Action Potentials

Action Potentials 

changes of bioelectric potentials in an electroencephalogram or in a recording of electrical activity of other brain structures in response to stimuli arriving via the ascending or sensory tracts. A distinction is made between primary and secondary potentials or reactions. Primary action potentials or primary reactions (PR) with a short latent period arise ten to 20 milliseconds after the arrival of impulses. The PR is recorded in a limited area of the cortical projection of the receptor stimulated (for example, after the eye is stimulated by a flash of light, the PR arises in the occipital cortex in the form of monophasic or biphasic oscillations of biopotential). Secondary action potentials or secondary reactions (SR) have longer latent periods (from 30 to 200 milliseconds) and a wider region of propagation. SR arise first in the same area of the brain as the PR, but their shape is more complex, and they are polyphasic. Still more complex SR arise at the same time or later in other cerebrocortical centers (localized reactions) or even throughout the cortex (generalized reactions).

The PR is the algebraic sum of the initial changes in biopotentials of cortical neurons reacting to the first volley of im-pulses reaching the cortex from the receptor through the specific direct sensory tracts (lemniscus). The causes of local SR include reactions occurring in the corresponding cortical neurons and propagation of excitation (irradiation) along the associative neural pathways to the nearest or more distant neurons. Generalized SR are believed to arise following stimulation of the cerebral cortex through nonspecific neural pathways (from the reticular formation and limbic system).

Maps showing the cortical projection of the visual, acoustic, cutaneous, and other receptors have been constructed on the basis of recordings of PR. The origin of PR and SR is closely related to the processing of information received by the organism and formation of conditioned reflexes in the nervous system. Recordings of action potentials are used clinically to determine the precise location of a pathological process in the brain.

REFERENCES

Roitbak, A. I. “Vyzvannye potentsialy kory bol’shikh polusharii.” In the collection Sovremennye problemy elektrofiziologicheskikh issledovanii nervnoi sistemy. Moscow, 1964.
Kullanda, K. M. “Vtorichnyye bioelektricheskie reaktsii kory bol’shikh polusharii.” In the collection: Sovremennye problemy elektrofiziologicheskikh issledovanii nervnoi sistemy. Moscow, 1964.
Puchinskaia, L. M. Elektrokortikal’nye reaktsii na svet u cheloveka. Novosibirsk, 1967.

E. A. ZHIRMUNSKAIA