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 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.
