The spines serve to increase the surface area of the neuron and allows for more synaptic contacts. Spines also have a cytoskeleton and are believed to adjust their size and position depending on synaptic activity. Spines are mainly found on excitatory neurons and are a good way to differentiate these from the inhibitory neurons of the central nervous system. Another way of differentiating excitatory and inhibitory neurons is by the type of synapses they form. Excitatory cells form asymmetric synapses with an increased post synaptic density, in which the presynaptic terminal contains round vesicles .
Inhibitory cells form symmetric synapses in which the presynaptic elements contain flat vesicles .
Excitatory pyramidal cells of the mouse cerebral cortex and excitatory stellate cells from the primary visual cortex in monkey have the same basic components. Spiny dendrites, cell body, and an axon that has collateral branches. Inhibitory cells come in a greater variety of morphologies. The cortex in turtle has excitatory and inhibitory cells that are very similar to those found in mammals including man. Thus the same basic components are found in all vertebrate nervous systems.