The internodal axon membrane: electrical excitability and continuous conduction in segmental demyelination
The Journal of Physiology
|July 1, 1978
Summary
Demyelinated nerve fibers exhibit continuous conduction along internodes, a new finding that reveals electrical excitability within these segments. This phenomenon, observed in rat ventral roots, offers insights into nerve conduction in demyelinating diseases.
Area of Science:
- Neuroscience
- Cellular Electrophysiology
- Demyelinating Diseases
Background:
- Myelinated nerve fibers rely on saltatory conduction for rapid signal transmission.
- Demyelination disrupts the myelin sheath, impairing normal nerve function and leading to neurological deficits.
Purpose of the Study:
- To investigate the electrophysiological properties of demyelinated nerve fibers.
- To characterize novel modes of action potential propagation in the absence of intact myelin.
Main Methods:
- Longitudinal action currents were recorded from myelinated nerve fibers in normal and demyelinated rat ventral roots.
- Signal averaging and closely spaced electrodes were used to determine membrane currents.
- Contour plotting visualized membrane current density over space and time.
Main Results:
- Confirmed delayed saltation in demyelinated fibers.
- Observed a new phenomenon of continuous conduction along internodes, up to 1.5 times the normal internodal distance.
- Identified internodal electrical excitability and continuous conduction at significantly reduced velocities (1.1-2.3 m/sec).
Conclusions:
- Internodal electrical excitability is a feature of demyelinated nerve fibers.
- Continuous conduction arises from conduction along demyelinated axon segments.
- Findings have implications for understanding sodium channel distribution and the pathophysiology of demyelinating diseases.
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