How is directional selection related to evolution?
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An action potential involves potassium ions moving <u>outside </u>the cell and sodium ions moving <u>inside </u>the cell.
<h3>how does it action potential work?</h3>Neurons have a negative concentration gradient most of the time, meaning there are more positively charged ions outside than inside the cell. This regular state of a negative concentration gradient is called resting membrane potential. During the resting membrane potential there are:
- more sodium ions
outside than inside the neuron
- more potassium ions
inside than outside the neuron
The concentration of ions isn’t static though! Ions are flowing in and out of the neuron constantly as the ions try to equalize their concentrations. The cell however maintains a fairly consistent negative concentration gradient (between -40 to -90 millivolts). How?
- The neuron cell membrane is super permeable to potassium ions, and so lots of potassium leaks out of the neuron through potassium leakage channels (holes in the cell wall).
- The neuron cell membrane is partially permeable to sodium ions, so sodium atoms slowly leak into the neuron through sodium leakage channels.
- The cell wants to maintain a negative resting membrane potential, so it has a pump that pumps potassium back into the cell and pumps sodium out of the cell at the same time.
Learn more about action potential
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