Biophysics Of The Skeletal Muscle Extracellular Potentials

The biophysics of excitable membranes and extracellular potential .fields emerged at the end of the 18th century, together with electrophysiology. and has been used ever since as a basis for the development of electrophysiological 'tnvestigations. This holds true even for the contemporary stage of initial discoveries concerning the molecular mechanisms of membrane excitability. The biophysics of ionic channels has gradually revealed the genesis of the ionic currents and of the biopotentials in ditIercnt excitable structures. On the basis of electrodynamics, the extracellular potential fields in the living body. ~nsidcred as a volume conductor, have been studied intensively. The knowledge accumulated constitutes the theoretical basis for interpretation of the electrophysiological data. Over a period of more than 15 years a group of Bulgarian investigators led by A. Gydikov has systematically studied the dependence between the intra- and extracellular potentials of the skeletal muscles. The present book summarizes these investigations known in many countries. Using a great amount of factual material from experiments and model investigations on the skeletal muscle potentials, the author considers: a) the extracellular potential field of single skeletal muscle fibres and their dependence on the parameters of intracellular action potentials, the geometric parameters ofthe fibres.and ofthe volume conductor; b) the potentials of single motor units; c) the compound and reflex muscle potentials, and d) the interference electromyogram.

One —Skeletal muscle fibre action potentials.- 1.1. First studies on action potentials.- 1.2. The contemporary membrane theory of action potentials.- 1.3. The contemporary membrane theory of excitation with respect to the action potentials of muscle fibres.- 1.4. The ionic channels.- Two — Relations between extracellular and intracellular potentials.- 2.1. Bioelectric sources and concomitant fields.- 2.2. Single cylindrical fibre. Exact solutions.- 2.3. Single cylindrical fibre. Approximate solutions.- 2.4. Discrete source approximation. The tripole model.- 2.5. Anisotropic volume conductor.- 2.6. Transmembrane (intracellular) waveshape.- Three — Dependence of the intracellular action potentials of skeletal muscle fibres on various factors.- 3.1. General characteristics of the intracellular action potentials of skeletal muscle fibres.- 3.2. Parameters of the intracellular action potentials in different types of skeletal muscle fibres and in different animal species.- 3.3. Influence of the morphological structure at the end of the muscle fibres on the propagation of the intracellular action potentials.- 3.4. Effects of various factors on the parameters of the intracellular action potentials.- 3.4.1. Blocking the contraction of the muscle fibres.- 3.4.2. Stretching of the muscle fibres.- 3.4.3. Long-lasting activity.- 3.4.4. Anoxy and the changes in pH.- 3.4.5. Short intervals between two excitations.- 3.4.6. Temperature changes.- 3.4.7. Partial block of the potassium current.- 3.4.8. Significance of the investigations of the parameters of the intracellular action potentials under the influence of various factors.- Four — Extracellular action potentials of skeletal muscle fibres.- 4.1. General characteristics.- 4.2. Influence of the finite length and of the morphology of the end on the extracellular action potentials.- 4.3. Influence of the origin of the excitation in the motor end-plates on the extracellular action potentials.- 4.4. Extracellular action potentials at different radial and axial distances.- 4.5. Extracellular potential field of active skeletal muscle fibres.- 4.6. Significance of the parameters of the space derivatives of the intracellular action. potentials to the parameters of the extracellular action potentials and the potential fields of skeletal muscle fibres.- 4.7. Vectorelectromyography of the potentials of single skeletal muscle fibres.- 4.8. Extracellular action potentials of single skeletal muscle fibres upon bipolar recording.- Five — Dependence of the extracellular action potentials of skeletal muscle fibres on various factors.- 5.1. Problems in the study of the extracellular action potentials of single skeletal muscle fibres.- 5.2. Stretching of the muscle fibre.- 5.3. Long-lasting activity.- 5.4. Ischaemia.- 5.5. Short intervals between two excitations.- 5.6. Temperature changes.- 5.7. Blocking of the ionic currents.- 5.8. Changes in the parameters of the volume &inductor.- 5.9. General conclusions regarding the changes in the intracellular and extracellular action potentials under the influence of different factors.- 5.10. Possibilities for utilizing the changes in the extracellular action potentials for evaluating the changes in the parameters of the volume conductor.- Six — Extraterritorial potentials of motor units.- 6.1. Methods of recording and basic properties of the extraterritorial potentials of motor units.- 6.2. Effective axial and radial distances of the electrode sites.- 6.3. Dependence of the extraterritorial potentials on the effective axial and radial distances.- 6.4. Velocity of propagation of the excitation in the motor units.- 6.5. Dependence of the extraterritorial potentials on the morphological characteristics of the motor units.- 6.6. Extraterritorial potential field of the motor units.- 6.7. Extraterritorial potentials beyond the territory of the motor units.- 6.8. Motor unit extraterritorial potentials upon bipolar recording.- 6.9. Extraterritorial potentials of high-threshold motor units.- 6.10. Motor unit extraterritorial potentials at long distances.- 6.11. Vectorelectromyographic images of the motor unit extraterritorial potentials.- Seven —Dependence of the motor unit extraterritorial potentials on various factors.- 7.1. Parameters of the motor unit extraterritorial potentials.- 7.2. Significance of the investigations of the motor unit extraterritorial potentials.- 7.3. Influence of the change in the length of the muscle fibres on the motor unit extraterritorial potentials.- 7.4. Motor unit extraterritorial potentials upon long-lasting activity.- 7.5. Influence of the disuse of the motor units on the extraterritorial potentials.- 7.6. Muscle ischaemia in relation to the motor unit extraterritorial potentials.- 7.7. Influence of the interimpulse interval on the motor unit extraterritorial potentials.- 7.8. Impact of muscle temperature on the motor unit extraterritorial potentials.- Eight —Motor unit intraterritorial potentials.- 8.1. Methods of recording and basic properties of the motor unit intraterritorial potentials.- 8.2. Motor unit intraterritorial potentials upon monopolar recording.- 8.3. Motor unit intraterritorial potentials upon bipolar recording.- 8.4. Dependence of the motor unit intraterritorial potentials on various factors.- Nine —Compound muscle potentials upon stimulation of the motor nerves and upon monosynaptic reflexes.- 9.1. Compound muscle potentials, recorded extraterritorially.- 9.2. Compound potentials from muscles of simple structure.- 9.3. Compound potentials from muscles of complex structure.- 9.4. Distinguishing between compound muscle potentials from near and distant muscles.- 9.5. Vectorelectromyographic images of the compound muscle potentials. Space parameters of the compound potentials.- 9.6. Dependence of the compound muscle potentials on the change in the muscle length and on the incline of the muscle fibres.- 9.7. Influence of the long-lasting activity on the compound muscle potentials.- 9.8. Influence of the interstimulus interval on the stimulation muscle potentials.- Ten —Averaged potentials of the interference electromyogram and their dependence on various factors.- 10.1. The interference electromyogram.- 10.2. General characteristics of the averaged potentials of the interference electromyogram.- 10.3. Averaged potentials of the interference electromyogram using different ways of triggering the averaging.- 10.4. Averaged potentials of the interference electromyogram recorded bipolarly and by branched electrodes.- 10.5. Influence of various factors on the averaged potentials of the interference electromyogram.- Conclusion.- References.