1. Neurophysiology Conduction, transmission and integration of neural signals Chapter 3

2. Summary of neural transmission l Resting potential and action potential l signal propagation l ionic bases of electrical potentials l neural integration

3. Review of neuron l Input zone (dendrites) l Integration zone (axon hillock) l Conduction zone (axon) l Output zone (axon terminals) l Secretory event

4. Resting potential l Definition of electrical potential Potential energy Electrical potential

5. Resting potential l Recording and reference electrodes l amplifier l oscilloscope Experimental setup

6. Resting potential Across the membrane

7. Changing membrane potential (creating unrest!)

8. Graded potentials (decremental conduction) stimulator

9. The action potential -subthreshold -threshold of excitation -overshoot -afterpotential

10. Propagation of the action potential -non-decremental conduction

11. The ionic basis of membrane potentials Diffusion gradients -substances move from areas of high concentration to areas of low concentration Electrostatic gradients -substances can carry charge (ions) -substances move towards areas of unlike charge Dynamic equilibrium -gradients can balance one another

12. The ionic basis of membrane potential A- = protein K+=potassium Na+=sodium Cl-=chloride +cations -anions

13. Dynamic equilibrium

14. Dynamic equilibria For some species of ion (such as potassium), the relative concentrations on either side of the membrane are pretty much mathematically predictable (Nernst equation) just based on the balance of electrostatic and concentration gradients. For others (such as sodium) this is not the case.

15. This can only mean…. The membrane is not equally permeable to all ions. At least….not all the time!

16. Nerve cell membranes are filled with interesting proteins

17. The disposition of ions in the resting nerve cell

19. Refractory periods Note the difference between closed and inactivated sodium channels -sodium channels only open briefly and then cannot open for some period of time (absolute refractory period)

20. The pufferfish as a neuroscientific weapon About three o’clock in the morning we found ourselves seized with an extraordinary weakness and numbness all over our limbs. I had almost lost the sense of feeling; nor could I distinguish between light and heavy bodies of such as I had strength to move, a quart pot full of water and a feather being the same in my hand….--Captain James Cook--

21. Conduction of action potentials in unmyelinated axons

22. Conduction of action potentials in myelinated neurons -faster, cheaper

23. Consequences of demyelination - Multiple sclerosis

24. Synopsis of synaptic action Transmitter release receptor action (metabotropic vs. ionotropic receptors) postsynaptic potentials (EPSP’s and IPSP’s)

25. The synapse

26. Electron micrograph of a synapse

27. Synaptic vesicles fuse with presynaptic membrane (movement of vesicles is caused by entry of calcium into presynaptic terminal

28. Freeze-fracture view of transmitter release

29. Receptors - a special kind of membrane channel

30. Ionotropic receptors

31. Metabotropic receptors -G-protein coupled

32. Varieties of postsynaptic potentials (PSP’s) l Excitatory (EPSP) l usually when receptor channels admit sodium l Inhibitory (IPSP) l usually when receptor channels admit chloride

33. Termination of synaptic action 1. Deactivation 2. Re-uptake by transporters

34. Neural integration Spatial integration -ripples can collide and combine

35. Neural integration Spatial integration -ripples can go up (excitatory) or down (inhibitory)

36. Neural integration Spatial integration -ripples can combine

37. Another look at spatial summation

38. Neural integration Temporal integration -ripples can combine to make bigger ripples