Dendritic spines are actin-rich protrusions from the dendritic shaft, considered to be the locus where most synapses occur, as they receive the vast majority of excitatory connections in the central nervous system (CNS). Interestingly, hippocampal spines are plastic structures that contain a dense array of molecules involved in postsynaptic signaling and synaptic plasticity. Since changes in spine shape and size are correlated with the strength of excitatory synapses, spine morphology directly reflects spine function. Therefore several neuropathologies are associated with defects in proteins located at the spines. The present work is focused on the spine actin cytoskeleton attending to its structure and function mainly in glutamatergic neurons. It addresses the study of the structural plasticity of dendritic spines associated with long-term potentiation (LTP) and the mechanisms that underlie learning and memory formation. We have integrated the current knowledge on synaptic proteins to relate this plethora of molecules with actin and actin-binding proteins. We further included recent findings that outline key uncharacterized proteins that would be useful to unveil the real ultrastructure and function of dendritic spines. Furthermore, this review is directed to understand how such spine diversity and interplay contributes to the regulation of spine morphogenesis and dynamics. It highlights their physiological relevance in the brain function, as well as it provides insights for pathological processes affecting dramatically dendritic spines, such as Alzheimer's disease.

This work was supported by the Plan Estatal de I+D+i 2013-2016 and the ISCIII Subdirección General de Evaluación y Fomento de la Investigación (Grants PI13/00408, PI10/00587 and Red HERACLES RD12/0042/0014) and FEDER Funds; FEDER Funds; Generalitat de Catalunya (SGR09-1369); and Fundació la Marató de TV3 (100310).