Action potential waveforms generated at the axon initial segment (AIS) are specialized between and within neuronal classes. But is the fine structure of each electrical event retained when transmitted along myelinated axons or is it rapidly and uniformly transmitted to be modified again at the axon terminal? To address this issue action potential axonal transmission was evaluated in a class of primary sensory afferents that possess numerous types of voltage-gated ion channels underlying a complex repertoire of endogenous firing patterns. In addition to their signature intrinsic electrophysiological heterogeneity, spiral ganglion neurons are uniquely designed. The bipolar, myelinated somata of type I neurons are located within the conduction pathway, requiring that action potentials generated at the first heminode must be conducted through their electrically excitable membrane. We utilized this unusual axonal-like morphology to serve as a window into action potential transmission to compare locally-evoked action potential profiles to those generated peripherally at their glutamatergic synaptic connections with hair cell receptors. These comparisons showed that the distinctively-shaped somatic action potentials were highly correlated with the nodally-generated, invading ones for each neuron. This result indicates that the fine structure of the action potential waveform is maintained axonally, thus supporting the concept that analog signaling is incorporated into each digitally-transmitted action potential in the specialized primary auditory afferents.

中文翻译：

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螺旋神经节轴突动作电位精细结构的模拟传输

在轴突初始段 (AIS) 生成的动作电位波形专门在神经元类别之间和内部。但是，当沿着有髓轴突传输时，每个电事件的精细结构是保持不变，还是在轴突末端快速均匀地传输以再次被修改？为了解决这个问题，在一类初级感觉传入神经中评估了动作电位轴突传递，这些传入神经拥有多种类型的电压门控离子通道，这些离子通道是复杂的内源性放电模式库。除了其标志性的内在电生理异质性外，螺旋神经节神经元还具有独特的设计。I 型神经元的双极有髓胞体位于传导通路内，要求在第一个 heminode 产生的动作电位必须通过它们的电激发膜传导。我们利用这种不寻常的轴突样形态作为动作电位传递的窗口，将局部诱发的动作电位曲线与在其与毛细胞受体的谷氨酸能突触连接处外围产生的动作电位曲线进行比较。这些比较表明，形状独特的体细胞动作电位与每个神经元的节点产生的侵入性动作电位高度相关。该结果表明动作电位波形的精细结构在轴突上保持不变，从而支持模拟信号被纳入专门初级听觉传入的每个数字传输动作电位的概念。我们利用这种不寻常的轴突样形态作为动作电位传递的窗口，将局部诱发的动作电位曲线与在其与毛细胞受体的谷氨酸能突触连接处外围产生的动作电位曲线进行比较。这些比较表明，形状独特的体细胞动作电位与每个神经元的节点产生的侵入性动作电位高度相关。该结果表明动作电位波形的精细结构在轴突上保持不变，从而支持模拟信号被纳入专门初级听觉传入的每个数字传输动作电位的概念。我们利用这种不寻常的轴突样形态作为动作电位传递的窗口，将局部诱发的动作电位曲线与在其与毛细胞受体的谷氨酸能突触连接处外围产生的动作电位曲线进行比较。这些比较表明，形状独特的体细胞动作电位与每个神经元的节点产生的侵入性动作电位高度相关。该结果表明动作电位波形的精细结构在轴突上保持不变，从而支持模拟信号被纳入专门初级听觉传入的每个数字传输动作电位的概念。