Bioelectricity& Excitable Tissue

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Bioelectricity& Excitable Tissue

  1. 1. BIOELECTRICITY AND EXCITABLE TISSUE THE ORIGIN OF BIOELECTRICITY AND HOW NERVES WORK www.freelivedoctor.com
  2. 2. THE RESTING CELL <ul><li>HIGH POTASSIUM </li></ul><ul><li>LOW SODIUM </li></ul><ul><li>NA/K ATPASE PUMP </li></ul><ul><li>RESTING POTENTIAL ABOUT 90 - 120 MV </li></ul><ul><li>OSMOTICALLY BALANCED (CONSTANT VOLUME) </li></ul>www.freelivedoctor.com
  3. 3. www.freelivedoctor.com
  4. 4. BIOELECTRICITY THE ORIGIN OF THE MEMBRANE POTENTIAL www.freelivedoctor.com
  5. 5. MOBILITY OF IONS DEPENDS ON HYDRATED SIZE <ul><li>IONS WITH SMALLER CRYSTAL RADIUS HAVE A HIGHER CHARGE DENSITY </li></ul><ul><li>THE HIGHER CHARGE DENSITY ATTRACTS MORE WATER OF HYDRATION </li></ul><ul><li>THUS THE SMALLER THE CRYSTAL RADIUS, THE LOWER THE MOBILITY IN WATER </li></ul>www.freelivedoctor.com
  6. 6. IONS MOVE WITH THEIR HYDRATION SHELLS - + - + Hydration Shells - + - + - + - + - + - + - + - + - + www.freelivedoctor.com Na + - + - + Cl - - + - + - + - + - + - + - + - + - + - + - + - + - +
  7. 7. ELECTRONEUTRAL DIFFUSSION HIGH SALT CONCEMTRATION LOW SALT CONCEMTRATION BARRIER SEPARATES THE TWO SOLUTIONS www.freelivedoctor.com + - + - + - + - + - + - + - + -
  8. 8. ELECTRONEUTRAL DIFFUSSION + - CHARGE SEPARATION = ELECTRICAL POTENTIAL www.freelivedoctor.com HIGH SALT CONCEMTRATION LOW SALT CONCEMTRATION + - BARRIER REMOVED + - + - + - + - + - + - + -
  9. 9. ELECTRICAL POTENTIAL=CHARGE SEPARATION In water, without a membrane hydrated Chloride is smaller than hydrated Sodium, therefore faster: Cl - Na + The resulting separation of charge is called an ELECTRICAL POTENTIAL + - www.freelivedoctor.com
  10. 10. THE MEMBRANE POTENTIAL M E M B R A N E Extracellular Fluid Intracellular Fluid Na + K + Sodium channel is less open causing sodium to be slower Potassium channel is more open causing potassium to be faster + - MEMRANE POTENTIAL (ABOUT 90 -120 mv) www.freelivedoctor.com
  11. 11. THE ORIGIN OF BIOELECTRICITY <ul><li>POTASSIUM CHANNELS ALLOW HIGH MOBILITY </li></ul><ul><li>SODIUM CHANNELS LESS OPEN </li></ul><ul><li>CHARGE SEPARATION OCCURS UNTIL BOTH MOVE AT SAME SPEED </li></ul><ul><li>STEADY STEADY IS ACHIEVED WITH A CONSTANT MEMBRANE POTENTIAL </li></ul>www.freelivedoctor.com
  12. 12. THE RESTING CELL <ul><li>HIGH POTASSIUM </li></ul><ul><li>LOW SODIUM </li></ul><ul><li>NA/K ATPASE PUMP </li></ul><ul><li>RESTING POTENTIAL ABOUT 90 - 120 MV </li></ul><ul><li>OSMOTICALLY BALANCED (CONSTANT VOLUME) </li></ul>www.freelivedoctor.com
  13. 13. www.freelivedoctor.com
  14. 14. ACTIVE TRANSPORT ADP ATP www.freelivedoctor.com
  15. 15. ACTIVE TRANSPORT REQUIRES AN INPUT OF ENERGY <ul><li>USUALLY IN THE FORM OF ATP </li></ul><ul><li>ATPase IS INVOLVED </li></ul><ul><li>SOME ASYMMETRY IS NECESSARY </li></ul><ul><li>CAN PUMP UPHILL </li></ul>www.freelivedoctor.com
