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Neuro I

Neuro I. Or: What makes me do that Voodoo that I Do so Well!. Neurons and More Neurons. The root of it all…. The Brain. Responsible for all behavior Sensation Sensory (Afferent) Neurons Movement Motor (Efferent) Neurons Integration of info Interneurons. The Brain. Donald Hebb

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Neuro I

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  1. Neuro I Or: What makes me do that Voodoo that I Do so Well!

  2. Neurons and More Neurons The root of it all…...

  3. The Brain • Responsible for all behavior • Sensation • Sensory (Afferent) Neurons • Movement • Motor (Efferent) Neurons • Integration of info • Interneurons

  4. The Brain • Donald Hebb • Proposed that the brain is not merely a mass of tissue • but a highly integrated series of structures that perform specific functions • cell assemblies

  5. Cell Assemblies • Groups of connected neurons that perform certain functions

  6. Cell Assemblies: The Neuron • A specialized cell that receives, processes and/or transmits information • Modulatory Characteristics

  7. Depolarize Make a neighbor more likely to be active Hyperpolarize Make a neighbor less likely to fire Change the dynamics of a receptor Make it less receptive to a signal (NT) Affect synthesis, movement and release of NT to another neuron Moduation Modulatory Characteristics

  8. Neuronal Structure Spinal Motor Neuron

  9. Variations on a Theme Basket Cell (Cerebellum) Golgi Type II (Cortex)

  10. Sensory Neurons Unipolar (Pain/Touch) Bipolar (Vision)

  11. Neuronal Structure Spinal Motor Neuron

  12. Soma • Contains the nucleus and machinery • Life Processes

  13. Neuronal Structure: Dendrites Spinal Motor Neuron

  14. Dendrites (Tree) • Highly Aborized • Receive “messages” from other neurons • Some have dendritic “spines” • Input sites • Separated from neighbor by a synapse (space) • Caveat: They can transmit signals as well

  15. Dendritic Spines

  16. Neuronal Structure: Axon Spinal Motor Neuron

  17. The Axon • Tube-like structure • Micrometers to meters • Covered by the “Myelin Sheath” Axon

  18. The Axon • Tube-like structure • Carries a signal from the soma to the terminal buttons • Signal = Action Potential (AP) (electrical/chemical event) Axon

  19. Myelin Sheath

  20. Myelin Sheath • Surrounds many (but not all) axons • Formed by Oligodendrocytes (CNS) and Schwann Cells (PNS) • There are gaps between adjacent cells • Several micrometers • Called “Nodes of Ranvier” • Internode region

  21. Neuronal Structure: Terminal Buttons Spinal Motor Neuron

  22. Terminal Buttons • Found at the end of the axon • When an AP reaches the terminal • Release chemical into the synapse • Neurotransmitter (NT)

  23. Neurotransmitters • This Info can be excitatory or inhibitory to a neighboring neuron

  24. Cell Assemblies

  25. Signaling in the Neuron

  26. Electrical Potentials • Most work done with the Giant Squid Axon • Neurons work by electrical and chemical activity

  27. Electrical Potential • Inside is more negative than the outside • -70 mv • Membrane resting potential

  28. Ions • Molecules that have given up or taken on an electron • Gives the molecule a charge • Some move more readily across the membrane then others • Dependent on circumstances

  29. Ion Distribution

  30. ION INSIDE OUTSIDE RATIO K+ 400 10 40:1 Na++ 50 460 1:9 Cl- 40 540 1:13 A- 400 ------ ------ Ca++ 0.4 10 1:25 Ion Concentrations The number is not as important as the ratio

  31. Ion Concentration • More positive charge on the outside then on the inside of the neuron

  32. The Active Neuron

  33. The Action Potential (AP) • Its hard to know what’s going on • Difficult to isolate ions • Everything is occurring at once • The charge is changing • Impacts ion movement

  34. Reaching Threshold • Excitatory Input (Depolarization) • Causes the influx of positive ions (Na+) into the cell by opening Na+ channels • Voltage gated channels • Great variety in threshold level • If enough positive charge comes in • The threshold is reached • More NA+ channels open • Making the cell more positive • All or none

  35. Caveat • Takes many excitatory inputs to reach thresholds • Temporal summation • Spatial summation

  36. Repolarization • After time • The Na+ channels automatically close • K+ channels begin to open • K+ leaves the cell carrying with it the positive charge • Repolarization

  37. Overshoot • Too much K+ leaves causing the cell to be hyperpolarized

  38. Back to Resting State • The Na+/K+ pump restores the normal ion concentrations and distributions

  39. Axonal Conduction • This measurement takes place at one point on the giant squid axon • The signal must travel distances to reach its destination

  40. Signal Decrement Weak depolarization = loss of signal

  41. AP Propagation Strong depolarization = strong signal

  42. Neuronal Structure AXON HILLOCK Spinal Motor Neuron

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