1. Nerve physiology

2. 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

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

4. Types of neurons

5. Divisions of the nervous system

6. Non-excitable cells of the nervous system

7. Structure of gray matter

8. Signal transmission in neurons

9. Resting potential

10. 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

11. Electrochemical Gradients
Figure 12.12

12. 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

13. Gated channels: ligand-gated

14. Gated channels: voltage-gated

15. Gated channels: mechanically-gated

16. Graded potential A change in potential that decreases with distance
Localized depolarization or hyperpolarization

17. Graded Potentials

18. Graded Potentials

20. Action Potential
Appears when region of excitable membrane depolarizes to threshold
Steps involved
Membrane depolarization and sodium channel activation
Sodium channel inactivation
Potassium channel activation
Return to normal permeability

21. The Generation of an Action Potential
Figure

22. Graded potentials vs Action Potential

25. Characteristics of action potentials
Generation of action potential follows all-or-none principle
Refractory period lasts from time action potential begins until normal resting potential returns
Continuous propagation
spread of action potential across entire membrane in series of small steps
salutatory propagation
action potential spreads from node to node, skipping internodal membrane

26. The Generation of an Action Potential

27. Induction of an action potential I

28. Induction of an action potential II

29. 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.

30. 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.

31. Cycling of V-G channels

33. 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

34. 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.

35. Propagation of an Action Potential along an Unmyelinated Axon

36. Saltatory Propagation along a Myelinated Axon

37. Saltatory Propagation along a Myelinated Axon

38. 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.

39. Synaptic transmission

40. g Aminobutyric Acid Also know as GABA Two know receptors for GABA
Both initiate hyperpolarization in the post-synaptic membrane
GABAA receptor allows an influx of Cl- ions
GABAB receptors allow an efflux of K+ ions

41. 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.

42. 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.

43. Post-synaptic integration

44. Signal integration

45. Signal integration cont.

46. Presynaptic inhibition

47. Presynaptic facillitation

49. Neural circuits I

50. Neural circuits II

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

52. 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.

53. White and gray matter in the nervous system

54. 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.

55. Structure of the spinal cord II

56. Structure of the spinal cord III

57. Structure of the spinal cord IV