Monosynaptically evoked field potential
The monosynaptic evoked field potential (English monosynaptic field potential) is an extracellularly derivable sum potential that is generated when stimulating defined monosynaptic pathways on neurons or neuron populations.
In its components, it reflects the consequence of the excitation and inhibition processes taking place on the postsynaptic membrane semiquantitatively. The cause of its development are transmembrane ion currents, which arise when the postsynaptic membrane is activated by stimulating or inhibiting synapses, as well as when action potentials are triggered and transmitted .
If z. If, for example, an electrical current enters the cell at an active membrane section, a longitudinal current flows inside the cell, which leaves the cell in certain sections depending on its passive electrical properties and flows back through the extracellular space to the origin of the transmembrane current.
The potential difference generated by the extracellular current flowing is the field potential. Knowing the position of the active synapses on the neuron and the type of transmembrane current (directed inwards or outwards) allow statements about the polarity of the potential. If a neuronal structure has a parallel arrangement of relatively elongated neurons and a zoning of the most important afferents on the dendrites , e.g. B. in the cerebral cortex , in the Ammon's horn formation ( hippocampal formation ) or in the cerebellum , it is an open field .
The field potentials of the generators arranged in the same direction add up algebraically in this case, so that when synapses that are spatially highly concentrated are stimulated, potentials of considerable magnitude can be measured (i.e. up to 20 mV). At the same time, the characteristic potential reversal is found here when a depth profile is drawn up .
In the closed fields that arise when spatially arranged neurons are activated, the situation is more complicated. The interpretation of field potentials, even in open fields, based solely on their shape and amplitude must nevertheless be carried out with caution, since they represent an algebraic summation of individual potentials. The current density analysis provides more precise quantitative descriptions.