Chapter 8

1. Chapter 8 Neurons: Cellular and Network Properties

2. About this Chapter • How the nervous system is organized • Nerve cell types and roles • Excitability and electrical signals • Graded and action potentials initiation and conduction • Neurotransmitters and signal conduction cell to cell • Modulation and integration of the signals • Damage and diseases of the nerves

3. Organization of the Nervous System • Rapid communication for homeostatic balance • Emergent properties of intelligence & emotion • Central Nervous system (CNS) • Peripheral Nervous system (PNS)

4. Organization of the Nervous System Figure 8-1: Organization of the nervous system

5. A Typical Neuron Overview • Dendrites • Cell Body • Axon • Terminal Figure 8-2: Model neuron

6. Diverse Neuron Forms and Functions • Pseudounipolar • Bipolar • Anaxionic • Multipolar–CNS • Multipolar–efferent

7. Diverse Neuron Forms and Functions Figure 8-3: Anatomic and functional categories of neurons

8. Metabolism and Synthesis in a Neuron • Cell body site of energy generation and synthesis • Axonal transport • Vesicles – • Fast axonal transport to terminal • Retrograde to cell body • Electrical depolarizations

9. Metabolism and Synthesis in a Neuron Figure 8-4: Axonal transport of membranous organelles

11. Glial Cell Functions • Support neuron bodies, form myelin sheaths • Barriers between compartments • Scavenger/defense & metabolic assistance

12. Glial Cell Functions Figure 8-5: Glial cells and their functions

13. Electrical Signals: Ionic Concentrations and Potentials • Nernst & GHK Equations predict • Membrane potential • Cell concentration gradients • [Na+, Cl- & Ca2+] higher in ECF • [K+] higher ICF • Depolarization causes electrical signal • Gated channels control permeability

14. Electrical Signals: Ionic Concentrations and Potentials Table 8-2: Ion Concentrations and Equilibrium Potentials

15. Graded Potentials • Incoming signals • Vary in strength • Lose strength over distance • Are slower than action potentials (AP) • Travels to trigger zone • Subthreshold – • Too weak • No generation of AP • Suprathreshold – generate AP

16. Graded Potentials Figure 8-7: Graded potentials decrease in strength as they spread out from the point of origin

17. Trigger Zone: Cell Integration and Initiation of AP • Excitatory signal: depolarizes, reduces threshold • Inhibitory signal: hyperpolarizes, increases threshold

18. Trigger Zone: Cell Integration and Initiation of AP Figure 8-8a: Subthreshold and suprathreshold graded potentials in a neuron

19. Trigger Zone: Cell Integration and Initiation of AP Figure 8-8b: Subthreshold and suprathreshold graded potentials in a neuron

20. Action Potential Stages: Overview • "All or none" • Signal does not diminish over distance

21. Action Potential Stages: Overview Figure 8-9: The action potential

22. Membrane & Channel Changes during an Action Potential • Initiation • Depolarization • Signal peak • Repolarization

23. Membrane & Channel Changes during an Action Potential Figure 8-10: Model of the voltage-gated channel Na+

24. Regulating the AP • Positive feedback loop • Absolute refractory period • Relative refractory period

25. Regulating the AP Figure 8-11: Ion movements during the action potential

26. Regulating the AP Figure 8-12: Refractory periods

27. Frequency of Action Potentials • Firing rate • "Wave" of APs • Proportional neurotransmitter (NT) release • Stronger GP initiates more APs & more NT

28. Frequency of Action Potentials Figure 8-13: Coding for stimulus intensity

29. Conduction of Action Potentials • Kinetic energy • Depolarizes ahead • Drives AP to terminal

30. Conduction of Action Potentials Figure 8-14a: Conduction of action potentials

31. Conduction of Action Potentials Figure 8-14b: Conduction of action potentials

32. Conduction of Action Potentials Figure 8-14c: Conduction of action potentials

33. Speed of Conduction • Larger diameter faster conduction • Myelinated axon faster conduction • Saltatory conduction • Disease damage to myelin • Chemicals that block channels • Alteration of ECF ion concentrations

34. Speed of Conduction Figure 8-16b: Axon diameter and speed of conduction

35. Speed of Conduction Figure 8-17: Saltatory conduction

36. Cell to Cell Conduction: the Synapse • Electrical synapses: gap junctions • Very fast conduction • Example: cardiac muscle • Chemical synapses • Pre synaptic terminal • Synthesis of Neurotransmitters • Ca2+ releases Neurotransmitters • Synaptic cleft • Postsynaptic cell: Neurotransmitter receptors

37. Cell to Cell Conduction: the Synapse Figure 8-19: A chemical synapse

38. Synapse Mechanism Figure 8-20: Events at the synapse

39. Acetylcholine synthesis Figure 8-21: Synthesis and recycling of acetylcholine at the synapse

40. Neurocrines • Neurotransmitters • Neuromodulators • Neurohormones

41. Neurocrines Table 8-4-1: Major Neurocrines

42. Neurocrines Table 8-4-2: Major Neurocrines

43. Multiple Receptors modify signal • Amplification – depolarization • Inhibition – hyperpolarization • Duration • Fast – channel opening • Slow – protein synthesis

44. Multiple Receptors modify signal Figure 8-22: Fast and slow responses in postsynaptic cells

45. Inactivation of Neurotransmitters • Recycled • Enzyme degradation • Diffuse away

46. Inactivation of Neurotransmitters Figure 8-23: Inactivation of neurotransmitters

47. Integration of Signals • Information transfer at each exchange • Signal can be lost • Signal can be enhanced • Divergence – one cell to many • Convergence – many cells to one

48. Integration of Signals Figure 8-24a: Convergence and divergence

49. Integration of Signals Figure 8-24b: Convergence and divergence

50. Integration of Signals Figure 8-25: Locations of synapses on a postsynaptic neuron