12 electrochemical impulse


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12 electrochemical impulse

  1. 1. Action Potential Animation
  2. 2. Action Potential polarized membrane – positive exterior, negative interior  maintained by sodium-potassium pump depolarization – negative exterior, positive interior  voltage-dependent channels open to allow sodium ions to rush into the cell repolarization – positive exterior, negative interior  voltage-dependent channels open to allow potassium ions to leave the cell  restored by sodium-potassium pump
  3. 3. Action Potential Animation
  4. 4. Summarize Summarize the steps of how an action potential propagates in your own words.
  5. 5. Action Potential
  6. 6. Action Potential Two states of the neurons: 1. resting potential: -70mV  1. required before a signal can be detected action potential: +40mV  change that occurs to transmit signal
  7. 7. Action Potential Factors 1. refractory period 2. threshold 3. axon diameter 4. saltatory conduction
  8. 8. Refractory Period Time is required to re-establish the resting potential after an action potential has been initiated.  no other action potential may be initiated, no matter how strong the signal
  9. 9. Refractory Period
  10. 10. Threshold Level Different neurons have differing threshold levels before an action potential will proceed. Sensitive neurons will have low threshold values. all-or-none response – neurons will or will not fire
  11. 11. Threshold Level
  12. 12. Axon Diameter greater axon diameter = greater axon surface area Larger surface area results in more ion channels and therefore less time to depolarize and repolarize. faster signals
  13. 13. Saltatory Conduction Na+ and K+ exchange can only occur where the axons are exposed to the extracellular fluid. allows for faster signal conduction along the axon
  14. 14. presynaptic neurons postsynaptic neurons
  15. 15. Synapse synapse – structure formed by two adjacent neurons action potentials cause axon terminals to release neurotransmitters into the synaptic cleft
  16. 16. Types of Na+ Channels 1. chemical-dependent  postsynaptic cells receive chemical signals 1. electrical-dependent  ion channels opened due to membrane depolarization
  17. 17. Neurotransmitters acetylcholine – common neurotransmitter released upon neuron depolarization from presynaptic neuron causes Na+ channels to be opened in the postsynaptic neuron Animation
  18. 18. Neurotransmitters How does the postsynaptic neuron know when the signal has stopped? enzymes released will degrade the chemical cholinesterase – released by postsynaptic neuron
  19. 19. Signals 1. positive  causes action potential to proceed in postsynaptic cell 2. negative  prevents action potential to proceed  hyperpolarization – membrane is more negative; therefore stronger signal needed
  20. 20. Threshold Level
  21. 21. Putting it all Together positive and negative signals collect (summation) on postsynaptic neuron Why are negative signals important? experience has told you what should be concentrated on and what can be ignored