1. There are blue molecules on the left red molecules on the right. They are separated by a barrier that is permeable to both blue and red. 1) What happens next? Why? 2) How can you maintain more blue molecules on the left and more red molecules on the right? DO NOW Answer questions #1&2 on your worksheets.

2. Put in a pump that would pump the blue molecules to the left and the red molecules to the right. How can you maintain more blue molecules on the left and more red molecules on the right?

3. How many things are going on here? Watch the video and answer question #3 on your worksheets.

4. How many things need to happen to allow the first ball to transmit the signal to the second ball over a long distance? 2 1 3 1. The ball talks to the dominos 2. The dominos talk to each other 3. The dominos talk to the ball again Answer question #4 on your worksheets.

5. The axon The axon and its lipid membrane The axon is like a cylinder surrounded by a plasma membrane. Answer question #5 on your worksheets. Is a lipid membrane permeable to charged molecules?

6. The lipid membrane is NOT permeable to charged molecules. Pores in the membrane Pores in the membrane What does this mean? But, it’s NOT impermeable either – it has pores so charged ions can pass through.

7. Pores in the membrane Pores in the membrane Ions on either side of the membrane can leak through the pores to reach equilibrium.

8. Pores in the membrane Pores in the membrane There are sodium (Na+) ions on the outside And potassium (K+) ions on the inside What does this mean? Answer question #7 on your worksheets.

9. Pores in the membrane Pores in the membrane The sodium (Na+) ions want to go inside And the potassium (K+) ions want to go outside

10. The pores are normally closed - but Pores in the membrane Pores in the membrane Some sodium (Na+) ions can leak inside More potassium (K+) ions can leak outside

11. Here’s an analogy: You buy a house with a basement. It rains. Water gets in. What do you do next? Put in a pump to get the water out.

12. The pump puts Na+ back outside The pump puts K+ back inside The axon puts a pump in its membrane

13. But the pump is better at pumping sodium back out than potassium back in. Na+ outside K+ inside Answer question #8 on your worksheets. When the pump is working, will the inside of the axon be more positive or more negative relative to the outside?

14. When the pump is working, there will be more Na+ and K+ on the outside of the axon. If we call outside zero Is the inside more positive or more negative? This means that there is also charge difference across the membrane. 0 millivolts (0mV) -70 millivolts (-70mV)

15. -70mV Why bother?

16. -70mV The axon can harness this potential energy to produce a signal!

17. -70mV Answer question #9 on your worksheets. If we want to harness this potential energy to produce a signal, should the inside of the axon become more or less positive?

18. -70mV More positive (or less negative). But how??? We need to let Na + inside the axon.

19. -70mV If you want to take a shower – what do you do ? Turn on the faucet!!!! How do we make the inside of the axon more positive???

20. -70mV The faucet is a Na + channel that opens to allow Na+ to enter the axon. 1. Closed 2. Open 3. Closing 4. Closed again -50mV

21. -70mV 1. Closed 2. Open 3. Closing 4. Closed again -50mV Answer question #10 - 12 on your worksheets. - How is turning on the shower faucet analogous to harnessing the energy at the membrane? - What happens to the Na+ ions when the channels are open? - Once the Na+ channels close, are the Na+ ions trapped in the axon?

22. 1. Communication from the upstream connection – causes the membrane to become less negative – it depolarizes. 2. This opens the voltage- gated Na+ channel 3. Na+ enters the axon 4. The axon depolarizes even more What causes the membrane potential to change so the Na + channels can open?

23. When the inside of the axon becomes very positive (depolarized), the gate shuts and no more Na + can enter. Then what? What happens to the potassium ions?

24. When the inside of the axon becomes very depolarized, the gate shuts and no more Na+ can enter. The K+ channel opens, so K+ can leave the axon quickly. Answer question #13 on your worksheet. Then the K+ channel opens, and K+ can leave the axon quickly

25. Depolarization of the membrane is called the Action Potential. 1.The membrane is at rest. More Na+ is outside the cell. 2. The voltage-gated Na+ channel opens. Na+ enters the axon. 3. The voltage-gated Na+ channel closes and the voltage-gated K+ channel opens. 4. K+ ions leave the axon. 5. Homework: Can you predict what is happening here?

26. Homework A Hint to what is happening at Step #5… What happens to the potassium ions? a) When the voltage-gated sodium channel opens b) When the voltage-gated sodium channel closes