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_-60_ mV

The action potential: a review in 12 slides. A neuronal cell at rest. _-60_ mV. Ligand -gated Na + channel (for example). Voltage -gated Ca ++ channel. Ligand binds to the receptor and opens the channel. Sodium rushes in Close to the receptor.

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_-60_ mV

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  1. The action potential: a review in 12 slides A neuronal cell at rest _-60_ mV Ligand-gated Na+ channel (for example) Voltage-gated Ca++ channel Ligand binds to the receptor and opens the channel Sodium rushes in Close to the receptor

  2. K+ Cl- Na+ Cl- K+ Cl- Na+ Cl- Cl- K+ Cl- Na+ Cl- K+ Cl- Na+ Stage 1: an equal distribution of + and - ions across the membrane. Lipid bilayer 0 mV K+ Cl- Na+ Cl- K+ Cl- Na+ Cl- Cl- K+ Cl- Na+ Cl- K+ Cl- Na+ Na+ Cl- Na+ Cl- Na+ Cl- Na+ Cl- Cl- Na+ Cl- Na+ Cl- K+ Cl- Na+ Stage 2: The Na+/K+ antiporter kicks in and exchanges Na for K (assume 1:1 for demonstration purposes here). Na+/K+ 0 mV K+ Cl- K+ Cl- K+ Cl- Na+ Cl- Cl- K+ Cl- K+ Cl- K+ Cl- K+ This runs continuously

  3. Na+ Cl- Na+ Cl- Na+ Cl- Na+ Cl- Cl- Na+ Cl- Na+ Cl- K+ Cl- Na+ Stage 3a: K+ leak channels open up and potassium flows outside the cell (before view). Na+/K+ K+ 0 mV K+ Cl- K+ Cl- K+ Cl- K+ Cl- Cl- K+ Cl- K+ Cl- Na+ Cl- K+ Na+ Cl- Na+ Cl- Na+ Cl- Na+ Cl- Cl- Na+ Cl- Na+ Cl- K+ Cl- Na+ K+ K+ K+ K+ K+ K+ Stage 3b: K+ leak channels open up and potassium flows outside the cell (after view). Na+/K+ K+ -60 mV Cl- Cl- Cl- Cl- Cl- Cl- Cl- K+ Cl- K+ Cl- K+ Cl- K+ This runs continuously

  4. Na+ Cl-Na+ Cl- K+ Cl-Na+ Cl- Cl-Na+ Cl-Na+ Cl- Na+ Cl-Na+ K+ K+ K+ K+ K+ K+ Stage 4a: Ligand-gated sodium channel opens when ligand binds; Na+ flows into cell near the receptor site Na+/K+ K+ -60 mV Cl- Cl- Cl- Cl- Cl- Cl- Cl- K+ Cl-Na+ Cl- K+ Cl- K+ Cl- Cl- Cl- Cl- Cl-Na+ Cl-Na+ Cl- K+ Cl-Na+ K+ K+ K+ K+ K+ K+ Stage 4b: Na+ influx depolarizes the cell (more positive on the inside now) Na+/K+ K+ +40 mV Cl-Na+ Cl- Na+ Cl-Na+ Cl- Cl- Na+ Na+ Na+ Na+ Na+ Na+ Na+ Cl- K+ Cl- K+ Cl-Na+ Cl- K+

  5. Cl- Cl- Cl- Cl- Cl-Na+ Cl-Na+ Cl- K+ Cl-Na+ K+ K+ K+ K+ K+ K+ Stage 4b: Remember that the Na/K anti- porter is on the job!!! what happens? Why is the voltage now positive? Na+/K+ K+ +40 mV Cl-Na+ Cl- Na+ Cl-Na+ Cl- Cl- Na+ Na+ Na+ Na+ Na+ Na+ Na+ Cl- K+ Cl- K+ Cl-Na+ Cl- K+ Stage 2: The Na+/K+ antiporter kicks in and exchanges Na for K (actually moves 3Na+ out to 2K+ in) (ACTIVE transport) K+ leak channel re-sets the voltage (-60 mV) Na+ Cl- Na+ Cl- Na+ Cl- Na+ Cl- Cl- Na+ Cl- Na+ Cl- K+ Cl- Na+ Na+/K+ K+ Cl- K+ Cl- K+ Cl- Na+ Cl- Cl- K+ Cl- K+ Cl- K+ Cl- K+ This runs continuously

