1. Innervation and some electrical properties of the locust ventral diaphragm were investigated with electrophysiological and histological methods. 2. Muscle fibres are coupled electrically. Electrical stimulation evokes a graded active membrane response. 3. Each segment is innervated by four motor neurones as follows. Two motor neurones are situated in each abdominal ganglion. Branches of their axons supply the ventral diaphragm in the respective and the next posterior segment. 4. This pattern of innervation was confirmed by axonal Co and Ni staining of the motor nerve endings. 5. Neuromuscular junctions are excitatory. EPSPs show summation but no facilitation. 6. Spontaneous electrical activity of the diaphragm is to a certain degree coupled to activity of the main inspiratory muscles.

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