An action potential triggers the release of synaptic vesicles into the synaptic cleft by channels, allowing ions to flow into the cell, and signaling the vesicles to bind to the axonal membrane.

1. opening Voltage gated channels

2. Calcium

Explanation:

The signals are transmitted in the neurons in the form of electrical signals and which are transformed into the chemical signals at the synaptic cleft.

The electrical signal is transformed into a chemical signal when the electrical impulse reaches the terminal of the axon and opens the calcium voltage channels. The calcium which is present in a higher amount than inside enter into the terminal and allows fusion of the synaptic vesicle carrying neurotransmitter and the neurotransmitter is released into the synapse.

The neurotransmitter then binds the receptors and initiates the electrical impulse in the postsynaptic neuron.

Thus, opening Voltage gated channels and Calcium is the correct answer.