Lecture 19 - Nervous System I

In biological systems the electrical charges are very

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In biological systems the electrical charges are very small, yet crucial All voltages are millivolts Still easily measurable The electrical potential between charges tends to make them flow producing a current The current depends on The charge difference The nature of the material through which the charge is moving  Resistance of the material through which the charge moves This is Ohm’s Law I = V/R Water  containing ions  is a very good conductor of electricity ICF and ECF are good conductors Lipids contain few charged groups and are very poor conductors (high R)
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Lipid bilayer has high resistance This means something with low resistance has to be inside the bilayer ION CHANNELS The Resting Membrane Potential All cells under resting conditions have a potential difference across their plasma  membranes with the inside of the cell being relatively negative to the outside By convention, the ECF is assigned a voltage of 0 (reference electrode) Measure whether the cell is positive or negative relative to the fluid Voltages that correlate to potentials are denoted inside relative to outside, so if the  potential difference is 70 mV, we say that the membrane potential is -70mV Neuron is relatively negative until there is an AP RP is usually -40 to -90 mV In order to induce a signal, the cell must change the RP and switch it to being relatively  positive It is important to note that RPs exist because of EXCESS charges, NOT net  charges  Resting potential exists because there is a tiny relative excess of negative ions inside  the cell and a tiny excess of positive ions outside the cell This excess is being attracted by the ions on the other side Form a thin layer on the inside and the outside of the cell Everything away from the membrane tends to be electronegative The excess s only a tiny amount of ions compared to the total amount of ions in the ECF  and ICF Cant measure the change in [] even when you indice a fairly large AP
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