img103 - m u.7 Hui-u"I“ u —I*lmmhmh Inn-ya...

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Unformatted text preview: m, u _, .7 Hui-u "I“ u —I- *lmmhmh Inn-ya..- tum-Ilium Dhaka-chad b- in” . ' — U— Mam-car , u—n --- “"‘"‘°"‘ : "'— err-mumm- h-l- inlet: 0 . DWI-ewifllhhn “mm. o mhan-tb “Mb“ Mil-MW -~ 8 smallerions. Muesli-I‘m __ ' mum w my“ Oman-lashing .- om—mhhmhm u—n-n m-I—mbmmhd unnu- ommuamwnm oummmum mum-”WM mhwlllp-Ilihflh than it will be drawn back in. “and.“ it‘ll nun-u“ h ‘- humu- Page 2 of 5 Main—h- Drawn-amnesia-“ m chum—mum—muhn lamina—hm Ar (\20\ r 7 . v \L (((ml Rb G0 to the Next Screen: The sodium and potassium channels responsible for resting membrane potential are leak channels. Leak channels are always open. Because there are many more potassium leak channels than sodium channels inserted into the plasma membrane a cell is many time more permeable to potassium than to sodium. In fact a cell membrane iglifimmpemeablemmuummm sodium; Permeability of a cell depends on the number of ion charmels for that ion and the ease with which ions move through their specific ion charmels. Some ions are big and do not move through as quickly as Go to the Next Screen: To understand why a resting membrane potential is approximately -70mV we have to go back and discuss concentration and electrical gradients again. We have to consider both a chemical gradient and an electrical gradient when we are dealing with ions. Since potassium is in higher concentration inside the cell potassium will want to leak out of the cell (go down its chemical gradient). G0 to the next screen: Because potassium is an ion, when it moves down its chemical gradient it carries its +ve charge with it making the inside of the cell slightly less positive relative to the outside. Go to the next screen: The resting membrane potential is negative and this creates an electrical force that pulls potassium back into the cell. However, the chemical gradient pulling potassium out of the cell is greater than the electrical gradient pulling it back in. The electrochemical gradient is outside the cell so potassium will continue to leak out of the cell faster Go to the Next Screen: When you add the chemical and the electrical force together the force is called the electrochemical gradient. Let’s assume for now that the cell membrane is only permeable to potassium. The equilibrium point between the chemical force pulling potassium out and the electrical force pulling potassium back in' is when the membrane potential rs around -94mV (1;: ~94mV). At this point the chemical force equals the electrical force” There is no net flux of potassium across the cell membrane. ...
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