here is a summary that i found for those who didnt understand how ca+ rises the treashold : Threshold potential: largely determined by the voltage gated Na channel. In short, when membrane potential reaches the threshould, many voltage gated Na+ channels open and lead to Na+ influx and subsequent action potentials. Ca2+ ion alters the property of these voltage gated Na+ channels and make their "gating voltage" higher, aka less negative. By doing so, these Na+ channels open only at a higher voltage. Thus the threshold is raised and the difference between the resting potential and the threshold is increased. In other words, cell become less excitable.
thanks the only video on yt that explains this concept
here is a summary that i found for those who didnt understand how ca+ rises the treashold :
Threshold potential: largely determined by the voltage gated Na channel. In short, when membrane potential reaches the threshould, many voltage gated Na+ channels open and lead to Na+ influx and subsequent action potentials. Ca2+ ion alters the property of these voltage gated Na+ channels and make their "gating voltage" higher, aka less negative. By doing so, these Na+ channels open only at a higher voltage. Thus the threshold is raised and the difference between the resting potential and the threshold is increased. In other words, cell become less excitable.