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Neurons: Anatomy & Physiology

Neurons: Anatomy & Physiology. Review: Chapter 2 of textbook. Information from prerequisite classes, that I assume you know. Neurons. Basic functional unit of N.S. Specialized cell All cells have same basic properties information processing Transmits Integrates Stores

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Neurons: Anatomy & Physiology

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  1. Neurons: Anatomy & Physiology Review: Chapter 2 of textbook.Information from prerequisite classes, that I assume you know.

  2. Neurons • Basic functional unit of N.S. • Specialized cell • All cells have same basic properties • information processing • Transmits • Integrates • Stores • Regulation of behavior ~

  3. Stimuli • Dendrites & soma • Receive & Integrate information ~ • Axon carries information away from soma • Electrical signal • Axon terminal releases chemical message • neurotransmitter (NT) ~

  4. Neuronal Membrane • Common Cellular Properties • Compartmentalization • Semipermeable • Fluid Mosaic Model • Phospholipids • Proteins ~

  5. Hydrophilic heads Hydrophobic tails Phospholipid Bilayer

  6. Membrane Proteins: Ionophores • Ions Channels • Nongated • Gated • mechanically -gated • electrically-gated (voltage-gated) • chemically -gated ~

  7. Membrane Proteins OUTSIDE NT INSIDE

  8. Membrane is polarized • More negative particles inside than out • unequal distribution of ions • Bioelectric Potential • like a battery • Potential for ion movement • current ~

  9. Resting Membrane Potential Na+ Cl- outside + + + + + + + + + + + Membrane - - - - - - - - - - - inside A- K+

  10. Forces That Move Ions • Concentration (C) • particles in fluid move from area of high to area of low concentration • diffusion, random movement • Electrostatic (E) • ions = charged particles • like charges repel • opposite charges attract ~

  11. C Organic anions - Membrane impermeable Opposing electrical force not required Vm = -65 mV A-

  12. C E Chloride ion Cl- • ECl- = - 65 mV • Concentration gradientequal toelectrostatic gradient. • *No net movement at resting potential ~ Vm = -65 mV

  13. E C Potassium ion • EK = - 75 mV • Concentration gradientgreater thanelectrostatic gradient. • Leaks out neuron ~ Vm = -65 mV K+

  14. Na+ C E Sodium ion • ENa+ = +55 mV • Concentration gradientandelectrostatic gradient into neuron. ~ Vm = -65 mV

  15. Neural Signaling Neural Communication • Inside neuron • Electrical signal • 2 types of current • Postsynaptic potentials • dendrites & soma • Action potential (AP) • carries information down axon • triggers NT release into synapse ~

  16. Postsynaptic Potentials - PSPs • Chemically-gated ion channels • Graded • Summation • Passive current (electrotonic) • Fast • Decremental • Relatively long-lasting • 10 - 100 msec ~

  17. EPSPs • Excitatory Postsynaptic Potential • Depolarization (+) • Em becomes more positive • more likely to trigger AP • Na+ influx ~

  18. IPSPs • Inhibitory Postsynaptic Potential • similar to EPSPs • EXCEPT opposite • hyperpolarization (-) • Em becomes more negative • less likely to trigger AP • K+ efflux ~

  19. Integration • EPSPs & IPSPs summate • become stronger • or cancel each other • Net stimulation • determines message • excitation • or inhibition ~

  20. EPSP Excitatory Depolarization Na+ influx AP more likely IPSP Inhibitory Hyperpolarization K+ efflux AP less likely Postsynaptic Potentials • Soma & Dendrites • Chemically-gated channels • Passive current • Graded • Summation

  21. Action Potentials • Large and rapid change in membrane potential • Occurs in axon only • voltage-gated channels • triggered by EPSPs • at axon hillock • threshold potential ~

  22. +40 0 -60 -70 -80 Time Vm

  23. +40 Depolarization Na+ influx 0 Vm -60 -70 -80 Time

  24. +40 Repolarization K+ efflux 0 Vm -60 -70 -80 Time

  25. +40 After- hyperpolarization K+ efflux 0 Vm -60 -70 -80 Time

  26. AP Characteristics • Voltage-gated channels • All or none • Self-propagated • regenerated • Non-decremental • Slow • Short-lived change in Em • 1-2 msec ~

  27. Frequency Code • Pattern = Intensity of stimulus • # APs per second • Place = type of stimulus • Visual, auditory, pain, etc. • Brain area that receives signal ~

  28. Injected Current 0 mV -65 mV Time  Subthreshold stimulus Moderate stimulus Strong stimulus

  29. PSPs vs APs Graded All-or-none Summation chemical-gated voltage-gated longer duration short 10-100 msec 1-2 msec passive spread propagated instantaneous slow decremental nondecremental

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