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3 Fundamentals of the Formation of Biosignals

Fig. 3.33: Different forms of sensory stimulation and their relationship to specific brain regions, as

well as the associated evoked potentials.

4.

Motor evoked potentials (MEP) used in diagnostics primarily to determine the

functional state of the nerve pathways between the primary motor cortex and the

motor neurons in the spinal cord as well as the peripheral motor nerves up to the

muscle.

Another categorisation often used for biosignals, as shown in Figure 3.34, can be de-

rived from the origin, i.e. the place of origin in the body, as well as the physical nature

of the signals. Regardless of the type of signal indicated in Figure 3.34, such signals

can still be assigned to the categories "autonomous" or "evoked" listed above, as is the

case, for example, with electrical heart activity and electrical brain activity, respect-

ively.

The physical categorisation directly results in possible measurement principles

for measuring the individual types of signals. A selection of measurement methods for

measuring electrical and non-electrical biosignals is discussed in section 4.3 using the

example of pulse measurement electrical by conductive electrodes and optically by

photoplethysmography. The aim of the conversion of a physical measurand (e.g. tem-

perature, pressure, etc.) into an electrical output variable is often the measurement

of the temporal change of the original physiological measurand as a signal curve s(t)

as well as its representation and subsequent evaluation. A wide-ranging landscape of

applications in medical technology can be found here, which include screening and