Matters of Size

From the overall body plan of an organism to the intricate three-dimensional fold of proteins, structure is a key determinant of function. Neurons, the fundamental cells of the nervous system, are no exception. The architecture of their dendritic and axonal arbors—the cellular extensions that receive and transmit information—determines which neurons they can connect to, whereas the diameter of these extensions determines the speed and filtering of electrical signals that travel down them. Tiny femtoliter (10−15 liter)-sized protrusions from neuronal dendrites, called spines, receive a functional connection from another neuron's axon at a specialized area of contact known as a synapse. A study by Park et al. in a recent issue of Neuron (1) marks a large step forward in our understanding of how spine size and synaptic strength are balanced.