Bioelectricity& Excitable Tissue
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Bioelectricity& Excitable Tissue

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Bioelectricity& Excitable Tissue Bioelectricity& Excitable Tissue Presentation Transcript

  • BIOELECTRICITY AND EXCITABLE TISSUE THE ORIGIN OF BIOELECTRICITY AND HOW NERVES WORK www.freelivedoctor.com
  • THE RESTING CELL
    • HIGH POTASSIUM
    • LOW SODIUM
    • NA/K ATPASE PUMP
    • RESTING POTENTIAL ABOUT 90 - 120 MV
    • OSMOTICALLY BALANCED (CONSTANT VOLUME)
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  • BIOELECTRICITY THE ORIGIN OF THE MEMBRANE POTENTIAL www.freelivedoctor.com
  • MOBILITY OF IONS DEPENDS ON HYDRATED SIZE
    • IONS WITH SMALLER CRYSTAL RADIUS HAVE A HIGHER CHARGE DENSITY
    • THE HIGHER CHARGE DENSITY ATTRACTS MORE WATER OF HYDRATION
    • THUS THE SMALLER THE CRYSTAL RADIUS, THE LOWER THE MOBILITY IN WATER
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  • IONS MOVE WITH THEIR HYDRATION SHELLS - + - + Hydration Shells - + - + - + - + - + - + - + - + - + www.freelivedoctor.com Na + - + - + Cl - - + - + - + - + - + - + - + - + - + - + - + - + - +
  • ELECTRONEUTRAL DIFFUSSION HIGH SALT CONCEMTRATION LOW SALT CONCEMTRATION BARRIER SEPARATES THE TWO SOLUTIONS www.freelivedoctor.com + - + - + - + - + - + - + - + -
  • ELECTRONEUTRAL DIFFUSSION + - CHARGE SEPARATION = ELECTRICAL POTENTIAL www.freelivedoctor.com HIGH SALT CONCEMTRATION LOW SALT CONCEMTRATION + - BARRIER REMOVED + - + - + - + - + - + - + -
  • 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
  • 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
  • THE ORIGIN OF BIOELECTRICITY
    • POTASSIUM CHANNELS ALLOW HIGH MOBILITY
    • SODIUM CHANNELS LESS OPEN
    • CHARGE SEPARATION OCCURS UNTIL BOTH MOVE AT SAME SPEED
    • STEADY STEADY IS ACHIEVED WITH A CONSTANT MEMBRANE POTENTIAL
    www.freelivedoctor.com
  • THE RESTING CELL
    • HIGH POTASSIUM
    • LOW SODIUM
    • NA/K ATPASE PUMP
    • RESTING POTENTIAL ABOUT 90 - 120 MV
    • OSMOTICALLY BALANCED (CONSTANT VOLUME)
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  • ACTIVE TRANSPORT ADP ATP www.freelivedoctor.com
  • ACTIVE TRANSPORT REQUIRES AN INPUT OF ENERGY
    • USUALLY IN THE FORM OF ATP
    • ATPase IS INVOLVED
    • SOME ASYMMETRY IS NECESSARY
    • CAN PUMP UPHILL
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  • EXCITABLE TISSUES
    • NERVE AND MUSCLE
    • VOLTAGE GATED CHANNELS
    • DEPOLARIZATION LESS THAN THRESHOLD IS GRADED
    • DEPOLARIZATION BEYOND THRESHOLD LEADS TO ACTION POTENTIAL
    • ACTION POTENTIAL IS ALL OR NONE
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  • THE NERVE CELL CELL BODY DENDRITES AXON AXON HILLOCK AXON TERMINALS www.freelivedoctor.com
  • EXCITABLE TISSUES:THE ACTION POTENTIAL
    • THE MEMBRANE USES VOLTAGE GATED CHANNELS TO SWITCH FROM A POTASSIUM DOMINATED TO A SODIUM DOMINATED POTENTIAL
    • IT THEN INACTIVATES AND RETURNS TO THE RESTING STATE
    • THE RESPONSE IS “ALL OR NONE”
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  • 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
  • THE EQUILIBRIUM MEMBRANE POTENTIAL FOR POTASSIUM IS -90 mV + - CONCENTRATION POTENTIAL K + K + IN www.freelivedoctor.com
  • THE EQUILIBRIUM MEMBRANE POTENTIAL FOR SODIUM IS + 60 mV Na + Na + + - CONCENTRATION POTENTIAL IN OUT www.freelivedoctor.com
  • THE RESTING POTENTIAL IS NEAR THE POTASSIUM EQUILIBRIUM POTENTIAL
    • AT REST THE POTASSIUM CHANNELS ARE MORE OPEN AND THE POTASSIUM IONS MAKE THE INSIDE OF THE CELL NEGATIVE
    • THE SODIUM CHANNELS ARE MORE CLOSED AND THE SODIUM MOVES SLOWER
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  • EVENTS DURING EXCITATION
    • DEPOLARIZATION EXCEEDS THRESHOLD
    • SODIUM CHANNELS OPEN
    • MEMBRANE POTENTIAL SHIFTS FROM POTASSIUM CONTROLLED (-90 MV) TO SODIUM CONTROLLED (+60 MV)