  16. 16. EXCITABLE TISSUES <ul><li>NERVE AND MUSCLE </li></ul><ul><li>VOLTAGE GATED CHANNELS </li></ul><ul><li>DEPOLARIZATION LESS THAN THRESHOLD IS GRADED </li></ul><ul><li>DEPOLARIZATION BEYOND THRESHOLD LEADS TO ACTION POTENTIAL </li></ul><ul><li>ACTION POTENTIAL IS ALL OR NONE </li></ul>www.freelivedoctor.com
  17. 17. THE NERVE CELL CELL BODY DENDRITES AXON AXON HILLOCK AXON TERMINALS www.freelivedoctor.com
  18. 18. EXCITABLE TISSUES:THE ACTION POTENTIAL <ul><li>THE MEMBRANE USES VOLTAGE GATED CHANNELS TO SWITCH FROM A POTASSIUM DOMINATED TO A SODIUM DOMINATED POTENTIAL </li></ul><ul><li>IT THEN INACTIVATES AND RETURNS TO THE RESTING STATE </li></ul><ul><li>THE RESPONSE IS “ALL OR NONE” </li></ul>www.freelivedoctor.com
  19. 19. EQUILIBRIUM POTENTIALS FOR IONS FOR EACH CONCENTRATION DIFFERENCE ACROSS THE MEMBRANE THERE IS AN ELECTRIC POTENTIAL DIFFERENCE WHICH WILL PRODUCE EQUILIBRIUM. AT EQUILIBRIUM NO NET ION FLOW OCCURS www.freelivedoctor.com
  20. 20. THE EQUILIBRIUM MEMBRANE POTENTIAL FOR POTASSIUM IS -90 mV + - CONCENTRATION POTENTIAL K + K + IN www.freelivedoctor.com
  21. 21. THE EQUILIBRIUM MEMBRANE POTENTIAL FOR SODIUM IS + 60 mV Na + Na + + - CONCENTRATION POTENTIAL IN OUT www.freelivedoctor.com
  22. 22. THE RESTING POTENTIAL IS NEAR THE POTASSIUM EQUILIBRIUM POTENTIAL <ul><li>AT REST THE POTASSIUM CHANNELS ARE MORE OPEN AND THE POTASSIUM IONS MAKE THE INSIDE OF THE CELL NEGATIVE </li></ul><ul><li>THE SODIUM CHANNELS ARE MORE CLOSED AND THE SODIUM MOVES SLOWER </li></ul>www.freelivedoctor.com
  23. 23. EVENTS DURING EXCITATION <ul><li>DEPOLARIZATION EXCEEDS THRESHOLD </li></ul><ul><li>SODIUM CHANNELS OPEN </li></ul><ul><li>MEMBRANE POTENTIAL SHIFTS FROM POTASSIUM CONTROLLED (-90 MV) TO SODIUM CONTROLLED (+60 MV) </li></ul><ul><li>AS MEMBRANE POTENTIAL REACHES THE SODIUM POTENTIAL, THE SODIUM CHANNELS CLOSE AND ARE INACTIVATED </li></ul><ul><li>POTASSIUM CHANNELS OPEN TO REPOLARIZE THE MEMBRANE </li></ul>www.freelivedoctor.com
  24. 24. OPENING THE SODIUM CHANNELS ALLOWS SODIUM TO RUSH IN <ul><li>THE MEMBRANE DEPOLARIZES AND THEN THE MEMBRANE POTENTIAL APPROACHES THE SODIUM EQUILIBRIUM POTENTIAL </li></ul><ul><li>THIS RADICAL CHANGE IN MEMBRANE POTENTIAL CAUSES THE SODIUM CHANNELS TO CLOSE (INACTIVATION) AND THE POTASSIUM CHANNELS TO OPEN REPOLARIZING THE MEMBRANE </li></ul><ul><li>THERE IS A SLIGHT OVERSHOOT (HYPERPOLARIZATION) DUE TO THE POTASSIUM CHANNELS BEING MORE OPEN </li></ul>www.freelivedoctor.com
  25. 25. GRADED VS ALL OR NONE <ul><li>A RECEPTOR’S RESPONSE TO A STIMULUS IS GRADED </li></ul><ul><li>IF THRESHOLD IS EXCEEDED, THE ACTION POTENTIAL RESULTING IS ALL OR NONE </li></ul>www.freelivedoctor.com
  26. 26. www.freelivedoctor.com
  27. 27. www.freelivedoctor.com
  28. 28. PROPAGATION OF THE ACTION POTENTIAL +++++ -------- --------------------- +++++++++++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT www.freelivedoctor.com
  29. 29. PROPAGATION OF THE ACTION POTENTIAL +++++ -------- --------------------- +++++++++++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT www.freelivedoctor.com
