Here is a question I've never asked myself until now: All textbooks show synapses with a decently large synaptic cleft between the axon terminal and the dendrite. How is this connection held in place mechanically? How is the axon terminal attached to the dendrite?
The textbooks represent the synapses that way for didactic reasons. But, in fact, there are several protein complexes that keep the membranes (pre and post synaptic) attached. The most famous are the puncta adherentia junctions.
In these structures, several different proteins, like nectins and cadherins, promove cellular adhesion:
(source of the image: http://cshperspectives.cshlp.org/content/1/4/a003079)
These molecules are important not only for cellular adhesion, but for synaptic plasticity as well.