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 Figure 8-3: Anatomic and functional categories of neurons

7. 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

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

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

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

12. 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

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

14. 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

35. 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

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

37. 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

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

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

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

41. Neurocrines • Neurotransmitters • Neuromodulators • Neurohormones

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

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

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

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

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

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

48. 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

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

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