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 12.2 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 C.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: b.Initiated by: c.Threshold: Membrane depolarized by 15 to 20 mV d.Myelinated and Unmyelinated (see diagram next slide) Subthreshold stimulus is not detected Dendrites Action Potential Graded Potential Neurotransmitter

3. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2010 Pearson Education, Inc. Non-Myelinated Axon Myelinated Axon

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

5. Action Potential Neurotransmitter GP 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 Dendrites Section of Membrane

6. Action potential 1 2 3 4 Resting state Depolarization Repolarization Hyperpolarization The big picture 11 2 3 4 Time (ms) Threshold Membrane potential (mV) Figure 11.11 (1 of 5) Action Potentials …

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 Na+ activation gate: closed Na+ inactivation gate open K+ activation gate: closed Na + Potassium channel Sodium channel 1 Resting state Activation gates Inactivation gate K+K+ Takes 2 milli seconds

9. Action Potentials … b. Depolarizing Phase a. Initiated by: b. At threshold: c. Na+ flows in and membrane becomes: d. End Point-- + 30mVolts: e. Restoration to Resting State: Na + 2 Depolarization K+K+

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

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

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

13. Generation of an Action Potential

14. Action potential Time (ms) 1 1 2 3 4 Na + permeability K + permeability The AP is caused by permeability changes in the plasma membrane Membrane potential (mV) Relative membrane permeability Figure 11.11 (2 of 5)

15. 5. Propagation of the Action Potential – a. Nonmyelinated Axon 1.Moves in: one direction: 2.Continuously 3.Local Current generated: Na+ that have entered the axon move horizontally towards the more negative adjacent section of the membrane: 4.Na+ Channels of adjacent section of membrane: 5. Positive Feedback Cycle:

16. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2010 Pearson Education, Inc. APs self-propagate – once started, all voltage channels open like dominoes (all or none) Voltage at 2 ms Voltage at 4 ms Voltage at 0 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. Action Potentials … Propagation of an Action Potential … b. Myelinated Axon = Saltatory Conduction 1. Location of channels: 2. AP generate at: 3. 30 times faster SHOW REST OF VIDEO

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

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

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

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. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Copyright © 2010 Pearson Education, Inc. 12.5 Communication Between Neurons A. Graded Potentials - see previous section =

27. Copyright © 2010 Pearson Education, Inc. Nerve Impulses– within and between neurons Neurotransmitters Synapse

28. A. Types of Synapses  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 1.Drug (legal & illegal) Affects–: Addiction is due to:

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

31. Figure 11.17, step 1 Action potential arrives at axon terminal. B. The Chemical Synapse … 3. Steps of Presynaptic Neuron communication with Postsynaptic Neuron Ca 2+ Synaptic vesicles Axon terminal Mitochondrion Postsynaptic neuron Presynaptic neuron Synaptic cleft Ca 2+ Postsynaptic neuron a

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

33. Figure 11.17, step 3 Ca 2+ entry causes: Ca 2+ Axon terminal Mitochondrion Postsynaptic neuron Presynaptic neuron Synaptic cleft Ca 2+ Postsynaptic neuron c The Chemical Synapse Synaptic vesicles

34. Figure 11.17, step 4 Ca 2+ Synaptic vesicles Axon terminal Mitochondrion Postsynaptic neuron Presynaptic neuron Synaptic cleft Ca 2+ Neurotransmitter: Postsynaptic neuron d The Chemical Synapse

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

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

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: a.Body Location of & functions of Cells responsive to specific neurotransmitters b.# of Different Receptors on Neurons per Neurotransmitter: c.# of Different Neurotransmitters per Neuron

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

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

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

42. END