1. Chapter Outline
12.1 Basic Structure and Functions of the Nervous System
A. Overall Function of the N.S. & Basic Processes Used
B. Classification of the Nervous System
Histology of Nervous System
A. Neuroglia Cells
B. Neurons
C. Types of Neurons
12.4 The Action Potential
A. Electrically Active Cell Membranes
B. Membrane Potentials That Act As Signals
C. Graded Potentials (See Text section 12.5)
* D. Action Potentials
12.5 Communication Between Neurons
A. Basic Concepts and Terms
B. Synapses
Neurotransmitter Systems
12.3 The Functions of the Nervous System– How the Parts Work Together

2. 12.4 The Action Potentials … E. Action Potentials (AP)
1. Basic Concepts
a. Cells:
Initiated by:
Threshold: Membrane
depolarized by 15 to
20 mV
Myelinated and
Unmyelinated
(see diagram next slide)
Graded Potential
Action Potential
Neurotransmitter
Dendrites
Subthreshold stimulus is not detected

3. Non-Myelinated Axon
Myelinated Axon

4. 12.4 The Action Potentials … D. Action Potentials (AP) …
1. Basic Concepts …
e. Start & End Locations:
Type of Gated Channel:
Ions involved
h. All or None:
Graded Potential
Action Potential GP
Neurotransmitter
Dendrites

5. 2. OVERVIEW OF MECHANISMS a. Graded Potential  GP
Action Potential
Neurotransmitter
Section of Membrane
Dendrites
2. OVERVIEW OF MECHANISMS
a. Graded Potential 
b. At Axon Hillock: Small Section of Membrane
Depolarization– Na+ in
Repolarization—K+ out
Hyperpolarization– more K+ out
Return to Resting State– Na-K Pump
c. Adjacent chunks of membrane: stimulated one after another, each following above actions
d. When end is reached: Neurotransmitter carries message across to next neuron

6. The big picture Action Potentials … 1 2 3 3 4 2 1 1 4 Resting state
Depolarization 3
Repolarization 3 4
Hyperpolarization
Membrane potential (mV) 2
Action
potential
Threshold 1 1 4
Time (ms)
Figure (1 of 5)

7. Action Potentials … Unmyelinated Axons …
3. Types of Voltage-gated Channels
a. Na+ Channel has two Voltage gates
ACTIVATION
INACTIVATION
Function:
For Na+ to enter cell:
b. K+ Channel has one Voltage gate
Is Activating and:

8. 4. Initiating Action Potential– Details a. Resting State of Channels
4. Initiating Action Potential– Details a. Resting State of Channels Na+ activation gate: closed Na+ inactivation gate open K+ activation gate: closed
Takes 2 milli seconds
Na+
Sodium
channel
Potassium
channel
Activation
gates K+ 1
Resting state
Inactivation gate

9. Action Potentials … b. Depolarizing Phase
a. Initiated by:
b. At threshold:
c. Na+ flows in and membrane becomes:
d. End Point mVolts:
e. Restoration to Resting State:
Na+ 2
Depolarization K+

10. Repolarization c. Repolarizing Phase a. K+ Activation Gate Threshold:
b. K+:
c. Potential: is restored at:
d. K+ gates: slowly closing
Na+ K+ 3
Repolarization

11. Action Potentials … d. Hyperpolarization
a. K+ gates:
b. Excess K+:
c. Undershoot to:
K+ channels:
Na channels:
Na+ K+ 4
Hyperpolarization

12. Action Potentials … e. Resting State Restored
Na+-K+ Pump:
Leakage Channels

13. Generation of an Action Potential

14. The AP is caused by permeability changes in the plasma membrane3
Action
potential
Membrane potential (mV)
Na+ permeability 2
Relative membrane permeability
K+ permeability 1 1 4
Time (ms)
Figure (2 of 5)

15. 5. Propagation of the Action Potential– a. Nonmyelinated Axon
Moves in: one direction:
Continuously
Local Current generated: Na+ that have entered the axon move horizontally towards the more negative adjacent section of the membrane:
Na+ Channels of adjacent section of membrane:
5. Positive Feedback Cycle:

16. APs self-propagate – once started, all voltage channels open like dominoes (all or none)
at 2 ms
Voltage
at 0 ms
Voltage
at 4 ms
Recording
electrode
(a) Time = 0 ms. Action
potential has not yet
reached the recording
electrode.
(b) Time = 2 ms. Action
potential peak is at the
recording electrode.
(c) Time = 4 ms. Action
potential peak is past
the recording electrode.
Membrane at the
recording electrode is
still hyperpolarized.
Resting potential
Peak of action potential
Hyperpolarization

17. Propagation of an Action Potential in Unmyelinated axons

18. 1. Location of channels: 2. AP generate at: 3. 30 times faster
Action Potentials … Propagation of an Action Potential … b. Myelinated Axon = Saltatory Conduction
1. Location of channels:
2. AP generate at:
times faster
SHOW REST OF VIDEO

19. Unmyelinated axon Stimulus Voltage-gated ion channel Stimulus
Node of Ranvier
Myelin
sheath
1 mm
Myelin sheath

20. Propagation of an Action Potential in Myelinated axons

21. Action Potentials … 6. Characteristics of Action Potentials
a. Refractory Period:
i. Absolute Refractory Period =
Na+ channels are:
ii. Relative Refractory Period:
Na+ Channels:
Stimulus:
** Diagram on next slide

