4. Describe the importance of the Na/K pump in maintaining a high extracellular Na concentration and a high intracellular K concentration. How does the pump contribute to the resting membrane potential? 5. Draw an action potential on a separate piece of paper. Label the phases. (You do not have to turn in this drawing, but I encourage you to try and do this.) In the space below, describe the state of the Na and K voltage-gated channels at each phase: a. Resting membrane potential: b. Threshold: c. Rapid depolarization: d. Repolarization: e. Hyperpolarization: 6. Describe the DAG second messenger system (not the IP3 pathway) beginning with the ligand binding to a membrane receptor and ending with the response of the cell. 7. Lipophilic substances stimulate their target cells by binding to, 8. Hydrophilic substances stimulate their target cells by binding to 9. How do large, polar substances cross a cell membrane? 10. Fill in the chart below: Na+ concentration K+ concentration intracellular extracellular receptors. receptors.