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Chapter 8

Chapter 8. Neurons: Cellular and Network Properties. 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

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Chapter 8

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  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

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

  11. 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+

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

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

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

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

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

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

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

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

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

  32. 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

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

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

  35. 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

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

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

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

  39. Neurocrines • Neurotransmitters • Neuromodulators • Neurohormones

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

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

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

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

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

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

  46. 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

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

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

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

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