Threshold potential

 Threshold potential

An action potential can be generated along the axon while the threshold potential is reached. The greater the strength of the stimulus, causing the membrane depolarisation process to occur. Subsequently, some voltage-gated Na+ channels are opened, allowing the Na+ ions to move across the membrane into the intracellular environment. The neuronal membrane now becomes slightly positive, relative to the outside of membrane. As the membrane potential shift from -70mV to more positive value, the threshold potential is reached, causing all of the voltage-gated Na+ channel to open, creating a rapid rise of membrane potential value into the maximum, +60mV. During depolarisation, the membrane potential value would not exceed the amount of +60mV as it is the equilibrium potential of Na+.

References http://people.eku.edu/ritchisong/301notes2.htm