2. Physiology of the Nervous System

3. Ion channels Remember Ohm’s Law: I=E/R
When a channel opens, it has a fixed resistance.
Thus, each channel has a fixed current.
Using the patch-clamp technique, we can measure the current through individual channels

4. Ionic basis of Em NaK-ATPase pumps 3Na+ out for 2 K+ pumped in.
Some of the K+ leaks back out, making the interior of the cell negative

5. Gated channels: ligand-gated

6. Gated channels: voltage-gated

7. Gated channels: mechanically-gated

8. Physiology of Nerves
There are two major regulatory systems in the body, the nervous system and the endocrine system.
The endocrine system regulates relatively slow, long-lived responses
The nervous system regulates fast, short-term responses

9. Divisions of the nervous system

10. Neuron structure
Neurons all have same basic structure, a cell body with a number of dendrites and one long axon.

11. Types of neurons

12. Non-excitable cells of the nervous system

13. Structure of gray matter

14. Signal transmission in neurons

15. Membrane potential

16. Resting potential

17. Induction of an action potential I

18. Induction of an action potential II

19. Transmitter effects on Em
Most chemical stimuli result in an influx of cations
This causes a depolarization of the membrane potential
At least one transmitter opens an anion influx
This results in a hyperpolarization.

20. EPSPs and IPSPs
If the transmitter opens a cation influx, the resulting depolarization is called an Excitatory Post Synaptic Potential (EPSP).
These individual potentials are sub-threshold.
If the transmitter opens an anion influx, the resulting hyperpolarization is called an Inhibitory Post Synaptic Potential (IPSP
All these potentials are additive.

22. Signal integration

23. Signal integration cont.

24. Voltage-gated Na+ channels
These channels have two voltage sensitive gates.
At resting Em, one gate is closed and the other is open.
When the membrane becomes depolarized enough, the second gate will open.
After a short time, the second gate will then shut.

25. Voltage-gated K+ channels
Voltage-gated K+ channels have only one gate.
This gate is also activated by depolarization.
However, this gate is much slower to respond to the depolarization.

26. Cycling of V-G channels

27. Action potential propagation
When the V-G Na+ channels open, they cause a depolarization of the neighboring membrane.
This causes the Na+ and K+ channels in that piece of membrane to be activated

28. AP propagation cont.
The V_G chanels in the neighboring membrane then open, causing that membrane to depolarize.
That depolarizes the next piece of membrane, etc.
It takes a while for the Na+ channels to return to their voltage-sensitive state. Until then, they won’t respond to a second depolarization.

29. Changes in Em
When the V-G Na+ channels open, there is a rush of Na+ into the cell, making the inside positive.
The Na+ channels close at the same time the V-G K+ channels open.
When this happens, there is a rush of K+ out of the cell, making the inside more negative.

30. Synaptic transmission

31. Presynaptic inhibition

32. Presynaptic facilitation

33. Post-synaptic integration

34. Neural circuits I

35. Neural circuits II

36. Saltatory AP propagation in myelinated nerves

38. Myelination I
In the central nervous system, myelin is formed by the oligodendrocytes.
One oligodendrocyte can contribute to the myelin sheath of several axons.

39. Myelination II
In the peripheral nervous system, myelin is formed by Schwann cells.
Each Schwann cell associates with only one axon, when forming a myelinated internode.

40. Schwann cells cont.
In unmyelinated nerves, each Schwann cell can associate with several axons.
These axons become embedded in the Schwann cell, which provides structural support and nutrients.

41. White and gray matter in the nervous system

42. Structure of the spinal cord I
The CNS is made up not only of the brain, but also the spinal cord.
The spinal cord is a thick, hollow tube of nerves that runs down the back, through the spine.

43. Structure of the spinal cord II

44. Structure of the spinal cord III

45. Structure of the spinal cord IV