Ephaptic Transmission
Pronunciation: eh-FAP-tick
Abnormal electrical communication between adjacent nerve fibers due to demyelination, causing inappropriate activation of neighboring axons. Results in characteristic electrodiagnostic findings in demyelinating neuropathies.
Full Definition
Ephaptic transmission is a pathological form of nerve conduction that occurs when demyelinated nerve fibers develop abnormal electrical coupling with adjacent fibers. In normal nerves, myelin provides electrical insulation between axons, preventing cross-talk. When myelin is damaged or lost, electrical current can jump from one axon to another, causing inappropriate activation of neighboring nerve fibers. This phenomenon can produce several electrodiagnostic abnormalities, including A-waves (late responses due to indirect activation), abnormal F-waves, and sometimes facial synkinesis in patients with facial nerve lesions. Ephaptic transmission is most commonly observed in demyelinating conditions such as Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy (CIDP), and focal nerve compression syndromes.
Usage
Usage note: Pronounced with emphasis on the second syllable. Often associated with A-waves in electrodiagnostic reports.
In Context
- "The presence of A-waves suggested ephaptic transmission between demyelinated fibers." — Nerve conduction study interpretation
- "Ephaptic transmission explained the paradoxical facial movements observed during voluntary contraction." — Clinical neurophysiology report