NEUROMUSCULAR ORGANIZATION AND REGIONAL EMG ACTIVITY OF THE PECTORALIS IN THE PIGEON

In order to improve our understanding of the neuromuscular control of the most massive avian flight muscle, we studied the innervation patte rn of the pigeon pectoralis. Nine primary branches from the rostral tr unk and nine to ten branches from the caudal trunk of the pectoral ner ve were identified by microdissection in ten pigeons. The region of mu scle that each branch innervates was delineated by nerve stimulation s tudies (ten pigeons) and six regions were confirmed by glycogen deplet ion (ten pigeons). In pigeons, branches from the rostral nerve innerva te the anterior 3/5 of the sternobrachialis (SB) head of the pectorali s and branches from the caudal trunk innervate the posterior 1/2 of th e SB and all of the thoracobrachialis (TB). In the SB, individual bran ches of the rostral pectoral nerve innervate wedge-shaped muscle regio ns (each approximately 1.3 cm wide), collectively forming a fan-shaped arrangement along the sternal carina. Adjacent muscle regions partial ly overlap at their boundaries. Within the thoracobrachialis (TB) head of the pectoralis, muscle regions are wider. There is a region in mid -SB where the innervation territories of the rostral and caudal nerves overlap. Electromyographic (EMG) activity patterns were recorded with in ten of the identified muscle regions during take-off, level flappin g flight, and landing. Onset of EMG activity and EMG intensity within various muscle regions exhibits significant differences both within a wingbeat cycle and among different modes of flight. The innervation pa ttern of the pectoralis presents the anatomical substrate for neuromus cular compartmentalization and differential EMG activity within the pe ctoralis may reflect sensory-motor partitioning. The extent to which t he neuromuscular compartmentalization of the pectoralis corresponds to its ability to produce an array of force vectors to the wing awaits f urther more detailed biomechanical studies. (C) 1993 Wiley-Liss, Inc.