The Nervous System and the Sodium-Potassium Pump

Transcription

1 The Nervous System and the Sodium-Potassium Pump 1. Define the following terms: Ion: A Student Activity on Membrane Potentials Cation: Anion: Concentration gradient: Simple diffusion: Sodium-Potassium Pump: Electrical gradient: 2. What are the predominant ions of the: a. extracellular (outside of cell) fluid/ ECF? b. Intracellular (inside of cell) fluid/icf? Materials: a white board with a line drawn across the middle (hot dog bun style) to represent the cell membrane - label the bottom half ICF and the top half ECF, four different colored beans (fill in chart below), colored pens to draw in rectangles for ion channels. Bean Type: Ion it represents: Na+ Cl - K+ Protein anion (A - )

2 Exercise 1: What happens if a membrane is freely permeable to all ions? Place 10 Na+ and 10 Cl- ions in the ECF. Place 10 K+ and 10 protein anions (A-) in the ICF. The ICF and ECF are the same size so they can hold equal amounts of ions. 1. Is the ECF electrically neutral? Is the ICF electrically neutral? 2. Is there an electrical gradient that would move ions from one compartment to another? 3. Assume that the membrane is freely permeable to all four ions. Is there a concentration gradient for: Na+ K+ Cl- A- 4. Now, rearrange the ions so that any concentration gradients are removed. This places the system in equilibrium. In the space below, draw the system in equilibrium: 5. What happens if a membrane is freely permeable to all ions? Exercise 2: What happens when a membrane is selectively permeable, allowing only certain ions to cross? From now on, assume that the membrane is impermeable to ALL ions unless a transport protein for a specific ion is placed on the membrane. (Transport proteins move ions and molecules across a membrane while using ATP= active transport). Place 10 Na+ and 10 Cl- in the ECF and place 10 K+ and 10 A- in the ICF. 6. Is the ECF electrically neutral? Is the ICF electrically neutral? 7. Is there an electrical gradient that would move ions from one compartment to another? 8. Can any ions cross the membrane using a concentration gradient? Why or why not?

3 9. Now place the rectangle for the K+ leak channel on the membrane in the open position. Can K+ now cross the membrane? Which direction will it move? 10. What force is moving the K+? 11. Move 2 K+ beans from the ICF to the ECF. What is the net electrical charge in the ECF? In the ICF? 12. Draw the cell and label the net charges for the ICF and ECF. 13. When there is an uneven distribution of ions between the ICF and ECF (as you have just created in your model), then the electrical gradient between the two compartments is known as the resting membrane potential. This is what a membrane potential really means: a. Resting = all living cells, even ones without electrical activity, maintain an electrical gradient. This is normal for all cells. b. Potential = the electrical and concentration gradients in a cell are sources of stored or potential energy. When oppositely charged particles move together, they release energy that opens voltage-gated protein channels and transport proteins. c. Membrane = here to remind you that there is a difference in charge between the inside and outside of the cell. It tells you the electrical charge of the ICF. d. So, what happens when a membrane is selectively permeable? Exercise 3: What happens once an electrical/concentration gradient exists between the ICF and ECF? Based on the results from exercise 2, you should have 2 K+ in the ECF and 8 K+ in the ICF. The K+ moved out of the cell with help from a leak channel and an established concentration gradient. 14. If the net charge inside the cell is now -2, in which direction would K+ move along its concentration gradient?

4 15. If more K+ moves outside of the cell along its concentration gradient, then does the ICF (resting membrane potential) become more negative or more positive? 16. Refer to p1052 in Campbell. If the resting membrane potential becomes more negative, then this is called. ( hyperpolarization / depolarization ) 17. On the graph below, draw what happens to the resting membrane potential (ICF) as K+ moves from the ICF to ECF. Refer to Campbell p1053. Label the hyperpolarization on the graph. 18. a) Now, rearrange your ions so that you have 12 Na+ and 12 Cl- in the ECF and 12 K+ and 12 protein anions (A-) in the ICF. Remove the K+ leak channel and replace it with a Na+ leak channel. b) Will Na+ move across the membrane? If so, in which direction will it move? 19. If Na+ moves, what will happen to the electrical neutrality of the model? (Realize that the equilibrium potential is the electrical charge inside of the cell that would exactly oppose a concentration gradient): (ICF more positive OR ICF more negative). 20. Now, move 2 Na+ ions from the ECF to the ICF. What is the net electrical charge in the ECF? In the ICF? 21. In what direction will Na+ move along its concentration gradient? 22. If more Na+ moves inside the cell along its concentration gradient, then does the ICF (resting membrane potential) become more negative or more positve?

5 23. Refer to p1052 of Campbell. If the resting membrane potential becomes more positive, then this is called. (hyperpolarization / depolarization) 24. On the graph below, draw what happens to the resting membrane potential (ICF) as Na+ moves from the ECF to ICF. Refer to page 1053 in Campbell. Label the depolarization on the graph. 25. So, what happens when an electrical and concentration gradient exist between the ICF and ECF? 26. In which cells and tissues does this occur? Excercise 4: What is an action potential? Refer to your Campbell biology book Ch 48 for this section. Start with p1049, Figure This is the structure of a vertebrate neuron. 27. Sketch the vertebrate neuron. In your diagram, label the dendrites, the axon, the cell body and use a red arrow to label signal direction.

6 28. What part of the neuron receives the electrical input and carries the signal to the cell body? 29. What part of the neuron carries the electrical signal away from the cell body? 30. Refer to page 1053 and fill in the graph below. Label the axes, the action potential, resting potential and threshold potential. 31. When these type of cells undergo action potentials, what exactly is happening to the ICF? Is it becoming more positive or more negative? 32. Does the ICF become hyperpolarized or depolarized? 33. What ions depolarize a cell membrane (ICF)? Where do they come from (inside or outside of the cell)? 34. What ions hyperpolarize a cell membrane (ICF)? Where do they come from (inside or outside of the cell)? 35. What is the purpose of a myelin sheath? How does it perform this task? Summary of Learning: *Distinguish between sensory neurons, inter-neurons, and motor neurons. What is a reflex arc? What role does acetylcholine play in all of this?