A dendritic spine is a mushroom-shaped bud that protrudes from a dendrite and forms one half of a synapse, especially in synapses of the cortex. The dendrites of cortical neurons typically are densely covered with such spines, which enable single cells to receive input from thousands of others. Spines in the human brain are about one micrometer in diameter, roughly the same as the dendrites from which they sprout, if not somewhat larger. As a result, they are too small to see with a conventional microscope, but are visible by confocal and electron microscopy. Most synapses in the human brain involve dendritic spines.
Role in synaptic plasticity
Changes in dendritic spine density underlie many brain functions, including motivation, learning, and memory. In particular, long-term memory is mediated in part by the growth of new dendritic spines to reinforce a particular neural pathway. By strengthening the connection between two neurons, the ability of the presynaptic cell to activate the postsynaptic cell is enhanced. This type of synaptic regulation forms the basis of synaptic plasticity.
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