THE NERVOUS CONTROL OF INTERCOSTAL RESPIRATION

Abstract

The discharge of impulses from single motor nerve cells to the external and internal intercostal muscles of a cat has been recorded. Each contraction is the result of a short burst of impulses. Variations in depth of intercostal respiration are a result of variations in the frequency of discharge from the individual nerve cells, the duration of their discharge and the no. of nerve cells in action. The rhythmic groups of impulses in the fibers to the external intercostal muscles are generally associated with inspiration; in the fibers to the internal intercostal muscles with expiration. The discharge in the interchondral part of the internal intercostal muscle is, however, synchronous with inspiration. This rhythmic discharge of motor impulses continues when the volleys of afferent impulses resulting from respiratory movements are eliminated. The normal reciprocal character of the activity in the 2 sets of cells supplying the external and internal intercostal muscles is likewise maintained in the absence of the rhythmic afferent volleys. The relation between the frequency of discharge from the individual motor nerve cells and the intensity of stimulus has been observed by varying the degree of asphyxia. The impulse frequency increases with increasing asphyxia. During respiratory failure of an animal the frequency of impulses from these cells increases to a high value. The discharge finally fails as the result of more and more impulses dropping out of the regular rhythm which thus becomes a series of scattered volleys.