    • AS MEMBRANE POTENTIAL REACHES THE SODIUM POTENTIAL, THE SODIUM CHANNELS CLOSE AND ARE INACTIVATED
    • POTASSIUM CHANNELS OPEN TO REPOLARIZE THE MEMBRANE
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  • OPENING THE SODIUM CHANNELS ALLOWS SODIUM TO RUSH IN
    • THE MEMBRANE DEPOLARIZES AND THEN THE MEMBRANE POTENTIAL APPROACHES THE SODIUM EQUILIBRIUM POTENTIAL
    • THIS RADICAL CHANGE IN MEMBRANE POTENTIAL CAUSES THE SODIUM CHANNELS TO CLOSE (INACTIVATION) AND THE POTASSIUM CHANNELS TO OPEN REPOLARIZING THE MEMBRANE
    • THERE IS A SLIGHT OVERSHOOT (HYPERPOLARIZATION) DUE TO THE POTASSIUM CHANNELS BEING MORE OPEN
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  • GRADED VS ALL OR NONE
    • A RECEPTOR’S RESPONSE TO A STIMULUS IS GRADED
    • IF THRESHOLD IS EXCEEDED, THE ACTION POTENTIAL RESULTING IS ALL OR NONE
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  • PROPAGATION OF THE ACTION POTENTIAL +++++ -------- --------------------- +++++++++++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT www.freelivedoctor.com
  • PROPAGATION OF THE ACTION POTENTIAL +++++ -------- --------------------- +++++++++++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT www.freelivedoctor.com
  • PROPAGATION OF THE ACTION POTENTIAL --+++ ++------ +++------------------ ---++++++++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT www.freelivedoctor.com
  • PROPAGATION OF THE ACTION POTENTIAL -------- +++++ ++++++------- -----------++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT www.freelivedoctor.com
  • SALTATORY CONDUCTION +++++ -------- -------- +++++ AXON MEMBRANE INSIDE OUTSIDE ACTION POTENTIAL DEPOLARIZING CURRENT MYELIN NODE OF RANVIER NODE OF RANVIER www.freelivedoctor.com
  • NORMALLY A NERVE IS EXCITED BY A SYNAPSE OR BY A RECEPTOR
    • MANY NERVES SYNAPSE ON ANY GIVEN NERVE
    • RECEPTORS HAVE GENERATOR POTENTIALS WHICH ARE GRADED
    • IN EITHER CASE WHEN THE NERVE IS DEPOLARIZED BEYOND THRESHOLD IT FIRE AN ALL-OR-NONE ACTION POTENTIAL AT THE FIRST NODE OF RANVIER
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  • THE SYNAPSE
    • JUNCTION BETWEEN TWO NEURONS
    • CHEMICAL TRANSMITTER
    • MAY BE 100,000 ON A SINGLE CNS NEURON
    • SPATIAL AND TEMPORAL SUMMATION
    • CAN BE EXCITATORY OR INHIBITORY
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  • THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• INCOMING ACTION POTENTIAL CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  • THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• INCOMING ACTION POTENTIAL CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  • THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• INCOMING ACTION POTENTIAL CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  • THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  • THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME ••• www.freelivedoctor.com
  • THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  • THE SYNAPSE SYNAPTIC VESSICLES ••• ••• ••• ••• ••• ••• ••• ••• ••• CALCIUM CHANNEL ION CHANNEL RECEPTOR ENZYME www.freelivedoctor.com
  • POSTSYNAPTIC POTENTIALS RESTING POTENTIAL EPSP TIME www.freelivedoctor.com IPSP
  • TEMPORAL SUMMATION TIME TOO FAR APART IN TIME: NO SUMMATION www.freelivedoctor.com
  • TEMPORAL SUMMATION TIME CLOSER IN TIME: SUMMATION BUT BELOW THRESHOLD THRESHOLD www.freelivedoctor.com
  • TEMPORAL SUMMATION TIME STILL CLOSER IN TIME: ABOVE THRESHOLD THRESHOLD www.freelivedoctor.com
  • SPATIAL SUMMATION TIME SIMULTANEOUS INPUT FROM TWO SYNAPSES: ABOVE THRESHOLD THRESHOLD www.freelivedoctor.com
  • EPSP-IPSP CANCELLATION www.freelivedoctor.com
  • NEURO TRANSMITTERS
    • ACETYL CHOLINE
    • DOPAMINE
    • NOREPINEPHRINE
    • EPINEPHRINE
    • SEROTONIN
    • HISTAMINE
    • GLYCINE
    • GLUTAMINE
    • GAMMA-AMINOBUTYRIC ACID (GABA)
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