神经冲动抵达末梢时,引起递质释放主要是哪种离子的作用( )

A、C1[img=~\/QImg\/2013-06-27-14-49-35\/image007.gif]
B、Ca[img=~\/QImg\/2013-06-27-14-49-35\/image006.gif]
C、Mg[img=~\/QImg\/2013-06-27-14-49-35\/image006.gif]
D、Na[img=~\/QImg\/2013-06-27-14-49-35\/image001.gif]
E、K[img=~\/QImg\/2013-06-27-14-49-35\/image001.gif]