The actin cytoskeleton directly determines the morphology of the spine, and actin regulators, small GTPases such as Rac, RhoA, and CDC42, rapidly modify this cytoskeleton. Because spines have a cytoskeleton of primarily actin, this allows them to be highly dynamic in shape and size. tubulin Monomers and microtubule-associated proteins (MAPs) are present, and organized microtubules are present. The cytoskeleton of dendritic spines is primarily made of filamentous actin ( F-actin).
These changes in shape might affect the electrical properties of the spine. The cytoskeleton of dendritic spines is particularly important in their synaptic plasticity without a dynamic cytoskeleton, spines would be unable to rapidly change their volumes or shapes in responses to stimuli. Hippocampal and cortical pyramidal neurons may receive tens of thousands of mostly excitatory inputs from other neurons onto their equally numerous spines, whereas the number of spines on Purkinje neuron dendrites is an order of magnitude larger. Dendritic spines occur at a density of up to 5 spines/1 μm stretch of dendrite. Spines are found on the dendrites of most principal neurons in the brain, including the pyramidal neurons of the neocortex, the medium spiny neurons of the striatum, and the Purkinje cells of the cerebellum. Excitatory axon proximity to dendritic spines is not sufficient to predict the presence of a synapse, as demonstrated by the Lichtman lab in 2015. The variable spine shape and volume is thought to be correlated with the strength and maturity of each spine-synapse.ĭendritic spines usually receive excitatory input from axons, although sometimes both inhibitory and excitatory connections are made onto the same spine head. Electron microscopy studies have shown that there is a continuum of shapes between these categories. The most notable classes of spine shape are "thin", "stubby", "mushroom", and "bifurcated". Spines with strong synaptic contacts typically have a large spine head, which connects to the dendrite via a membranous neck. Structure ĭendritic spines are small with spine head volumes ranging 0.01 μm 3 to 0.8 μm 3. It has also been suggested that changes in the activity of neurons have a positive effect on spine morphology. 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. The dendrites of a single neuron can contain hundreds to thousands of spines. 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. Dendritic spines serve as a storage site for synaptic strength and help transmit electrical signals to the neuron's cell body. A dendritic spine (or spine) is a small membranous protrusion from a neuron's dendrite that typically receives input from a single axon at the synapse.
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