What makes synapses stay "fixed"? What makes synapses not move or pre- and postsynaptic cells neither touch nor move away from each other? I mean the synaptic cleft is a gap between the pre- and postsynaptic cells that is about 20 nm wide (according to Wikipedia), so what makes it of that width? Are there some protein fibers anchored in both pre- and postsynaptic cells? Or do the glial cells keep them at that (often temporarily) fixed position? What prevents them from being displaced by the slightest movement of the body? I'm talking obviously about the chemical synapses. Thanks in advance for the answer.

Synapses are held together by adhesion molecules, like cadherins and neuroligins/neurexins, so they aren't just loose adjacent membrane, they are securely anchored in place.

The adhesion molecules serve both a structural and regulatory role, being important for synapse formation and plasticity.

Missler, M., Südhof, T. C., & Biederer, T. (2012). Synaptic cell adhesion. Cold Spring Harbor perspectives in biology, 4(4), a005694.