PHY122_L08 - PHY122 PHY122 Physics for the Life Sciences II...

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PHY122 PHY122 – Physics for the Life Sciences Physics for the Life Sciences II II Lecture 8 Currents and Resistance Note: Clicker Channel 21 09/22/2011 1 Lecture 8
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Electricity in the Body: Nerves Typical nerve cell: – Cell body: genetic control and energy management endrites: input of chemical stimuli across synapses Dendrites: input of chemical stimuli across synapses – Axon: propagation of the electrical stimulus 09/22/2011 2 Lecture 8
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Simplified electric model Membrane is a dielectric insulator ( κ 9 ) contains: Na + channels ody axon K + channels Na + -K + pumps body hi i l t f 3 N td 2 K t f 7 membrane 3.6 10 m  +Q S physio-chemical pump: transfers 3Na + out and 2K + in per transfer, leaving the cell inside at –70 mV with respect to the outside + + membrane V C –Q E R 3 6 cross section =0 + + + + + + E + + ~7 nm membrane d E 70 mV Schematic diagram of an ion of axon E 0 E =0 + + + 7 nm 10 MV/m 2 channel (Na + or K + ): 1. 4-6 homologous repeat domains, . uter vestibule, + + + + 09/22/2011 3 Lecture 8 2. outer vestibule, 3. selectivity filter, 5. phosphorylation site, 6. membrane when an ion channel opens, ions flow from the side with the higher concen- tration to the side with the lowest
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The Na+ The Na+-K+ Ion Pump K+ Ion Pump Ion pumps use cellular energy (ATP) to pump the ions against their concentra- tion gradient. The ion pump most relevant to the action potential is the sodium– potassium pump, which transports 3 Na + ions out of the cell and 2 K + ions in per transfer, i.e. a net +ve charge out … emf, with negative potential inside … As a consequence, the concentration of potassium ions K + inside the neuron is roughly 20× larger than the outside con- centration, whereas the Na + concentration outside is roughly larger than inside. One of the important functions of Na + -K + pump is to maintain the volume of the cell.
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PHY122_L08 - PHY122 PHY122 Physics for the Life Sciences II...

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