Editing Chemical synapse (section)

==Synaptic strength==<!-- This section is linked from [[Post-synaptic potential]]. See [[WP:MOS#Section management]] -->
The strength of a synapse has been defined by [[Bernard Katz]] as the product of (presynaptic) release probability ''pr'', quantal size ''q'' (the postsynaptic response to the release of a single neurotransmitter vesicle, a 'quantum'), and ''n'', the number of release sites. "Unitary connection" usually refers to an unknown number of individual synapses connecting a presynaptic neuron to a postsynaptic neuron. 
The amplitude of postsynaptic potentials (PSPs) can be as low as 0.4 mV to as high as 20 mV.<ref>{{cite journal |doi=10.2307/4134559 |vauthors=Díaz-Ríos M, Miller MW |title=Target-specific regulation of synaptic efficacy in the feeding central pattern generator of Aplysia: potential substrates for behavioral plasticity? |journal=Biol. Bull. |volume=210 |issue=3 |pages=215–29 |date=June 2006 |pmid=16801496 |url=http://www.biolbull.org/cgi/pmidlookup?view=long&pmid=16801496|jstor=4134559 |s2cid=34154835 |url-access=subscription }}</ref>  The amplitude of a PSP can be modulated by [[neuromodulators]] or can change as a result of previous activity.  Changes in the synaptic strength can be short-term, lasting seconds to minutes, or long-term ([[long-term potentiation]], or LTP), lasting hours.  Learning and memory are believed to result from long-term changes in synaptic strength, via a mechanism known as [[synaptic plasticity]].