THE LOCAL ELECTRIC CHANGES ASSOCIATED WITH REPETITIVE ACTION IN A NON-MEDULLATED AXON
THE LOCAL ELECTRIC CHANGES ASSOCIATED WITH REPETITIVE ACTION IN A NON-MEDULLATED AXON
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DOI：
10.1113/jphysiol.1948.sp004260
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发表时间：
1948-01-01
影响因子：
5.5
通讯作者：
HODGKIN, AL
中科院分区：
文献类型：
--
作者：
HODGKIN, AL
方法所用仪器与以往文献(Hodgkin，1938；Hodgkin&Rushton，1946；Hodgkin，1947a)中描述的方法无显著差异。将一根纤维安装在三个氯化银电极上，电极的末端是细小的琼脂芯。通过10-300mq的电阻将电流施加到中心电极和相邻电极之一。从中央电极和带有高输入阻抗的直流放大器的剩余电极记录电变化。中心电极接地，并采用了通常的预防措施，以避免泄漏或人工制品。以这种方式记录的电学变化可以被认为与脉冲产生点的电学变化大致成比例。由于外部流体的短路效应，膜电位的绝对值必须减少到大约一半(Hodgkin，1947a；Hodgkin&Rushton，1946)，但这一原因并没有引起时间进程的扭曲。记录的变化被公共刺激和记录电极中的外加电流流动引起的电位下降略微扭曲。对于所采用的电极类型，这种效应的大小通常约为亚阈值电位的3%，而不到尖峰电位的1%。因此，可以安全地忽略它。另一个误差来源是中央电极的有限宽度。穿过神经膜的电位差是从中央电极的极外边缘记录的，而脉冲可能出现在极间边缘。由于电极宽度为200个数量级，中心电极两侧的膜电位差可能达到6%左右。这些轴突的合适空间常数约为2*5 mm。刺激电流由电子产生的矩形脉冲或通过Morse键施加的恒定电流组成。不应期和恢复曲线的测定是用产生两个不同间隔和幅度的短脉冲的电子电路完成的。
METHOD The apparatus employed did not differ materially from that describedin former papers (Hodgkin, 1938; Hodgkin & Rushton, 1946; Hodgkin, 1947a). A single fibre was mounted on three silver chloride electrodes which terminated in fine agar wicks. Current was applied to the central electrode and to one of the adjacent eiectrodes through a resistance of 10-300 MQ. Electrical changes were recorded from the central electrode and the remaining electrode with a dc amplifier of high input impedance. The central electrode was earthed and the usual precautions to avoid leaks or artefacts were employed. Electrical changes recorded in this way may be taken as being roughly proportional to those at the point where impulses arise. The absolute magnitude of the membrane potentials must have been reduced to about one-half by the short-circuiting effect of the external fluid (Hodgkin, 1947a; Hodgkin & Rushton, 1946) but no distortion of time course was introduced by this cause. The recorded changes were slightly distorted by the potential drop resulting from the flow of applied current in the common stimulating and recording electrode. With the type of electrode employed the magnitude of this effect normally amounted to about 3% of the subthreshold potentials and to less than 1% of the spike. It could therefore be ignored with safety. Another source of error arose from the finite width of the central electrode. The potential difference across the nerve membrane was recorded from the extrapolar edge of the central electrode whereas impulses probably arose at the interpolar edge. The difference between the membrane potentials at the two sides of the central electrode probably amounted to about 6% since the electrode width was of the order of 200/. and the appropriate space constant for these axons was about 2* 5 mm.The stimulating current consisted either of an electronically generated rectangular pulse or of a constant current applied by means of a morse key. Determinations of the refractory period and recovery curves were made with an electronic circuit which generated two short pulses of variable spacing and amplitude.