Dendritic spines: cellular specializations imparting both stability and flexibility to synaptic function.

Dendritic spines, the tiny protrusions that stud the surface of many neurons, are the location of over 90% of all excitatory synapses that occur in the CNS. Their small size has, in large part, made them refractory to conventional experimental approaches. Yet their widespread occurrence and likely involvement in learning and memory has motivated extensive efforts to obtain quantitative descriptions of spines in both steady state and dynamic onditions. Since the seminal mathematical analyses of D’Arcy Thompson (1992), the power of quantitatively establishing key parameters of structure has become recognized as a foundation of successful biological inquiry. For dendritic spines, highly precise determinations of structure and its variation are again proving to be essential for establishing a valid concept of function. The recent conjunction of high quality information about the structure, function, and theoretical implications of dendritic spines has, in fact, produced a flurry of