Like pulling the trigger on a gun, nothing happens until a threshold is crossed. Then something happens. This is unfortunate, as only a few specialized neuron types may actually operate in that digital manner. When the strength of an input doubles, the voltage increases. This releases neurotransmitter at a faster rate.
Inhibitory inputs decrease the voltage, thereby reducing the release rate.
Thus the neuron can release neurotransmitter at a rate determined by the sum of many positive and negative inputs, just as a savings account pays interest depending upon the balance of deposits and withdrawals. This is analog computation, not digital. No, because most spiking neurons are also analog in their computation, just using spikes for long-distance transmission of the result. The spectrum of neural computation and transmission processes can perhaps best be appreciated by first examining the so-called nonspiking neurons. Elongation over several millimeters usually means that the neuron uses impulses.