West D C, Wolstencroft J H
J Physiol. 1983 Apr;337:37-50. doi: 10.1113/jphysiol.1983.sp014610.
Strength-duration characteristics for the stimulation of 131 raphespinal and reticulospinal axons in the spinal cord were determined using two types of stimulating electrode. Conduction velocity of these fibres ranged from 0.86 to 63 m/s. With silver wire (250 micron diameter) stimulating electrodes, chronaxies were: 0.18 +/- 0.06 ms for axons conducting between 16 and 63 m/s, 0.4 +/- 0.22 ms for axons conducting between 5 and 15 m/s and 2.06 +/- 0.79 ms for those with conduction velocity less than 5 m/s. There was an inverse relationship between chronaxie and conduction velocity. Rheobase values ranged from 7.4 to 400 microA but were independent of conduction velocity. Chronaxies obtained with wire electrodes were compared with those from stimulation of the same fibre through saline-filled micropipettes (2-12 micron tip diameter). Rheobase values with the micropipettes ranged from 1.6 to 20 microA, indicating a close proximity of the pipette to the axon. For these axons, chronaxies from metal wire electrodes ranged from 0.12 to 2.4 ms and for micropipettes from 0.04 to 0.65 ms. In almost all cases, chronaxies for micropipette stimulation were lower than those for metal wire electrodes. Furthermore, with micropipettes chronaxies were independent of conduction velocity. The results are shown to be related to differences in time constant of the activated region of axon and charge requirements of threshold activation. The two stimulating conditions, i.e. micro-electrodes compared with wire electrodes, are analogous to the theoretical point stimulated cable and uniformly polarized membrane cases. The results are discussed in relation to the possibility of determination of fibre type from stimulation characteristics. A distinction between chronaxies of myelinated and non-myelinated fibres can be made using wire electrodes of 250 micron diameter, but not with micro-stimulation, as with micropipettes (2-12 micron diameter).
使用两种类型的刺激电极测定了脊髓中131条中缝脊髓和网状脊髓轴突的强度-时间特性。这些纤维的传导速度在0.86至63米/秒之间。使用直径250微米的银丝刺激电极时，时值如下：传导速度在16至63米/秒之间的轴突为0.18±0.06毫秒，传导速度在5至15米/秒之间的轴突为0.4±0.22毫秒，传导速度小于5米/秒的轴突为2.06±0.79毫秒。时值与传导速度呈反比关系。基强度值范围为7.4至400微安，但与传导速度无关。将使用金属丝电极获得的时值与通过充满盐水的微吸管（尖端直径2至12微米）刺激同一纤维获得的时值进行了比较。微吸管的基强度值范围为1.6至20微安，表明微吸管与轴突非常接近。对于这些轴突，金属丝电极的时值范围为0.12至2.4毫秒，微吸管的时值范围为0.04至0.65毫秒。几乎在所有情况下，微吸管刺激的时值都低于金属丝电极的时值。此外，使用微吸管时，时值与传导速度无关。结果表明与轴突激活区域的时间常数和阈值激活的电荷需求差异有关。两种刺激条件，即微电极与金属丝电极相比，类似于理论上的点刺激电缆和均匀极化膜的情况。讨论了根据刺激特性确定纤维类型的可能性。使用直径250微米的金属丝电极可以区分有髓纤维和无髓纤维的时值，但对于微刺激（如使用直径2至12微米的微吸管）则无法区分。
