Action potential initiation site depends on neuronal excitation

Rosemary Melinek, Kenneth J. Muller

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


The initiation site in neurons is where the excitatory and inhibitory inputs sum to generate action potentials. It is generally considered to be at a fixed location, typically at the axon hillock or initial segment, although action potentials, or impulses, could in theory arise at a site that shifts dynamically. The data reported here show that the initiation site can shift in a graded manner, by as much as 175 μm, depending on the level of neuronal excitation. Laser axotomy reveals that the Anterior Pagoda (AP) neuron of the leech is excitable within the synaptic neuropil before its axon bifurcates. Using an electrophysiological technique to measure relative delays in impulses arriving at different sites, we have found that depolarization, either by applied current or by synaptic input, can shift the site of impulse initiation in the cell proximally toward the soma- and neurites receiving synaptic input. Impulse initiation in this region should enhance the efficacy of inputs synapsing there. Conversely, hyperpolarization can shift the initiation site distally. A shifting initiation site, therefore, may be a mechanism by which synaptic inputs can rapidly enhance or suppress the active response of the AP neuron to other synaptic inputs.

Original languageEnglish (US)
Pages (from-to)2585-2591
Number of pages7
JournalJournal of Neuroscience
Issue number8
StatePublished - Apr 15 1996


  • dendritic action potential
  • impulse initiation site
  • laser axotomy
  • leech
  • postsynaptic regulation
  • synaptic integration

ASJC Scopus subject areas

  • Neuroscience(all)


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