It is surprisingly hard to find information about the timing of neurons, in particular how long an action potential can contribute to the summation of a neuron. Is it on the order of milliseconds or rather seconds, i.e. for a neuron to fire, do many of the presynaptic neurons fire about at the same time?
Effective integration time of a typical neuron is in the order of 10-100 ms. You might want to look into this classic paper (read it with a critical mindset):
- Shadlen, M. N. and Newsome, W. T. (1994). Noise, neural codes and cortical organization. Curr. Opin. Neurobiol., 4:569-579.
Or some biophysics book like:
- Biophysics of Computation by Christof Koch
The length of an action potential (or spike) varies depending on several factors: refractory period, type of cell (interneurons tend to be faster) and where in the brain you are recording (in cortex both area and layer are important). Wikipedia page says something about 1ms for sodium based and 100ms for calcium based spikes.I never saw a 100ms AP, usually I record from cortex where I find AP in the range of ~1 to ~5ms.
The length of the integration however depends on too many factors, length of the dendritic tree, spatial location of the synapses, number of those synapses, strength, spine clustering, affinity and time constant of receptors, amount of Calcium, etc... the Shadlen and Newsome paper @Memming referred to is a good start. In general I'm always weary of magical numbers, if its a measurable phenomenon it's just what it is if not everithing comes with a lot of assumptions...