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A-Level Biology OCR A

Sodium Ions Potassium Axon Resting Membrane Potential Inside

Resting potential (-70mV) is maintained by the sodium-potassium pump (SOPI pump) actively transporting 3 Na+ out and 2 K+ in. Potassium ions diffuse out through open potassium channels, while gated sodium channels remain closed, resulting in a net negative charge inside the axon.

Resting potential (-70mV) is maintained by the sodium-potassium pump (SOPI pump) actively transporting 3 Na+ out and 2 K+ in. Potassium ions diffuse out through open potassium channels, while gated sodium channels remain closed, resulting in a net negative charge inside the axon.

Front Explain how resting potential is established/maintained
Back Resting potential:
  • SOPI pump is constantly actively pumping 3 sodium ions out & 2 potassium ions in
  • There is more sodium outside the membrane than inside axon cytoplasm & more potassium inside axon cytoplasm than outside the membrane
  • Potassium ions are able to diffuse out of the axon down their electrochemical gradient through the open potassium ion channels
  • Since the gated sodium ion channels are closed, sodium is not able to diffuse in
  • As result there are more psoitively charged ions outside axon than inside, creating resting potential across membrane of -70mV (inside negative due to organic anions)

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