1. Neurons: Cellular and Network Properties
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. Figure 8-11: Ion movements during the action potential
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

51. Convergent Integration: Additive Summation
Multiple excitatory GPs
Temporal summation
Additive strength at trigger zone

52. Convergent Integration: Additive Summation
Figure 8-26a: Spatial summation

53. Convergent Integration: Inhibitory Summation
Inhibitory GPs cancel strength of excitatory GP
Signal at trigger too weak – no AP produced
Figure 8-26b: Spatial summation

54. Nervous Tissue Development
100 billion neurons find their target
Growth cones
Follow growth factors, structural proteins
Neurotropic factors – sustain new synapse
"Use it or loose it"

55. Pathologies Synaptic transmission Drugs in ECF
Disorders of ion balance
Too much/too little NT release
Examples: Parkinson's, schizophrenia, epilepsy, depression
Nerve injury
Limited regrowth
Parallel nerves help some

56. Figure 8-31: Injury to neurons
Pathologies
Figure 8-31: Injury to neurons

57. Summary
Organization and role of the nervous system: CNS & components of PNS
Neuron and glial cell structure and function
Electrical signals from waves of depolarization
Graded potentials function and mechanism
Action potentials function and mechanism

58. Summary Synapse: neurotransmitters, cell to cell communication
Conduction, integration and modulation of the signals
Development and pathologies of the nervous system