Introduction

This first chapter reviews the basic structures, molecular physiology, and electro-physiology of nerve cells found in the central nervous system (CNS) and in the peripheral nervous system, including motoneurons, sensory neurons, and interneu-rons. First considered is general neuroanatomy, and the ionic and electrical properties of passive and active nerve membrane. Decremental conduction of electrical transients on passive dendrites, spatial summation of dendritic potentials, spike generation and propagation on unmyelinated and myelinated axons are described in general terms.

The anatomy and electrical properties of chemical and electrical synapses are reviewed, including the generation of excitatory postsynaptic potentials (epsps), inhibitory postsynaptic potentials (ipsps), and the quantal release of neurotransmitter at synapses and neuromuscular junctions.

The 1952 Hodgkin and Huxley (HH) dynamic, mathematical model of action potential generation is described and simulated using the general, nonlinear ordinary differential equation (ODE) solver program Simnon™. Simnon is described in Chapter 9, and is used throughout this text to model the electrical behavior of neurons and small, biological neural networks (BNNs). Simnon has been used because it has little user overhead in learning to run models on it efficiently. Simnon is also ideally suited to run chemical kinetic and pharmacokinetic (compartmental) models. Spike generation by the HH model is shown to be a nonlinear, current-to-frequency conversion process where the steady-state frequency is described by an equation of the form: f = c1 + c2 |ljm, where Ifa is the dc input current to the HH model, and m is an exponent < 1. The chapter illustrates how the basic HH model using K+ and Na+ voltage-dependent conductances can be extended to include many other types of transmembrane ion channels.

The chapter further explains how the HH model can be simply modified to create a voltage clamp system, in which negative feedback causes the transmembrane voltage, Vm, to follow a command input, Vs. HH system parameters are examined under voltage clamp conditions for ± ramp and step inputs.

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