What is the first step in chemical synaptic transmission?

The first step in chemical synaptic transmission involves the fusion of vesicles with the presynaptic terminal. This process is crucial because it allows neurotransmitters, which have been stored in vesicles within the presynaptic neuron, to be released into the synaptic cleft. The fusion of vesicles typically occurs after an action potential reaches the presynaptic terminal, leading to an influx of calcium ions that trigger the vesicles to move toward and merge with the presynaptic membrane. This step is fundamental to the mechanism of communication between neurons, as it sets the stage for neurotransmitter release and subsequent signaling to the postsynaptic neuron. Without this step, neurotransmitters would not be released, and postsynaptic receptors would not be activated, halting the entire communication process.