Patterns of gamma-motoneuron activity in the external intercostal muscles of the cat during respiration

Recordings of gamma-motoneurons from fine filaments of external intercostal nerves were made during spontaneous breathing in the anesthetized cat. The patterns of alpha- and gamma-motoneuron activity varied within different areas of the rib cage. Areas of muscle which were recruited during inspiration received input from both tonically and phasically active gamma-motoneurons. Those areas of the rib cage which were not recruited during inspiration received activity from tonically active gamma-motoneurons. These patterns of gamma-motoneuron activity are in agreement with those suggested from previous recordings of muscle spindle activity.