PROPERTIES OF THE NEUROMUSCULAR UNIT IN RESPIRATORY MUSCLES

The time series in the logarithmic scale of the discharge interval of a NMU in respiratory muscles are divided into several parts in compliance with the respiratory cycle. The mean value (logτ^-), and the standard deviation (log S) are calculated in each part. Thus, the functional properties of the NMUs in respiratory muscles can be discussed in the same manner as the τ^--S correlation in skeletal muscles. Properties of the MNU in respiratory muscles of the dog were examined by means of the log τ^- - log S correlation under the anesthetized condition, and in forced breathing after the deafferentation by the removal of the dorsal roots and ganglions on both sides in spinal segments at Th 9∼Th 12. (1) Three or four months after the operation, the distribution of the log τ^- -log S points could be separated into two groups (the left group was designated as A, and the right group as B). (2) Under the anesthetized condition, the log τ^- - log S points belonging to the A group moved from their own region to that of the B group. (3) The points belonging to the B group in quiet breathing, were displaced to the region of the A group by forced breathing, and these points returned to their own region with the release of the load. On the contrary, no response was observed in the attitude of the points belonging to the A group in this conditioning. (4) The distributions of both groups were clearly distinguished in all activity patterns. From these results, it is presumed that the kinetic NMU and the tonic NMU are recognized in respiratory muscles as well as in skeletal muscles.