Role Of Axonal Sodium-channel Band In Neural Excitability

Neuron is the basic structure and functional unit of neural system, whose electrical and biochemical activity determine the function of nerve system. Action potential (AP) is the basic internal output signal. In this paper, we reveal the general mechanism of action potential initiation (API), and study the role of sodium channel band of the axon initial segment to neural excitability.We first introduce the basic structure and electro-physiology properties of neuron, subsequently the general membrane equation of neuron and the Hodgkin-Huxley model which base on the kinetic of ion channels.Neurons receive signals from their dendrites. The fluctuations of membrane po-tential propagate to axon, determine whether initiate an AP in there. This process is so called sub-threshold propagation. In Chapter two, we aim to give the strict analytic solution of sub-threshold propagation. The variation of ion conductance is small un-der the threshold, and the conductance can approximate as a constant. We simplify the Hodgkin-Huxley equation to cable equation and analytically solve it under four ideal situation.In traditional view, when membrane potential of a neuron depolarized to a critical value, the sodium channels open and the neuron fire an spike. The critical potential is so call threshold. However, the threshold voltage is an ambiguous concept in either theories or experimental measures. In Chapter Three, we summarized several threshold and analysed the threshold of single-compartment and multi-compartment HH model.The band with dense sodium channel in axon is the primary region for action poten-tial initiation. The properties variation of sodium channel band have great influence to the excitability of neuron. In Chapter Four, we investigate the regulation by the sodium band in two types of neuron with normal weakly-excitable and fully-excitable dendrite.A summary and prospect are made in the last chapter.