12 electrochemical impulse-2010 update stacy-handout


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12 electrochemical impulse-2010 update stacy-handout

  1. 1. Important Terms <ul><li>Membrane potential – the cell membrane is </li></ul><ul><li>more negatively charged on one side than </li></ul><ul><li>the other. </li></ul><ul><li>Resting potential – when a neuron is not transmitting an electrical signal. (-70mV) </li></ul><ul><li>Microelectrodes are used to measure the resting potential. </li></ul>
  2. 2. Sodium-Potassium Pump <ul><li>Inside cell there is a lot of potassium </li></ul><ul><li>Outside of cell there is a lot of sodium. </li></ul><ul><li>The cell is more permeable to potassium, suggesting there are more potassium channels </li></ul>
  3. 3. Negative ions <ul><li>Large organic molecules, such as proteins. </li></ul><ul><li>Don’t move across the membrane easily. </li></ul>
  4. 4. Action Potential <ul><li>polarized membrane – positive exterior, negative interior </li></ul><ul><ul><li>maintained by potassium-sodium pump </li></ul></ul><ul><li>depolarization – negative exterior, positive interior </li></ul><ul><ul><li>voltage-dependent channels open to allow sodium ions to rush into the cell </li></ul></ul><ul><li>repolarization – positive exterior, negative interior </li></ul><ul><ul><li>restored by potassium-sodium pump </li></ul></ul>
  5. 5. Summarize <ul><li>Summarize the steps of how an action potential propagates in your own words. </li></ul>
  6. 6. Action Potential
  7. 7. Action Potential <ul><li>Two states of the neurons: </li></ul><ul><li>resting potential: -70mV </li></ul><ul><ul><li>required before a signal can be detected </li></ul></ul><ul><li>action potential: +40mV </li></ul><ul><ul><li>change that occurs to transmit signal </li></ul></ul>
  8. 8. Action Potential Factors <ul><li>refractory period </li></ul><ul><li>threshold </li></ul><ul><li>axon diameter </li></ul><ul><li>saltatory conduction </li></ul>
  9. 9. Refractory Period <ul><ul><li>Time is required to re-establish the resting potential after an action potential as been initiated. </li></ul></ul><ul><ul><li>no other action potential may be initiated, no matter how strong the signal </li></ul></ul>
  10. 10. Refractory Period
  11. 11. Threshold Level <ul><li>Different neurons have differing threshold levels before an action potential will proceed. </li></ul><ul><li>Sensitive neurons will have low threshold values. </li></ul><ul><li>all-or-none response – neurons will or will not fire </li></ul>
  12. 12. Threshold Level
  13. 13. Axon Diameter <ul><li>greater axon diameter = greater axon surface area </li></ul><ul><li>Larger surface area has more ion channels and therefore less time to depolarize and repolarize. </li></ul><ul><ul><li>faster signals </li></ul></ul>
  14. 14. Saltatory Conduction <ul><li>Na + and K + exchange can only occur where the axons are exposed to the extracellular fluid. </li></ul><ul><li>allows for faster signal conduction along the axon </li></ul>
  15. 15. Synapse <ul><li>synapse – structure formed by two adjacent neurons </li></ul><ul><li>action potentials cause axon terminals to release neurotransmitters into the synaptic cleft </li></ul>
  16. 16. Neurotransmitters <ul><li>acetylcholine – common neurotransmitter </li></ul><ul><li>released upon neuron depolarization </li></ul><ul><ul><li>from presynaptic neuron </li></ul></ul><ul><li>causes Na + channels to be opened </li></ul><ul><li>Animation </li></ul>
  17. 17. Neurotransmitters <ul><li>How does the postsynaptic neuron know when the signal has stopped? </li></ul><ul><li>enzymes released will degrade the chemical </li></ul><ul><ul><li>cholinesterase – released by postsynaptic neuron </li></ul></ul>
  18. 18. Signals <ul><li>positive </li></ul><ul><ul><li>causes action potential to proceed in postsynaptic cell </li></ul></ul><ul><li>negative </li></ul><ul><ul><li>prevents action potential to proceed </li></ul></ul><ul><ul><li>hyperpolarization – membrane is more negative; therefore stronger signal needed </li></ul></ul><ul><li>positive and negative signals collect ( summation ) on postsynaptic neuron </li></ul>Putting it all Together