[Paper Review] Penetration of action potentials during collision in the medial giant axon of the earthworm

Alfredo González‐Pérez, Rima Budvytytė+4 more|arXiv (Cornell University)|Apr 14, 2014

Neurobiology and Insect Physiology Research2 citations

TL;DR

This study investigates nerve impulse collisions in the medial giant axon of the earthworm Lumbricus terrestris and the lobster Homarus americanus, using extracellular stimulation and recording. Contrary to the Hodgkin-Huxley refractory period model, impulses do not annihilate upon collision, supporting the electromechanical soliton theory of action potential propagation.

ABSTRACT

The collisions of two simultaneously generated impulses in the giant axons of both earthworms and lobster propagating in orthodromic and antidromic direction were investigated. The experiments have been performed on the extracted ventral cords of Lumbricus terrestris and the abdominal ventral cord of lobster, Homarus americanus, by using external stimulation and recording. The collision of two nerve impulses of orthodromic and antidromic propagation didn't result in the annihilation of the two signals contrary to the common notion that is based on the existence of a refractory period in the well-known Hodgkin-Huxley theory. However, the results are in agreement with the electromechanical soliton theory for nerve pulse propagation as suggested by Heimburg and Jackson (Proc. Natl. Acad. Sci. USA 102, 9790 (2005)).

Motivation & Objective

• To examine the behavior of action potentials during collision in giant axons of earthworms and lobsters.
• To test the validity of the Hodgkin-Huxley refractory period model in predicting impulse annihilation during collision.
• To evaluate whether experimental results align with the electromechanical soliton theory of nerve impulse propagation.
• To determine if orthodromic and antidromic impulses annihilate or coexist upon collision in invertebrate giant axons.

Proposed method

• Extracellular stimulation and recording were used to generate and detect action potentials in the ventral cords of Lumbricus terrestris and Homarus americanus.
• Simultaneous orthodromic and antidromic action potentials were induced to study their interaction during collision.
• The propagation direction and timing of impulses were monitored to assess whether signals annihilated or persisted after collision.
• Results were compared against predictions from the Hodgkin-Huxley model and the electromechanical soliton theory.
• The experiments focused on the medial giant axon, known for its large diameter and fast conduction.

Experimental results

Research questions

• RQ1 Do orthodromic and antidromic action potentials annihilate upon collision in the giant axons of earthworms and lobsters?
• RQ2 How do experimental observations of impulse collision compare with predictions from the Hodgkin-Huxley refractory period model?
• RQ3 To what extent do the results support the electromechanical soliton theory of nerve impulse propagation?
• RQ4 Is the refractory period sufficient to explain the absence of signal propagation after collision in these axons?

Key findings

• Action potentials propagating in orthodromic and antidromic directions did not annihilate upon collision, contradicting the Hodgkin-Huxley model's prediction.
• The observed persistence of both impulses after collision supports the electromechanical soliton theory over the ionic current-based Hodgkin-Huxley model.
• No evidence of signal cancellation was observed, indicating that the refractory period alone does not prevent propagation in this context.
• The results are consistent with nerve impulse propagation being mediated by mechanical soliton waves rather than purely electrochemical currents.