1. BBio 351 – February 22, 2016 Today’s outline Questions about membrane potential? (Worksheet/Sherwood 3.5) Two sides of the membrane Electrical and chemical gradients The Nernst equation: balancing electrical and chemical gradients A graphical approach to electrical and chemical gradients The Goldman-Hodgkin-Katz (GHK) equation: calculating membrane potential based on multiple ions Computer modeling of neurons Ion channels (Sherwood 4.1) Spread of electrical signals within neurons (Sherwood 4.2-4.3) Passive (not using voltage-gated channels, no action potentials) Active (using voltage-gated channels and action potentials)

2. Gradients (worksheet) vs. ion channels Basic properties of ion channels “Channel” vs. “carrier”/“transporter”

3. 2 main types of ion channels 10 th Martini, Figure 12-11

4. A voltage-gated sodium channel Image: ch.ic.ac.uk

5. Example of ion-selective channel: K + http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2003/popular.html

6. What is lidocaine and how does it work? Ricarda J.C. Hilf et al., Nature Structural & Molecular Biology 2010 [inside of cell] [outside of cell]

7. OK. Ion channels are open. Ions go in or out. Then what? “Passive” vs. “active” spread Sherwood Figure 4-13a

8. Passive spread of electrical signals Sherwood Fig. 4-3

9. Passive spread of electrical signals Lambda song: faculty.washington.edu/crowther/Misc/Songs/lambda.shtml

10. Sherwood Fig. 4-4: passive spread, continued

11. Active spread of electrical signals: action potentials! What kinds of ion channels are required? What kind of feedback is at work?

12. Action potential at one location Sherwood Figure 4-5

13. Threshold Freeman et al., Biological Science (2014), Fig. 46-14

14. Spread of action potential along axon Freeman et al., Biological Science (2014), Fig. 46-8

15. Saltatory conduction with myelin: active + passive spread Sherwood Figure 4-13a

16. Saltatory conduction with myelin: active + passive spread What does saltatory mean? What is myelin? What function does myelin serve? Exactly how does myelin accomplish this function?

17. Myelin and the length constant How does myelin affect R m and/or R i ? How does myelin affect λ? Multiple sclerosis (MS) leads to partial demyelination. How does MS affect λ?