + concentration in the extracellular fluid can kill you. The change in extracellular K + from normal affects the resting membrane potential (the charge across the resting cell membrane) and excitability of cells. When you understand this lecture, you will understand how. Also, it's important to realize that movement of ions across membranes is the way you can send messages down nerve cells. (There are amazingly rapid ionic events happening during each nerve impulse. It's mind blowing.) Highlights of What We'll Cover :--Difference between the extracellular and intracellular fluids --Resting membrane potential --Graded potentials and action potentials - - Events of the action potential Membrane Potentials Lecture Notes ECF different from ICF K . - higher concentration ________ cell Na - higher concentration _______ cell . ECF = ISF + plasma N a + higher in K + higher in Na K pump - Na K ATPase (ase = enzyme, splits __________) .. pumps _________Na + out than K + in Cl - unequally distributed, more in _______ 0 (passive, generally not pumped) 23
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Proteins – anions (anion = negatively charged ion) More inside cell, too big to get out (trapped inside). Are also other anions inside cell (phosphate ions) Differences in Na and K concentrations maintained by Na K pump .. . . Na+ kept high outside (the Na+ that leaks in is ___________________) K+ kept high inside (the K+ that leaks out is ___________________) Importance: allows membrane to become electrically polarized Necessary for conduction of nerve impulses (Muscles have impulses too) Electrical potential (voltage difference exists across _______ our cell membranes; nerve cells and muscle cells use it for _________________. All cells in our bodies have it.
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This note was uploaded on 03/18/2008 for the course BLD 220 taught by Professor Doig during the Spring '08 term at Michigan State University.

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D-CH3-Membrane_Potentials_LN_Spring_2007 - Prelude to...

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