3.1 Physiology and Electrical Activity of Muscle and Nerve Cells

|

53

ton’s equations of motion¹⁰ in addition to empirical force fields. At this scale chemical

bonds and the interaction of individual ions with, for example, functional proteins

such as ion channels can be explained. The latter methods probably offer the most ac-

curate description of the processes, but due to the limited computing power of today’s

mainframe computers, they are only able to describe small systems over very short

periods of time (ps to ns).

In biosignal processing, the description of measurable phenomena on the cellu-

lar scale and their effects on the scale of the entire organism are primarily applied.

Starting from the cellular electrophysiological processes of individual ions, the far-

field view is elaborated in the course of the chapter. Due to the analogy to AC techno-

logy we refer to the basic work by Harriehausen and Schwarzenau [26]. In the further

course of the chapter the most important facts from electrical theory and physiology

are introduced in section 3.1. The emergence and propagation of action potentials is

considered in subsection 3.1.3 and exemplified on the electrical excitation of the heart

muscle in section 3.2. Finally the chapter extends this view to biosignals in general

and concludes by a taxonomy of biosignals in section 3.3 and a section consisting of

post-reading and exercises in section 3.4.

3.1 Physiology and Electrical Activity of Muscle and Nerve Cells

Electrophysiology deals with the electrochemical signal transmission in the nervous

system, which is of great importance both in the field of clinical electrophysiology,

such as cardiology and neurology, and in experimental electrophysiology, such as

neurophysiology and muscle physiology. Electrophysiological measurements are

used in these disciplines, for example, to check nerve and muscle activity. Ion flows

in or on biological tissue are measured and evaluated. Well-known procedures are

electroencephalography, electroneurography, electromyography and electrocardio-

graphy. Cardiologists, for example, examine the electrical potential courses at the

heart muscle by measuring potentials at the body surface (non-invasive) or within

the framework of a special heart catheter examination (invasive) before implanting a

cardiac pacemaker. In addition to measuring signals, methods for stimulating these

electrophysiological systems for therapeutic and diagnostic purposes are being de-

veloped in parallel. These include, for example, the stimulation of nerve tissue in

the brain by provoking sensory stimuli, the stimulation of muscle contractions in

cardiac or gastric pacemakers, or stimulation/inhibition by pharmaceuticals. In the

latter case, the electrophysiological measurements provide important quantitative

statements about their effectiveness and applicability.

10 Equations of motion of classical mechanics, named after the English physicist and mathematician

Isaac Newton (1642-1726).