1. Nerve physiology

7. 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

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

9. Types of neurons

10. Divisions of the nervous system

11. Non-excitable cells of the nervous
system

12. Structure of gray matter

13. Signal transmission in neurons

14. Resting potential

15. 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

16. Electrochemical Gradients
Figure 12.12

17.  Remember Ohm’s
Ion channels 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

18. Gated channels: ligand-gated

19. Gated channels: voltage-gated

20. Gated channels: mechanically-gated

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

22. Graded Potentials

23. Graded Potentials

25. 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

26. The Generation of an Action
Potential
Figure 2.16.1

27. Graded potentials
vs
Action Potential

30. 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,

31. The Generation of an Action Potential

32. Induction of an action potential I

33. Induction of an action potential II

34. 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.

35. 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.

36. Cycling of V-G channels

38. 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

39. 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.

40. Propagation of an Action Potential
along an Unmyelinated Axon

41. Saltatory Propagation along a
Myelinated Axon

42. Saltatory Propagation along a
Myelinated Axon

43. 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.

44. Synaptic transmission

45. γ 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

46. 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.

47. 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.

48. Post-synaptic integration

49. Signal integration

50. Signal integration cont.

51. Presynaptic inhibition

52. Presynaptic facillitation

54. Neural circuits I

55. Neural circuits II

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

57. 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.

58. White and gray matter in the nervous
system

59. 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.

60. Structure of the spinal cord II

61. Structure of the spinal cord III

62. Structure of the spinal cord IV