Activity patterns in respiratory muscles and in respiratory neurones of the rostral medulla of the cat.

1. In the rostral medulla the activity patterns of respiratory neurones are of two main types: inspiratory and expiratory (Fig. 1). Some expiratory neurones begin activity early enough to fit Cohen & Wang's (1959) category of ;inspiratory-expiratory'. However, in the rostral medulla, ;inspiratory-expiratory' neurones do not constitute a distinct category within the expiratory group, since all intermediate activity patterns are observed. Similarly, no distinct categories of activity patterns can be distinguished within the inspiratory group.2. Expiratory neurones are rare in the extreme medial and lateral portions of the respiratory regions on each side of the rostral medulla (Fig. 3). Respiratory neurones are not bunched in anatomical clusters within each region, though a medio-dorsal group of neurones on each side is somewhat anatomically separated from the rest.3. At any one time there are at the very least 1000 respiratory neurones on each side of the rostral medulla.4. Many of the patterns of single unit activity recorded in respiratory muscles of the nose, throat and pharynx are different from the patterns of activity typical of respiratory neurones in the medulla near the cranial motor nuclei (Figs. 1 and 4). This suggests that many of the medullary recordings are from cells other than the motor neurones innervating these muscles.