COMPUTER-SIMULATION OF ACTION-POTENTIALS AND AFTERPOTENTIALS IN MAMMALIAN MYELINATED AXONS - THE CASE FOR A LOWER RESISTANCE MYELIN SHEATH
COMPUTER-SIMULATION OF ACTION-POTENTIALS AND AFTERPOTENTIALS IN MAMMALIAN MYELINATED AXONS - THE CASE FOR A LOWER RESISTANCE MYELIN SHEATH
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DOI：
10.1016/0306-4522(85)90119-8
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发表时间：
1985-01-01
期刊：
影响因子：
3.3
通讯作者：
BLIGHT, AR
中科院分区：
文献类型：
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作者：
BLIGHT, AR
去极化后电位，记录在周围神经和脊髓轴突，被解释为代表被动放电的轴膜电容。这种解释需要一个较低的阻力途径通过髓鞘比以前的测量建议。用计算机模型研究了神经纤维电特性对动作电位传导和后电位产生的贡献。该模型由一个电阻电容网络，代表一个链的20个节点。结果表明，节、节间和髓鞘的电阻插入模型后能产生合适的长度和时间常数，并能延长后电位。相似的长度和时间常数，发现使用传统的模型的轴突，从孤立的外周纤维的测量的基础上，但这并没有重现后电位。减小时间常数和增大长度常数可以提高微电极的电位传导速度。在传统模型中，通过节点的低并联电阻来满足最小化节点间时间常数的问题，而在新模型中，通过减小髓鞘的电阻来满足该问题。后一种策略要求节点泄漏电阻高于来自单光纤测量的值（约0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 250 M Ω而不是. apprx。50 M Ω）以保持长度恒定，类似于常规模型。记录电位的模拟要求髓鞘层的电阻为λ。100 Ω。cm2.该模型定量再现了轴突的电压响应注入电流脉冲和传播的动作电位，使用弗兰肯豪泽-赫胥黎动力学。通过假设刺穿部位的髓鞘中存在泄漏途径，重现了在哺乳动物记录中观察到的后电位的短持续时间分量。对于给定的节点电阻，计算出的髓鞘的较低电阻最小化了有效的节点间时间常数。这似乎使有髓纤维免于高模态漏导的替代要求。它也可能有助于更大的稳定性轴突的条件下，延长去极化，通过允许的internodal axolemma被更迅速地复极化电压依赖性K+电流，使输入电阻的internode依赖于其自身的axolemma的渗透性，比周围的髓鞘。在动作电位之后，轴膜上电荷的储存可能在调节兴奋性方面具有功能意义。
Depolarizing afterpotentials, recorded in peripheral nerves and spinal axons, were interpreted as representing passive discharge of axolemmal capacitance. This interpretation requires a lower resistance pathway through the myelin sheath than previous measurements suggested. A computer model was used to examine the contribution of the electrical characteristics of nerve fibers to action potential conduction and afterpotential generation. The model consisted of a resistance-capacitance network representing a chain of 20 internodes. The resistances of node internode and myelin sheath were found to produce suitable length and time constants and prolonged afterpotentials, when inserted into the model. Similar length and time constants were found using a conventional model of the axon, based on measurements from isolated peripheral fibers, but this did not reproduce the afterpotentials. Action-potential conduction velocity is enhanced by reducing the time constant and increasing the length constant. The problem of minimizing the internodal time constant was met in the conventional model through the low parallel resistance of the node, while in the new model it was met by reducing the resistance of the myelin sheath. The latter strategy required the nodal leakage resistance to be higher than values from single fiber measurements (.apprx. 250 M.OMEGA. rather than .apprx. 50 M.OMEGA.) to maintain the length constant similar to the conventional model. Simulation of the recorded potentials required the resistance of the myelin lamellae to be .apprx. 100 .OMEGA. cm2. The model quantitatively reproduced the voltage response of the axon to injected current pulses and to propagated action potentials, using Frankenhaeuser-Huxley kinetics. The short duration components of the afterpotential, observed in mammalian recordings, were reproduced by assuming a leakage pathway in the myelin shealth, at the impalement site. The calculated lower resistance of the myelin sheath minimized the effective internodal time constant for a given nodal resistance. This appears to free the myelinated fiber from the alternative requirement for a high modal leakage conductance. It may also contribute to greater stability of the axon under conditions of prolonged depolarization, by allowing the internodal axolemma to be repolarized more rapidly by voltage dependent K+ currents and making the input resistance of the internode dependent on the permeability of its own axolemma, more than that of the surrounding myelin sheath. The storage of charge at the axolemma following the action potential may be of functional significance in modulating excitability.