Figure 7. Integration of respiratory and ‘postural’ inputs to phrenic motoneurones.

A, diaphragmatic representation of the four types of diaphragm EMG that have been identified (shown as rectified and low-pass filtered EMG). The upper trace shows a single burst of diaphragm EMG that occurs with single repetitions of upper limb flexion. In the second trace there is tonic activity in addition to superimposed phasic bursts of diaphragm EMG with repetitive upper limb movement. The third trace shows summation of inspiratory diaphragm EMG with the combined tonic and phasic modulation with repetitive upper limb movement. The lowest trace and the dashed line in the third trace show inspiratory diaphragm EMG. B, multiple inputs to the phrenic motoneurones arising from respiratory centres, (non-respiratory) higher centres and a variety of peripheral sources. Although the inspiratory drive arises predominantly from the ponto-medullary respiratory centres, ‘postural’ inputs may arise from higher centres, but during predictable repetitive movements some inputs may be reflex in origin and act at either spinal or supraspinal levels. Dashed lines indicate hypothesised inputs that have not been confirmed in the literature. (See Discussion for detail and references.)