A threshold stimulus will cause the opening of voltage gated sodium ion channels that will cause further depolarizing stimulus.This stimulus will open still more voltage gated sodium ion channels.
Explanation:
Action potential: It occurs when the potential of a membrane, of a specific cell location rapidly falls and raises. This depolarization stimuli later cause adjacent location to similarly depolarize. It is produce by the special types of voltage gated ion channels present in the cell's plasma membrane.
These channels are closed when the membrane potential near resting potential of the cell which is also called negative potential, but they fastly starts to open if the membrane potential increase to a defined threshold voltage, and depolarizing the potential of transmembrane.
When the channels are open, they allow sodium ions inward flow, which cause the changes in electrochemical gradient and producing further raise in the membrane potential. This then cause more channels to open.
Yes this is true as in cold conditions our body doesn't feel the urge of water therefore we may become dehydrated not even knowing about it and of course in hot coditions we sweat therefore we loose water. Hope this helps :).
