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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 NOWAnswer questions #1&2 on your worksheets.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?How many things are going on here?

Watch the video and answer question #3 on your worksheets.

http://www.youtube.com/watch?v=8-KzaBISajE&NR=1

3How many things need to happen to allow the first ball to transmit the signal to the second ball over a long distance?

2131. The ball talks to the dominos2. The dominos talk to each other3. The dominos talk to the ball again

Answer question #4 on your worksheets.http://www.youtube.com/watch?v=8-KzaBISajE&NR=1

4

The axonThe 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?

The lipid membrane is NOT permeable to charged molecules.

Pores in themembranePores in themembraneWhat does this mean?But, its NOT impermeable either it has pores so charged ions can pass through.

Pores in themembranePores in themembraneIons on either side of the membranecan leak through the pores to reach equilibrium.

Pores in themembranePores in themembraneThere are sodium (Na+) ions on the outsideAnd potassium (K+) ions on the insideWhat does this mean?

Answer question #7 on your worksheets.

Pores in themembranePores in themembraneThe sodium (Na+) ions want to go insideAnd the potassium (K+) ions want to go outside

The pores are normally closed - butPores in themembranePores in themembraneSome sodium (Na+) ions can leak insideMore potassium (K+) ions can leak outside

Heres 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.

The pump puts Na+ back outsideThe pump puts K+ back insideThe axon puts a pump in its membrane

But the pump is better at pumping sodium back out than potassium back in. Na+ outsideK+ insideAnswer 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?

When the pump is working, there will be more Na+ and K+ on the outside of the axon.If we call outside zeroIs the inside more positive or more negative?

This means that there is also charge difference across the membrane.0 millivolts(0mV)-70 millivolts(-70mV)

-70mVWhy bother?

-70mVThe axon can harness this potential energy to produce a signal!

-70mVAnswer 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? -70mVMore positive (or less negative). But how???

We need to let Na+ inside the axon.

-70mVIf 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???

-70mV

The faucet is a Na+ channel that opens to allow Na+ to enter the axon. 1. Closed2. Open3. Closing4. Closed again-50mV

-70mV

1. Closed2. Open3. Closing4. 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?

1. Communication from the upstream connection causes the membrane to become less negative it depolarizes.2. This opens the voltage-gated Na+ channel3. Na+ enters the axon4. The axon depolarizes even moreWhat causes the membrane potential to changeso the Na+ channels can open? 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? 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

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

A Hint to what is happening at Step #5

What happens to the potassium ions?a) When the voltage-gated sodium channel opensb) When the voltage-gated sodium channel closes