  30. 30. PROPAGATION OF THE ACTION POTENTIAL --+++ ++------ +++------------------ ---++++++++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT www.freelivedoctor.com
  31. 31. PROPAGATION OF THE ACTION POTENTIAL -------- +++++ ++++++------- -----------++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT www.freelivedoctor.com
  32. 32. SALTATORY CONDUCTION +++++ -------- -------- +++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT MYELIN NODE OF RANVIER NODE OF RANVIER www.freelivedoctor.com
  33. 33. NORMALLY A NERVE IS EXCITED BY A SYNAPSE OR BY A RECEPTOR <ul><li>MANY NERVES SYNAPSE ON ANY GIVEN NERVE </li></ul><ul><li>RECEPTORS HAVE GENERATOR POTENTIALS WHICH ARE GRADED </li></ul><ul><li>IN EITHER CASE WHEN THE NERVE IS DEPOLARIZED BEYOND THRESHOLD IT FIRE AN ALL-OR-NONE ACTION POTENTIAL AT THE FIRST NODE OF RANVIER </li></ul>www.freelivedoctor.com
  34. 34. www.freelivedoctor.com
  35. 35. THE SYNAPSE <ul><li>JUNCTION BETWEEN TWO NEURONS </li></ul><ul><li>CHEMICAL TRANSMITTER </li></ul><ul><li>MAY BE 100,000 ON A SINGLE CNS NEURON </li></ul><ul><li>SPATIAL AND TEMPORAL SUMMATION </li></ul><ul><li>CAN BE EXCITATORY OR INHIBITORY </li></ul>www.freelivedoctor.com
  36. 36. THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• INCOMING ACTION POTENTIAL CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  37. 37. THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• INCOMING ACTION POTENTIAL CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  38. 38. THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• INCOMING ACTION POTENTIAL CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  39. 39. THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  40. 40. THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME ••• www.freelivedoctor.com
  41. 41. THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  42. 42. THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  43. 43. POSTSYNAPTIC POTENTIALS RESTING POTENTIAL EPSP TIME www.freelivedoctor.com IPSP
  44. 44. TEMPORAL SUMMATION TIME TOO FAR APART IN TIME: NO SUMMATION www.freelivedoctor.com
  45. 45. TEMPORAL SUMMATION TIME CLOSER IN TIME: SUMMATION BUT BELOW THRESHOLD THRESHOLD www.freelivedoctor.com
  46. 46. TEMPORAL SUMMATION TIME STILL CLOSER IN TIME: ABOVE THRESHOLD THRESHOLD www.freelivedoctor.com
  47. 47. SPATIAL SUMMATION TIME SIMULTANEOUS INPUT FROM TWO SYNAPSES: ABOVE THRESHOLD THRESHOLD www.freelivedoctor.com
  48. 48. EPSP-IPSP CANCELLATION www.freelivedoctor.com
  49. 49. NEURO TRANSMITTERS <ul><li>ACETYL CHOLINE </li></ul><ul><li>DOPAMINE </li></ul><ul><li>NOREPINEPHRINE </li></ul><ul><li>EPINEPHRINE </li></ul><ul><li>SEROTONIN </li></ul><ul><li>HISTAMINE </li></ul><ul><li>GLYCINE </li></ul><ul><li>GLUTAMINE </li></ul><ul><li>GAMMA-AMINOBUTYRIC ACID (GABA) </li></ul>www.freelivedoctor.com

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