EXCITATION AND INHIBITION OF PHRENIC MOTOR NEURONES

Abstract

Low intensity or low frequency electrical stimulation of the inspiratory center reproduces the same effects on phrenic neurone discharge as normal chemical activation of the respiratory center, namely increased frequency of discharge; increased duration of activity; and recruitment of inactive neurones. Stimulation of the expiratory center produces exactly the reverse effects, namely: decreased frequency of discharge; decreased duration of activity; and reduction of numbers of active neurones. Results obtained on varying stimulus intensity or frequency indicate that each phrenic motor neurone receives excitation from the inspiratory center over a number of separate pathways. The avg. level of excitation of the neurone is dependent upon the number of these pathways functioning and the frequency at which they transmit impulses. The rate at which the neurone fires is a function both of its level of excitation and the time course of recovery of excitability after it has discharged.