The<unk>  and initial segment have a number of specialized properties that make them capable of action potential generation, including adjacency to the<unk>  and a much higher density of voltage-gated ion channels than is found in the rest of the cell body. In dorsal root ganglion cells, the cell body is thought to have approximately 1 voltage-gated sodium channel per square micrometre, while the<unk>  and initial segment of the<unk>  have about ~100–200 voltage-gated sodium channels per square micrometre; in comparison, the nodes of Ranvier along the<unk>  are thought to have ~1000–2000 such channels per square micrometre. This clustering of voltage-gated ion channels is a consequence of plasma-membrane and cytoskeletal associating proteins such as ankyrin. In electrophysiological models, the<unk>  is included with the initial segment of the<unk>  where membrane potentials propagated from synaptic inputs to the dendrites or cell body are summed.
Axon hillock
Pocock boundary
Ulnar claw
Lines of Zahn
Collateral eminence
Ossification center
Dorsal nexus
Epiphyseal plate