I I 12 



HANDBOOK OF PinSIl II.OC; V 



NEnR01'H\"SIOLOGV II 



FIG. I. Regions of the right lialf of the brain stem, stimula- 

 tion of which influences respiration, shown as projected on the 

 floor of the fourth ventricle after removal of the cerebellum. 

 Vertical lining indicates areas giving inspiratory responses; 

 horizontal lining, expiratory responses. Left: Lower brain stem of 

 Macaca mulatta. [From Beaton & Magoun (i8).] Middle: Brain 

 stem of the cat, extending further cephalically than the left 

 figure. [From Pitts et al. (156).] Right: Same region of the sheep. 

 [From Amoroso et al. (7).] BC, brachium conjunctivum; 

 BP, brachium pontis; CJ, inferior colliculus; CR, restiform 

 body; M, mid-line; AC, cuneate nucleus; O, obex; TA, acoustic 

 tubercule. 



detailed expressions "increase or decrease of die 

 respiratory frequency or of the respiratory amplitude' 

 and 'displacement of the respiratory middle position 

 toward the inspiratory or the expiratory side,' in order 

 to characterize a reaction. 



tion) of certain regions, in which generally either 

 high frequencies or high intensities were used and, as 

 a rule, only strong respiratory influences were evalu- 

 ated. Furthermore, not all experimental results are in 

 agreement with the above findings. For example, 

 Brookhart (30) was unable in the dog to separate two 

 zones which could he demonstrated to yield function- 

 ally different (i.e. primarily inspiratory or expiratory) 

 respiratory reactions to stimulation. In addition, 

 action current measurements from cell elements in 

 the medulla which discharge synchronously with 

 respiration have only partially confirmed the results of 

 the stimulation experiments (i, 56, 77, 189). On the 

 other hand, in support of a separation of cell regions 

 active in inspiration and expiration may be mentioned 

 the separate relay centers for vagal inspiratory and 

 expiratory reflexes, which will be discussed in the 

 third section of this chapter. 



To the respiratory substrate in the medulla must be 

 ascribed the capability of automatic, i.e. autorhyth- 

 mic, activity. In the intact organism a regulation 

 through superimposed pontine to diencephalic, oc- 

 casionally also cortical, "respiratory centers' can be 

 regarded as certain. But the bulbar respiratory centers 

 represent, according to our present knowledge, the 

 minimal substrate with which a regulated respiratory 

 activity can he maintained and, under appropriate 

 circumstances, react to carbon dioxide stimulation or 

 other peripheral influences (182, 183). 



AN.ATOMIC.^L LOCALIZATION OF RESPIRATORY CENTERS 



Primary Respiratory Centers in tite Medulla Oblongata 



Investigations in tlic medullary region and in the 

 upper spinal cord, by means of transverse and longi- 

 tudinal sectioning, have led to the assuinption of a 

 paired respiratory center in the medulla. The results 

 of central stimulation indicate two half-centers on 

 each side, an inspiratory and an expiratory. Both are 

 localized in the reticular substance and appear not to 

 be sharply separated from one another. Nevertheless, 

 in the cat (12, 156), monkey (18) and sheep (7), the 

 anatomical substrate responsible for inspiratory ac- 

 tivity is predoininantly assigned to the medial reticu- 

 lar substance and the medial part of the lateral 

 reticular substance. Expiratory activity, on the other 

 hand, is localized in the dorsal and lateral stretches of 

 the lateral reticular substance (fig. i). One should, of 

 course, mention that these results are based primarily 

 on experiments in\ol\'ing the stimulation (or elimina- 



Primarx Respiratory Centers in the Pons 



Transverse sectioning in the region between the 

 quadrigeminal plate and the striae acusticae of the 

 medulla oblongata lead in the rabbit (33, 130, 131), 

 the cat (27, 126, 183) and the dog (101, 102, 127) to 

 respiratory changes which vary according to the lo- 

 cation of the section. After decerebration between the 

 corpora quadrigemina, spontaneous respiration is 

 hardly changed. .Sectioning of the brain stem immedi- 

 ately behind the inferior colliculi also fails to produce 

 respiratory changes, provided the cranial regions of 

 the pons remain intact. In animals with intact \'agus 

 nerves, spontaneous respiration is only slightly 

 changed when the section is made so as to remove the 

 cranial third of the pons. When, in addition, the vagus 

 nerves are cut, long periods of respiratory arrest in in- 

 spiration occur which can last several minutes. More- 

 over, maximal inspiratory depths are reached, so that 

 this forin of respiration has been characterized as con- 

 \ulsive respiration (131) or as apneustic respiration 

 (126). The inspiratory pauses are followed by more or 



