Motor innervation and pattern of activity of cat diaphragm

The segmental motor innervation of the costal and vertebral parts of the diaphragm of the cat has been studied by means of electromyography. The changes in electrical activity following successive sections of the cervical roots show that the costal region is innervated partly by C 4 but mainly by C 5 , while the vertebral part is innervated partly by C 5 and mainly by C 6 . After unilateral section of C 4 , C 5 , and C 6 no diaphragmatic electrical activity remained on the ipsilateral hemidiaphragm. Section of the right phrenic nerve in the chest eliminates all electrical activity in the ipsilateral hemidiaphragm. Following a similar section of the left phrenic nerve, some rhythmic electrical discharge is still recorded from the corresponding hemidiaphragm. Only after section of the contralateral phrenic nerve does this residual activity disappear. Therefore, a few fibers must leave the left phrenic nerve and reach the diaphragm with the right phrenic nerve. Apparently these fibers cross the midline within the diaphragm and contribute to the motor supply of its left side. The pattern of the electrical activity of the costal and vertebral parts of the diaphragm is similar. Generally, no activity is present during the last part of expiration. Submitted on July 9, 1962