BIOELECTRICITY AND EXCITABLE TISSUETHE ORIGIN OF BIOELECTRICITY AND HOW NERVES WORKD. C. Mikulecky Department of Physiology andFaculty Mentoring Program

THE RESTING CELLHIGH POTASSIUMLOW SODIUMNA/K ATPASE PUMP RESTING POTENTIAL ABOUT 90 - 120 MVOSMOTICALLY BALANCED (CONSTANT VOLUME)

BIOELECTRICITYTHE ORIGIN OF THE MEMBRANE POTENTIAL

MOBILITY OF IONS DEPENDS ON HYDRATED SIZEIONS WITH SMALLER CRYSTAL RADIUS HAVE A HIGHER CHARGE DENSITYTHE HIGHER CHARGE DENSITY ATTRACTS MORE WATER OF HYDRATIONTHUS THE SMALLER THE CRYSTAL RADIUS, THE LOWER THE MOBILITY IN WATER

IONS MOVE WITH THEIR HYDRATION SHELLS- +- +Hydration Shells- +- +- +- +- +- +- +- +- +

ELECTRONEUTRAL DIFFUSSIONHIGH SALT CONCEMTRATIONLOW SALT CONCEMTRATIONBARRIER SEPARATES THE TWO SOLUTIONS

ELECTRONEUTRAL DIFFUSSION+-CHARGE SEPARATION = ELECTRICAL POTENTIAL

ELECTRICAL POTENTIAL=CHARGE SEPARATIONIn 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

+-

THE MEMBRANE POTENTIALMEMBRANEExtracellularFluidIntracellularFluidNa+K+Sodium channel is less open causing sodium to be slowerPotassium channel is more open causing potassium to be faster+-MEMRANE POTENTIAL(ABOUT 90 -120 mv)

THE ORIGIN OF BIOELECTRICITYPOTASSIUM CHANNELS ALLOW HIGH MOBILITYSODIUM CHANNELS LESS OPENCHARGE SEPARATION OCCURS UNTIL BOTH MOVE AT SAME SPEED STEADY STEADY IS ACHIEVED WITH A CONSTANT MEMBRANE POTENTIAL

THE RESTING CELLHIGH POTASSIUMLOW SODIUMNA/K ATPASE PUMP RESTING POTENTIAL ABOUT 90 - 120 MVOSMOTICALLY BALANCED (CONSTANT VOLUME)

ACTIVE TRANSPORTADP ATP

ACTIVE TRANSPORT REQUIRES AN INPUT OF ENERGYUSUALLY IN THE FORM OF ATPATPase IS INVOLVEDSOME ASYMMETRY IS NECESSARYCAN PUMP UPHILL

EXCITABLE TISSUESNERVE AND MUSCLEVOLTAGE GATED CHANNELSDEPOLARIZATION LESS THAN THRESHOLD IS GRADEDDEPOLARIZATION BEYOND THRESHOLD LEADS TO ACTION POTENTIALACTION POTENTIAL IS ALL OR NONE

THE NERVE CELLCELLBODYDENDRITESAXONAXONHILLOCKAXONTERMINALS

EXCITABLE TISSUES:THE ACTION POTENTIALTHE MEMBRANE USES VOLTAGE GATED CHANNELS TO SWITCH FROM A POTASSIUM DOMINATED TO A SODIUM DOMINATED POTENTIALIT THEN INACTIVATES AND RETURNS TO THE RESTING STATETHE RESPONSE IS ALL OR NONE

FOR EACH CONCENTRATION DIFFERENCE ACROSS THE MEMBRANE THERE IS AN ELECTRIC POTENTIAL DIFFERENCE WHICH WILL PRODUCE EQUILIBRIUM.

AT EQUILIBRIUM NO NET ION FLOW OCCURSEQUILIBRIUM POTENTIALS FOR IONS

THE EQUILIBRIUM MEMBRANE POTENTIAL FOR POTASSIUM IS -90 mV+-CONCENTRATIONPOTENTIALK+K+IN

THE EQUILIBRIUM MEMBRANE POTENTIAL FOR SODIUM IS + 60 mVNa+Na++-CONCENTRATIONPOTENTIALINOUT

THE RESTING POTENTIAL IS NEAR THE POTASSIUM EQUILIBRIUM POTENTIALAT REST THE POTASSIUM CHANNELS ARE MORE OPEN AND THE POTASSIUM IONS MAKE THE INSIDE OF THE CELL NEGATIVETHE SODIUM CHANNELS ARE MORE CLOSED AND THE SODIUM MOVES SLOWER

EVENTS DURING EXCITATION DEPOLARIZATION EXCEEDS THRESHOLDSODIUM CHANNELS OPENMEMBRANE 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 INACTIVATEDPOTASSIUM CHANNELS OPEN TO REPOLARIZE THE MEMBRANE

