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lecture_notes_05_(ta) - Lecture 5 The Action Potential...

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Lecture 5: The Action Potential Reading: chapter 4, section: electrical signals, pgs 92-107 (pgs 82-94, if using 3 rd edition) (TA NOTES IN RED . P LEASE NOTE THAT I AM USING AN OLD VERSION OF THE LECTURE NOTES . FIGURE AND PAGE NUMBERS REFER TO THE FIFTH E DITION OF OUR TEXT …) Action Potential - Brief all-or-nothing reversal in membrane potential (spike) , lasting on the order of 1 millisecond, that is brought about by rapid changes in membrane permeability to Na + and K + ions. Initiated in axonal or somatic membranes when the membrane potential is depolarized beyond a threshold potential and can propagate along axonal (and dendritic) membranes at a velocity that is determined by several factors. Because of their ability to propagate, action potentials are the primary mechanism used by the nervous system to transfer information over long distances (i.e. 0.1 - 1000 mm) (Figure 4-6) . ( THE AP IS AN EXAMPLE OF POSITIVE FEEDBACK ) Permeability changes - action potentials occur when Na + and K + channels in the plasma membrane open in response to depolarization. Because of their sensitivity to membrane depolarization these channels are referred to as voltage- gated channels (Figures 4-7, 4-10, 4-16) . (“ ONLY A FEW THOUSAND IONS CROSS THE MEMBRANE DURING AN AP ( AT ANY ONE LOCATION ON THE AXON ) ) Voltage-gated Na + channel - opens (activates) quickly (< .5
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