When an impulse arrives at the synaptic end bulb,the membrane becomes more permeable to [dropdown 1].The ion movement into the synaptic end bulbs causes [dropdown 2] of [dropdown 3] into the synaptic cleft.
Dropdown 1 choices:
calcium
chloride
potassium
sodium
Dropdown 2 choices:
endocytosis
exocytosis
Dropdown 3 choices:
electrons
ions
neurotransmitters
protons