PHGY 209 Lecture Notes - Lecture 3: Threshold Potential, Ion Channel, Batrachotoxin

• School: McGill University
• Department: Physiology
• Course: PHGY 209
• Professor: David Ragsdale

Document Summary

The rising (depolarizing) phase of the action potential is caused by sodium ions flowing into the cell through voltage-gated sodium channels. Sodium channels have three critical properties: they are closed at the resting membrane potential, but open when the membrane depolarizes, they are selective for na, the open channel rapidly inactivates, stopping the flow of na+ Down the whole length of the neuron"s axon membrane you have voltage gated na+ channels. When they are open they make a pore that"s selectively only permeable to na+ High concentration of na+ outside the neuron & low concentration of na+ inside the neuron so that means when sodium channels open na+ will flow into the initial segment of the axon. Na+ are closed at the resting membrane potential, open when the axon membrane is depolarized they begin to open on the threshold potential. The number of sodium channels that open depends on how much the membrane is depolarized.