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Dendritic spine
A dendritic spine (or spine) is a small membranous protrusion from a neuron's dendrite that typically receives input from a single synapse of an axon. Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body. Most spines have a bulbous head (the spine head), and a thin neck that connects the head of the spine to the shaft of the dendrite. The dendrites of a single neuron can contain hundreds to thousands of spines. In addition to spines providing an anatomical substrate for memory storage and synaptic transmission, they may also serve to increase the number of possible contacts between neurons.
==History==
Dendritic spines were first described at the end of the 19th century by Santiago Ramón y Cajal on cerebellar neurons.〔Ramón y Cajal, S. Estructura de los centros nerviosos
de las aves. Rev. Trim. Histol. Norm. Pat. 1, 1-10 (1888).〕 Ramón y Cajal then proposed that dendritic spines could serve as contacting sites between neurons. This was demonstrated more than 50 years later thanks to the emergence of electron microscopy.〔GRAY, E. G. Electron microscopy of synaptic contacts on dendrite spines of the cerebral cortex. Nature 183, 1592-1593 (1959).〕 Until the development of confocal microscopy on living tissues, it was commonly admitted that spines were formed during embryonic development and then would remain stable after birth. In this paradigm, variations of synaptic weight were considered as sufficient to explain memory processes at the cellular level. But since about a decade ago, new techniques of confocal microscopy demonstrated that dendritic spines are indeed motile and dynamic structures that undergo a constant turnover, even after birth.〔Dailey, M. E. & Smith, S. J. The dynamics of dendritic structure in developing hippocampal slices. J Neurosci 16, 2983- 2994 (1996).〕〔Bonhoeffer, T. & Yuste, R. Spine motility. Phenomenology, mechanisms, and function. Neuron 35, 1019- 1027 (2002).〕〔Yoshihara, Y., De Roo, M. & Muller, D. Dendritic spine formation and stabilization. Curr Opin Neurobiol (2009).〕
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