How many inputs are needed to excite/saturate a neuron

[Doron Tal]

On the one hand, anatomical evidence suggests that a neuron has, on
average, on the order of THOUSANDS of neurons impinging on it.  On the
other hand, physiological evidence shows that only a few epsps are
needed to generate an action potential - which would imply that ONE
cell is sufficient for exciting the postsynaptic neuron.

Can anyone explain this disparity between anatomy and physiology?

Some hypotheses:

1. most of the thousands of synapses on a neuron are inactive
(unlikely)
2. a neuron that has thousands of inputs has an extremely large and
finely-tuned range

If we knew what the range of a neuron is, on average, then we'd be
able to tell between the two above hypotheses.

-Doron