Nervous System Theory

An Introductory Study

K. N. Leibovic

• Publisher: Academic Press
• Year: 2013
• Print ISBN: 9780124412507
• eBook ISBN: 9781483267319
• Topic: Ciencias biológicas
• Subtopic: Fisiología

Nervous System Theory: An Introductory Study focuses on the nervous system theory, stressing the means for understanding the nature of the biological system rather than the elaboration of mathematical theories. This book begins with a discussion on single-cell responses, followed by a discussion of sensory information processing that leads into models of perceptual processes and their possible neural bases. This text concludes with some general principles and theoretical investigations relating to units that make up a nervous system, through a sensory pathway and central structures. The peripheral stimuli that explain the operations of the brain are also described. This publication is a good reference for neurologists, medical practitioners, and researchers conducting work on the nervous system theory.

Part One

Single Cell Responses

Outline

Chapter 1: INTRODUCTION

Chapter 2: THE RESTING POTENTIAL

Chapter 3: CABLE THEORY AND PASSIVE CONDUCTION

Chapter 4: PASSIVE RESPONSES IN DENDRITES

Chapter 5: THE ACTION POTENTIAL

Chapter 6: GRADED RESPONSES IN ACTIVE MEMBRANES

Chapter 7: SYNAPTIC COMMUNICATION

Chapter 8: REDUCED NEURON MODELS

Chapter 9: PROBABILISTIC LOGIC OF FORMAL NEURON NETWORKS

Chapter 10: CONCLUSION

Chapter 1

INTRODUCTION

Publisher Summary

The nerve cell is distinguished from other cells by having a number of long, fibrous processes emanating from the cell body and by its ability to generate and transmit signals. Of these the axonal signals are of constant amplitude and variable frequency, whereas the dendritic ones decay in amplitude as they spread along the fiber. This chapter discusses the resting potential and the transmission of signals in axons and dendrites. It discusses the synaptic communication and some reduced models of neuron function. It is found that different problems necessitate the formulation of different models. For example, in the treatment of the resting potential, the ionic flows are divided into components due to diffusion and the electric potential, whereas in the treatment of the cable properties of a nerve fiber, all the flows are considered as electric current dependent on conductance, capacitance, and potential. Again in the treatment of active membranes, the ionic flows are separated into species components, each with its own conductance and driving force expressed in terms of potentials.

The nerve cell is distinguished from other cells by having a number of long, fibrous processes emanating from the cell body and by its ability to generate and transmit signals. Of these the axonal signals are of constant amplitude and variable frequency, whereas the dendritic ones, as a rule, decay in amplitude as they spread along the fiber. In both cases the signals are in the form of changes of membrane potential. In the resting state the potential inside the cell is some 50–90 mV below that outside the cell. This potential difference is regulated by differences of ionic concentration.

The cell membrane is 50–100 Å thick and separates two aqueous solutions of which the one outside is rather more electroconductive than the one inside. The sodium and chloride ion concentrations in the external medium are about 10 times as high as those inside the cell, whereas the potassium ion concentration inside the cell is about 30 times that outside. The permeability of the cell membrane is low but the K⁺ and CI⁻ ions move through it much more readily than the Na⁺ ions, whose normal leakage into the cell is counteracted by the metabolically driven “sodium pump.”

If the ionic permeabilities of the membrane are fixed, then a change of polarization produced at some point on a fiber will spread and decay as it is conducted “electrotonically,” as in a passive, leaky cable. In an active fiber, on the other hand, the ionic permeabilities depend on the state of polarization of the membrane, and a pulse of depolarization can be regenerated as it is conducted along the fiber. Thus, in an axon, when the resting potential of the initial segment is raised above a certain threshold value, the depolarization is rapidly amplified, producing a “spike,” or action potential, which travels along the axon with constant amplitude. This is based on the following mechanism (Hodgkin and Huxley, 1952). The depolarization of the membrane increases Na⁺ permeability, whereupon external Na⁺ ions rapidly enter the cell and amplify the initial depolarization. With only a brief delay, however, the K⁺ permeability is increased and K⁺ flows out of the cell, while the Na⁺ permeability is reduced to its former value, returning the membrane potential toward the resting lev...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• PREFACE
• ACKNOWLEDGMENTS
• Part One: Single Cell Responses
• Part Two: Information Processing in a Sensory Pathway
• Part Three: Models of Perceptual Function
• Part Four: Some General Considerations
• AUTHOR INDEX
• SUBJECT INDEX