Editing Threshold potential (section)

==="Threshold electrotonus"===
A specific threshold tracking technique is ''threshold electrotonus'', which uses the threshold tracking set-up to produce long-lasting subthreshold depolarizing or hyperpolarizing currents within a membrane. Changes in cell excitability can be observed and recorded by creating these long-lasting currents. Threshold decrease is evident during extensive depolarization, and threshold increase is evident with extensive hyperpolarization. With hyperpolarization, there is an increase in the resistance of the internodal membrane due to closure of potassium channels, and the resulting plot "fans out". Depolarization produces has the opposite effect, activating potassium channels, producing a plot that "fans in".{{sfn|Burke|Kiernan|Bostock|2001|p=1581}}

The most important factor determining threshold electrotonus is membrane potential, so threshold electrotonus can also be used as an index of membrane potential. Furthermore, it can be used to identify characteristics of significant medical conditions through comparing the effects of those conditions on threshold potential with the effects viewed experimentally. For example, [[ischemia]] and depolarization cause the same "fanning in" effect of the electrotonus waveforms. This observation leads to the conclusion that ischemia may result from over-activation of potassium channels.{{sfn|Bostock|Cikurel|Burke|1998|p=150}}