8BB lecture 10-9-09 action potential

8BB lecture 10-9-09 action potential - What is potential...

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What is potential energy? potential energy is the “energy difference between the energy of object in a given position and its energy at a reference position”. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy , and to do work Potential energy can be thought of as energy stored .
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What is membrane potential ? consider… A separation of opposite charges = electrical potential energy = voltage The voltage across a membrane is called ‘ membrane potential All cells have voltages across their plasma (cell) membranes because of an unequal distribution of anions and cations on opposite sides of the membrane.
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To re-state… Membrane potential Is the voltage difference across a membrane Means energy is ‘stored’, (i.e., potential energy)
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Fig. 48-8 TECHNIQUE Microelectrode Voltage recorder Reference electrode A voltage recorder measures the voltage between the microelectrode tip inside the cell and a reference electrode placed in the solution outside the cell . Measuring the membrane potential of a cell
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Fig. 48-7 Inner chamber Outer chamber –90 mV 140 m M 5 m M KCI KCI K + Cl Potassium channel a) Membrane selectively permeable to K + (b) Membrane selectively permeable to Na + +62 mV 15 m M NaCI Cl 150 m M NaCI Na + Sodium channel E K = 62 mV ( log 5 m M 140 m M ) = –90 mV E Na = 62 mV ( log 150 m M 15 m M = +62 mV ) We know from measuring living cells that… The concentration of Na + is higher in the extracellular fluid than in the cytosol +
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electrochemical gradient Results from combining two forces : Chemical - the ion’s concentration gradient Electrical – the effect of membrane potential on the movement of ions Ion channels that allow the diffusion of K+ and Na+ are considered to be always open – because they are ungated. This allows an electrochemical gradient to form
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8BB lecture 10-9-09 action potential - What is potential...

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