OPENING THE SODIUM CHANNELS ALLOWS SODIUM TO RUSH INTHE MEMBRANE DEPOLARIZES AND THEN THE MEMBRANE POTENTIAL APPROACHES THE SODIUM EQUILIBRIUM POTENTIALTHIS RADICAL CHANGE IN MEMBRANE POTENTIAL CAUSES THE SODIUM CHANNELS TO CLOSE (INACTIVATION) AND THE POTASSIUM CHANNELS TO OPEN REPOLARIZING THE MEMBRANETHERE IS A SLIGHT OVERSHOOT (HYPERPOLARIZATION) DUE TO THE POTASSIUM CHANNELS BEING MORE OPEN

GRADED VS ALL OR NONE A RECEPTORS RESPONSE TO A STIMULUS IS GRADED

IF THRESHOLD IS EXCEEDED, THE ACTION POTENTIAL RESULTING IS ALL OR NONE

PROPAGATION OF THE ACTION POTENTIAL+++++-----------------------------+++++++++++++AXON MEMBRANEINSIDEOUTSIDEACTION POTENTIALDEPOLARIZINGCURRENT

PROPAGATION OF THE ACTION POTENTIAL+++++-----------------------------+++++++++++++AXON MEMBRANEINSIDEOUTSIDEACTION POTENTIALDEPOLARIZINGCURRENT

PROPAGATION OF THE ACTION POTENTIAL--+++++------+++---------------------++++++++++AXON MEMBRANEINSIDEOUTSIDEACTION POTENTIALDEPOLARIZINGCURRENT

PROPAGATION OF THE ACTION POTENTIAL--------+++++++++++------------------++++AXON MEMBRANEINSIDEOUTSIDEACTION POTENTIALDEPOLARIZINGCURRENT

SALTATORY CONDUCTION+++++----------------+++++AXON MEMBRANEINSIDEOUTSIDEACTION POTENTIALDEPOLARIZINGCURRENTMYELINNODE OFRANVIERNODE OFRANVIER

NORMALLY A NERVE IS EXCITED BY A SYNAPSE OR BY A RECEPTORMANY NERVES SYNAPSE ON ANY GIVEN NERVERECEPTORS HAVE GENERATOR POTENTIALS WHICH ARE GRADEDIN EITHER CASE WHEN THE NERVE IS DEPOLARIZED BEYOND THRESHOLD IT FIRE AN ALL-OR-NONE ACTION POTENTIAL AT THE FIRST NODE OF RANVIER

THE SYNAPSEJUNCTION BETWEEN TWO NEURONSCHEMICAL TRANSMITTERMAY BE 100,000 ON A SINGLE CNS NEURONSPATIAL AND TEMPORAL SUMMATIONCAN BE EXCITATORY OR INHIBITORY

THE SYNAPSESYNAPTICVESSICLES INCOMINGACTION POTENTIALCALCIUM CHANNELIONCHANNELRECEPTORENZYME

THE SYNAPSESYNAPTICVESSICLES INCOMINGACTION POTENTIALCALCIUM CHANNELIONCHANNELRECEPTORENZYME

THE SYNAPSESYNAPTICVESSICLES INCOMINGACTION POTENTIALCALCIUM CHANNELIONCHANNELRECEPTORENZYME

THE SYNAPSESYNAPTICVESSICLES CALCIUM CHANNELIONCHANNELRECEPTORENZYME

THE SYNAPSESYNAPTICVESSICLES CALCIUM CHANNELIONCHANNELRECEPTORENZYME

THE SYNAPSESYNAPTICVESSICLES CALCIUM CHANNELIONCHANNELRECEPTORENZYME

THE SYNAPSESYNAPTICVESSICLES CALCIUM CHANNELIONCHANNELRECEPTORENZYME

POSTSYNAPTIC POTENTIALSRESTINGPOTENTIALEPSPTIME

TEMPORAL SUMMATIONTIMETOO FAR APART IN TIME:NO SUMMATION

TEMPORAL SUMMATIONTIMECLOSER IN TIME: SUMMATION BUT BELOW THRESHOLDTHRESHOLD

TEMPORAL SUMMATIONTIMESTILL CLOSER IN TIME: ABOVETHRESHOLDTHRESHOLD

SPATIAL SUMMATIONTIMESIMULTANEOUSINPUT FROM TWOSYNAPSES: ABOVETHRESHOLDTHRESHOLD

EPSP-IPSP CANCELLATION

NEURO TRANSMITTERSACETYL CHOLINEDOPAMINENOREPINEPHRINEEPINEPHRINESEROTONIN

HISTAMINEGLYCINEGLUTAMINEGAMMA-AMINOBUTYRIC ACID (GABA)