  6. Voltage redux: assume 1+ unit here = 10 mV K+ Cl- Na+ Cl- K+ Cl- Na+ Cl- Cl- K+ Cl- Na+ Cl- K+ Cl- Na+ Stage 1: an equal distribution of + and - ions across the membrane. Lipid bilayer 0 mV K+ Cl- Na+ Cl-K+Cl-Na+ Cl- Cl- K+ Cl- Na+ Cl- K+ Cl- Na+ K+ Cl- Na+ Cl- K+ Cl- Na+ Cl- Cl- K+ Cl- Na+ Cl- K+ Cl- Na+ K+ Stage 2: A single K+ Moves outside with No accompanying Cl- Lipid bilayer -10 mV Cl- K+ Cl- Na+ Cl-Na+ Cl- Cl- K+ Cl- Na+ Cl- K+ Cl- Na+

  7. Voltage redux: assume 1+ unit here = 10 mV K+ Cl- Na+ Cl- K+ Cl- Na+ Cl- Cl- K+ Cl- Na+ Cl- K+ Cl- Na+ K+K+ Stage 3: a second K+ moves outside the cell without an accompanying charge. -20 mV Lipid bilayer Cl- Cl- K+ Cl- K+ Cl-Na+ Cl- Cl- K+ Cl- K+ Cl- Na+ K+ Cl- Na+ Cl- K+ Cl- Na+ Cl- Cl- K+ Cl- Na+ Cl- K+ Cl- Na+ K+K+K+K+K+K+K+ Stage 4: A six K+ move outside with no accompanying Cl- -60 mV Lipid bilayer Cl-Cl-Cl-Cl-Cl-Cl-Cl- Na+ Cl- Cl- Na+

  8. Voltage redux: assume 1+ unit here = 10 mV K+ Cl-Na+ Cl- K+ Cl-Na+ Cl- Cl-Na+ Cl-Na+Cl- K+ Cl-Na+ K+K+K+K+K+K+K+ Stage 5: Note the Na+ gradient. Opening a ligand-gated sodium channel can destroy the voltage (and beyond) (Does K+ move?) -60 mV Lipid bilayer Cl-Cl-Cl-Cl-Cl-Cl-Cl- Na+ Cl- Cl- Na+ Under this scheme, how many Na+ must enter the cell to make it 0 mV? make it +40 mV? What would happen to the above diagram if 3 Cl- moved in? if 1 Cl- moved out?

  9. Voltage redux: assume 1+ unit here = 10 mV K+ Cl-Na+ Cl- K+ Cl-Na+ Cl- Cl-Na+ Cl-Na+Cl- K+ Cl-Na+ K+K+K+K+K+K+K+ Stage 5: Note the Na+ gradient. Opening a ligand-gated sodium channel can destroy the voltage (and beyond) (Does K+ move?) -60 mV Lipid bilayer Cl-Cl-Cl-Cl-Cl-Cl-Cl- Na+ Cl- Cl- Na+ Under this scheme, how many Na+ must enter the cell to make it +40 mV? Ten! Six would make it zero mV, while four more get you to +40 mV What would the voltage become if 3 Cl- moved in? -90 mV if 1 Cl- moved out? -50 mV

  10. A neuronal cell at rest _-60_ mV Ligand-gated Na+ channel Voltage-gated Ca++ channel Ligand binds to the receptor and opens the channel Sodium rushes in near the receptor

  11. Propagation of a voltage along the axon as a function of time The -60 mV resting potential is destroyed directionally from the site of the input signal to the end of the neuron.

  12. What happens at the “end” of the action potential

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