This simple axon-soma model explained how the rapid rising phase in the somatic spike is derived from the propagated axon initiated spike,
and how the somatic spike threshold variance is affected by spike propagation.
McCormick DA, Shu Y, Yu Y (2007) Hodgkin and Huxley model still standing? Nature 445:E1-E2 [PubMed]
Yu Y, Shu Y, McCormick DA (2008) Cortical action potential backpropagation explains spike threshold variability and rapid-onset kinetics. J Neurosci 28:7260-72 [PubMed]