Abstract
The axon initial segment (AIS) is a highly specialized neuronal subregion that is the site of action potential initiation and the boundary between axonal and somatodendritic compartments. In recent years, our understanding of the molecular structure of the AIS, its maturation, and its multiple fundamental roles in neuronal function has seen major advances. We are beginning to appreciate that the AIS is dynamically regulated, both over short timescales via adaptations in ion channel function, and long timescales via activity-dependent structural reorganization. Here, we review results from this emerging field highlighting how structural and functional plasticity relate to the development of the initial segment, and to neuronal disorders linked to AIS dysfunction.