22. Threshold elevated, only exceptionally strong stimuli cause APs
Absolute refractory
period
Relative refractory
period
Nerve cannot fire,
Threshold elevated, only exceptionally strong stimuli cause APs
Depolarization
(Na+ enters)
Repolarization
(K+ leaves)
After-hyperpolarization
Stimulus
Time (ms)
Figure 11.14

23. Action Potentials … b. Coding for Stimulus Intensity
Strong stimuli:
Intensity determined by:
AP Frequency
Stimulus Strength

24. Action Potentials … c. Conduction Velocity
Diameter of Axon:
Myelinated or not:
Summary of GP vs AP

25. Action Potentials … 7. Multiple Sclerosis (MS)
STUDENTS DO: Text page 488

26. 12. 5 Communication Between Neurons A
12.5 Communication Between Neurons A. Graded Potentials see previous section =

27. Nerve Impulses– within and between neurons
Neurotransmitters
Synapse

28. A. Types of Synapses Chemical: Basic Components (Text p. 502)
Electrical:
Chemical:
Basic Components (Text p. 502)
presynaptic element
neurotransmitter in vesicles
synaptic cleft
receptor proteins
postsynaptic element
neurotransmitter elimination or re-uptake

29. 12.5 Communication between Neurons– The Synapse …
B. Chemical Synapses– details
Drug (legal & illegal) Affects–:
Addiction is due to:

30. Not common or well understood
B. Chemical Synapses– details … 2. Parts of Presynaptic and Postsynaptic Neurons involved
Axodendritic
synapses
Dendrites
Axosomatic
synapses
Cell body
Axoaxonic synapses
(a)
Axon
Not common or well understood
Axon
Axosomatic
synapses
Cell body (soma) of
postsynaptic neuron
(b)

31. Action potential arrives at axon terminal.
B. The Chemical Synapse …
3. Steps of Presynaptic Neuron communication with Postsynaptic Neuron
Presynaptic neuron
Presynaptic neuron a
Postsynaptic neuron
Action potential arrives at axon terminal.
Mitochondrion
Ca2+
Ca2+
Ca2+
Ca2+
Synaptic cleft
Axon terminal
Synaptic vesicles
Postsynaptic neuron
Figure 11.17, step 1

32. The Chemical Synapse Ca2+ Ca2+ Ca2+ b Figure 11.17, step 2
Presynaptic neuron
Presynaptic neuron
Postsynaptic neuron
Ca2+
Mitochondrion
Ca2+
Ca2+
Ca2+
Synaptic cleft
Axon terminal
Synaptic vesicles
Postsynaptic neuron b
Voltage-gated Ca2+ channels open:.
Figure 11.17, step 2

33. The Chemical Synapse c Synaptic vesicles Figure 11.17, step 3
Presynaptic neuron
Presynaptic neuron
Postsynaptic neuron
Synaptic vesicles
Mitochondrion
Ca2+
Ca2+
Ca2+
Ca2+
Synaptic cleft c
Ca2+ entry causes:
Axon terminal
Postsynaptic neuron

34. The Chemical Synapse d Figure 11.17, step 4 Presynaptic neuron
Postsynaptic neuron
Mitochondrion
Ca2+
Ca2+
Ca2+
Ca2+
Synaptic cleft
Axon terminal
Synaptic vesicles
Postsynaptic neuron d
Neurotransmitter:
Figure 11.17, step 4

35. Bound Neurotransmitter
Graded potential e
Binding of neurotransmitter to Receptors:
Graded Potential produced: f
Figure 11.17, step 5

36. g Neurotransmitter effects terminated: by Reuptake
Enzymatic degradation
Diffusion away from synapse g
Neurotransmitter effects terminated: by
Figure 11.17, step 6

37. Example: DRUGS THAT BLOCK RE-UPTAKE OF NEUROTRANSMITTER–Antidepressants & other drugs that block re-uptake of Serotonin, Norepinephrine, and Dopamine

38. 4. Types of Neurotransmitter-Receptor Systems
= specific neurotransmitters and the:
Body Location of & functions of Cells responsive to specific neurotransmitters
# of Different Receptors on Neurons per Neurotransmitter:
# of Different Neurotransmitters per Neuron

39. d. Neurotransmitter Classification based on Chemical Structure
Acetylcholine
Amino Acid based:
iii) Purines (nucleic acid bases):
iv) Lipid-derived:

40. 4. Mechanisms for Neurotransmitters Action
Ion Channel-linked receptors
- Direct action:
Ion flow blocked
Ions flow
Ligand
Closed ion channel
Open ion channel
(a) Channel-linked receptors open in response to binding
of ligand (ACh in this case).

41. b. G Protein-Linked Receptors Indirect action:
Eventually Channel Activates:
Neurotransmitter
(1st messenger) binds
and activates receptor. 1
Closed ion
channel
Open ion
channel
Adenylate cyclase
Receptor
G protein
cAMP changes
membrane permeability
by opening or closing ion
channels. 5a
cAMP activates
specific genes. 5c
GDP 5b
cAMP activates
enzymes.
Receptor
activates G
protein. 2
G protein
activates
adenylate
cyclase. 3
Adenylate
cyclase converts
ATP to cAMP
(2nd messenger). 4
Nucleus
Active enzyme
(b) G-protein linked receptors cause formation of an intracellular second messenger (cyclic
AMP in this case) that brings about the cell’s response.

42. END