Figure 1.

Cartoon of a multipolar neuron and the molecular composition of the AIS. (A) Neurons are polarized into somatodendritic and axonal domains. Axons can be myelinated by oligodendrocytes in the CNS and Schwann cells in the PNS. Nodes of Ranvier are gaps in the myelin sheath. Both axon initial segments and nodes of Ranvier have high densities of Na⁺ channels for action potential initiation and propagation, respectively. (B) The molecular organization of the axon initial segment.