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| Question | Answer |
| Electrochemistry: How electrical events in the cell are measured | - Intracellular- using an electrode inside the cell. Useful for understanding ionic mechanisms taht go across cell membranes, as well as what excites/inhibits it. - Extracellular- using an electrode on the outside of the cell. Has a smaller amplitude on a graph of action potential. - Patch clamping- using an electrode sealed to the cell surface. Allows you to measure activity in ion channels. No current = channel is closed. * Electrical recordings usually take place using a fluid-filled glass capillary tube microelectrode * Phase contrast optics are used to see cells with the microscope, could not be seen under normal light |
| Stages of electrical charges in the cell | - At rest: inner membrane of the cell is negatively charged with respect to the outside, usually around 70Mv. - When action potential is activated: becomes depolarised, the inner membrane becomes positively charged compared to the outside |
| How electrochemical gradients are established | 1. Sodium-potassium ATPase pump produces ATP to drive ions across the membrane. 2. Restricted movement through ion channels 3. Membranes of cells are able to store charges on both their inner and outer surfaces. |
| Resting membrane potential | - Involves ion pairs; Cl- and K+. - To begin with, there are more of these ions on the inside of the cell than outside - As potassium channels open, K+ moves down the concentration gradient to the outside, where it is attracted to the surface of the membrane, which attracts K+ to the surface of the inside of the membrane. - As this occurs, charge decreases and rearrange around the surface of the membrane, resulting in a potential of -90mV from the shell of charge around the membrane, although the charge of the fluid is still equal. - Sodium/potassium pump maintains this by pumping k+ in and Na out. The restricted ion movement due to closed channels maintains this difference. |
| Work done at the membrane | - Charge separation requires work, which is measured in terms of volts. The more charges are separated at the membrane, the more work done. - The amount of work done at the membrane can be calculated from the conc gradient: *conc gradient for + ions= conc of an ion outside the cell/conc of an ion inside the cell *Conc gradient for - ions= conc of ions in/conc of ions out - The membrane voltage due to an ion can then be calculated using the nernst equation: E(voltage)=59(mv)xlogc(out)/c(in) |
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