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Slide 21

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To examine this further, we subtracted the membrane potential in the soma from the membrane potential simultaneously recorded in the axon. Shown here is a plot of membrane potential difference between the axon initial segment and the soma in a layer 5 pyramidal cell during injection of noise into the soma. Note that there is considerable variation between the membrane potential in the soma and axon (ranging from 4-8 mV). This variance will appear as a an additional variation in action potential threshold in the soma, since action potentials are actually initiated in the axon and then back-propagate into the soma.