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Descartes View

Descartes View. K&W 4-1. Luigi Galvani (1737-1798). Electrified Frogs. Luigi Galvani Frog legs attached to wire in market Electrical storm made legs move Early idea of electrical properties of nervous system. Electrical Stimulation. K&W 4-2. Neural Communication.

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Descartes View

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  1. Descartes View K&W 4-1

  2. Luigi Galvani (1737-1798)

  3. Electrified Frogs • Luigi Galvani • Frog legs attached to wire in market • Electrical storm made legs move • Early idea of electrical properties of nervous system

  4. Electrical Stimulation K&W 4-2

  5. Neural Communication

  6. The journey of nerve message As message passes along the nerve, Electrode indicates a shift from negative to positive and then back to negative again K&W 4-4

  7. Cell body end of axon Direction of neural impulse: toward axon terminals Neural Communication

  8. Hodgkin and Huxley Two Cambridge profs and a squid get together (1939)

  9. Squid and axon K&W 4-5

  10. Microelectrodes KW 4-7

  11. Recording from an axon K&W 4-6

  12. Reversal of charges K&W 4-15

  13. Ions

  14. Ions on the move Concentration gradient: move from area of higher concentration to area of lower concentration K&W 4-8

  15. Ions meet a barrier No pores = No movement of ions With pores, ions can move. Charge develops Electrical Gradient: opposite charges attract (+ --) like charges repel (+ +) K&W 4-9

  16. Ions of the axon KW 4-10

  17. Resting Cell Recording KW 4-10

  18. Resting Cell Charges KW 4-10

  19. Depolarization A Graded Potential KW 4-11

  20. Hyperpolarization KW 4-11 A Graded Potential

  21. Axons get polarized K&W 4-11

  22. When an action potential occurs, Na+ and K+ work together KW 4-13

  23. Fig. 2-17, p. 43

  24. Phases of the action potential K&W 4-14

  25. Fig. 2-15, p. 39

  26. Neural Communication

  27. Cell body end of axon Direction of neural impulse: toward axon terminals Reversal of Charges

  28. Falling dominos K&W p. 131

  29. Ion flow K&W 4-15

  30. Properties of Action Potentials • All or none: fires completely or not at all • Self-propagates: recreates itself • Does not degrade: doesn’t lose power • Full strength to the end of axon • Axon can be any length

  31. Analogies for Action Potentials • Band of Fire moving down tube • Ring sliding down a string • Doing “the wave” in stadium

  32. End of segment one

  33. Naked Neurons • Neurons without myelin sheath • Slower • Shorter • Can’t carry messages long distances • What does myelin sheath provide?

  34. Louis-Antoine Ranvier • French physician discoverer of the myelin sheath. • 1835-1922 • In 1878 he discovered myelin and the famous nodes which received his name

  35. Nodes of Ranvier K&W 4-16

  36. Saltatory conduction K&W 4-17

  37. Multiple Sclerosis • Jacqueline Du Pre • 1945-1987 • MS diagnosis in 1971 • Hilary and Jackie (1998 movie)

  38. Neuronal Integration • To fire or not to fire, that is the question • All or none principle: all or nothing at all • Why important?

  39. Firing Line

  40. Threshold

  41. Sherrington • Sir Charles Scott Sherrington • (1857-1952) • Withdrawal reflex • Principle of summation • Nobel prize in medicine 1932

  42. Withdrawal Reflex in Dogs • One mild pinch between toes  no response • Two pinches quickly in same spot  withdraw paw • Temporal Summation • Temporal = over time

  43. Paw reflex: part 2 • One mild pinch in one location  no response • Two pinches in different locations  withdraw paw • Spatial Summation • Spatial = over space

  44. Temporal: one location Postsynaptic cell Excitatory Postsynaptic Potential Presynaptic cell KW 4-19 synapse

  45. Temporal EPSP KW 4-19 top

  46. Spatial: more than one location K&W 4-20

  47. Spatial EPSP KW 4-19

  48. Importance of EPSP • Excite cells • Bring about activity • Sensation felt • Muscle moved

  49. Excitation must be balanced • Nervous system can’t run on just excitation • Sometimes better not to respond • Role on inhibition • Calm down the nervous system

  50. Role of Inhibition • Provides break for the nervous system • Lowers activity levels • Keeps the brain from over-excitation, as in epilepsy

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