Internodal conduction in undissected demyelinated nerve fibres

摘要: 1. A new method is described for recording external longitudinal currents from single undissected nerve fibres in rat ventral roots. The permits identification of the sites fifteen or more successive nodes Ranvier a given fibre and measurement internodal conduction times between them.2. Average time normal root length 0.75 1.45 mm 19.7 +/- 4.6 (S.D.) musec at 37 degrees C. Internodal appeared to show minimum 1.0 mm.3. Ventral roots were demyelinated by focal application diphtheria toxin. Although markedly slowed fibres, inward membrane current remain spatially separated indicating that remains saltatory point block rather than becoming continuous as unmyelinated fibres.4. Slowing appears be due changes passive electrical properties myelin. Evidence presented suggesting there an increase capacitance decrease transverse resistance internodes fibres; such would have effect delaying excitation nodes. properties, which appear primarily vicinity nodes, consistent with pathological observed fibres.5. ranged (26 30 C) 600 musec. There great variation fibre; this presumably reflects varying severity demyelination internodes.6. As generate less when excited second two closely spaced impulses. This results increased impulse and, critically short interstimulus interval, impulse.7. refractory period transmission consequence decreased ability sustain propagation face small decreases nodal current.8. During tetanic stimulation, increases are associated corresponding generated node proximal internode question.9. It suggested magnitude during repetitive activity transmembrane concentration gradients sodium, eventual stimulation being caused intracellular sodium accumulation.10. Intracellular accumulation also offered explanation post-tetanic depression seen fibres.