Propagation of action potentials in inhomogeneous axon regions

  • F. Ramón
  • R. W. Joyner
  • J. W. Moore
Part of the Faseb Monographs book series (FASEBM, volume 5)


Described are studies of propagation of action potentials through inhomogeneous axon regions through experiments performed on squid giant axons and by computer simulations. The initial speed of propagation of the action potential is dependent upon the stimulus waveform. For a rectangular pulse of current, the action potential travels initially at a high speed that declines over the distance, reaching a constant speed of propagation at about 1–5 resting length constants; this distance depends on the stimulus strength. Additional experiments studied the effects of changing the axon diameter and of introducing a temperature step. It was found that the propagated action potential suffers profound modifications in shape and velocity as it reaches the region of transition. In both cases, it was possible to obtain reflected action potentials. A region of increased effective diameter was produced experimentally in the squid giant axon by insertion of an axial wire as usually employed in voltage clamps. It was found that the action potential, at the axial wire tip region, undergoes shape changes similar to those obtained in simulations of a region of increased diameter as in a junction with the axon and soma in motor neurons. It is concluded that the giant axon can be used to reproduce simple electrical behaviors in other structures.—Ramón, F., R. W. Joyner and J. W. Moore. Propagation of action potentials in inhomogeneous axon regions. Federation Proc. 34: 1357–1363, 1975.


Transmembrane Potential Voltage Clamp Cold Region Giant Axon Warm Region 
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Copyright information

© Federation of American Societies 1975

Authors and Affiliations

  • F. Ramón
    • 1
  • R. W. Joyner
    • 1
  • J. W. Moore
    • 1
  1. 1.Department of Physiology and PharmacologyDuke University Medical CenterDurhamUSA

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