I 120 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



Expiratory muscles 



M. rectus abdominis 



M. obliquus abdominis cxC. 



M. obliquus abdominis int 



M. pectoralis minor 



M. intercostalis externus, pars 



interossea, VI to X. 

 M. intercostalis inlernus, pars 



interossea et pars intercar- 



tilaginea, VI to VIII. 



Inspiratory muscles 



M. diapiiragma 



Mm. scaleni 



M. serratus post. 



M. intercostalis externus 



pars interossea, I to V. 

 M. intercostalis externus, 



pars intercartilaginea 

 M. intercostalis intcrnus, 



pars intercartilaginea, I 



to V. 



EXTRINSIC CONTROL OF RESPIR.'^TION 



A variety of nervous influences can further or in- 

 hibit the automatic activity of tlie bulbopontine 

 respiratorv centers. Thus the stretcli receptors in the 

 hings and the cliemoreceptors of the glomus caroticum 

 are directly connected with the respiratory centers 

 throu£;h afferent fibers in the vas;us and glossopharyn- 

 geal ner\es. For other receptor regions the connection 

 to the medulla is less distinct. 



\dgal Cmilivl of ResjiiralKnt 



v.-^iGAL PROPRIOCEPTIVE CONTROL. After bilateral 

 severance, or reversible blocking, of the vagus nerves 

 in the neck, the respiratory frequency decreases while 

 the amplitude increases. The minute volume is, there- 

 fore, usually hardly changed. But the immediate 

 result of vagal blocking is so strongly dependent upon 

 the technic used, the type of narcosis and the animal 

 species that quite contradictory statements on the 

 effects of vagotomy can be found in the literature. In 

 rabbits, cats and dogs, an inspiratory reaction 

 (lengthening of the duration of inspiration and an in- 

 crease in lung volume) has been described by those 

 authors who attempted to block the vagus through 

 cooling (70, 81, 123, 125). On the other hand, after 

 vagotomy or electrical blocking, expiratory reactions 

 or even long periods of respiratory arrest in expiration 

 have been described (iio, iii, 114, 166); but, re- 

 gardle.ss of the effect of the interference between the 

 loss of innervation on the one hand and a momentary 

 stimulation on the other, tracheotomized animals 

 breath more slowly after bilateral vagotomy than 

 before. Therefore, an effect tending primarily to in- 

 crease the respiratory frequency has been ascribed to 

 the vagus. As is shown in figure 5, this frequency- 

 enhancing influence is especially pronounced in the 

 guinea pig (144). 



The current concepts of the role of the afferent 



FIG. J. I'hc effect of vagotomy and of cooling of the vagus 

 nerve on respiratory rate and amplitude. Upper record: One 

 vagus cut at first signal, otfier at second. Rabbit under urethane 

 narcosis. Respiratory frequencies: 60, 50 and 30 per min.; 

 tidal air: 24, 32 and 45 ml; pulmonary ventilation: 1440, 1600 

 and 1350 ml per min. before vagotomy and after unilateral and 

 bilateral vagotomy, respectively. Lower record: Guinea pig under 

 Numal narcosis. The left vagus was sectioned and the right 

 vagus cooled to 4°C. Registration was interrupted for 5 min. in 

 the middle of the kymogram. At the end of the signal ( W) the 

 vagus was rewarmed. Prolonged vagus interruption causes ex- 

 treme reduction of respiratory frequency in this animal. In both 

 figures inspiration is downwards. Time marks are 3 sec. apart. 

 (Original records prepared by R. J. H Oberholzer.) 



vagal fibers from the lung are based, however, not so 

 much on vagotomy experiments as on the classic in- 

 vestigations by Hering & Breuer (83), Gad (70) and 

 Head (83, 84). These authors demonstrated that, 

 after closure of the trachea at the end of an inspiration, 

 the following expiration lasts considerably longer than 

 the preceding one. Conversely, when the trachea is 

 closed at the end of an expiration, the following in- 

 spiration is prolonged. Furthermore, inflation of the 

 lungs leads to a reflex expiration, while the aspiration 

 of air from the trachea or the application of a pneumo- 

 thorax elicits an inspiratory reflex. In the apneic 

 animal with an open thorax, an elevation of the dia- 

 phragm has been observed upon inflation of the lungs, 

 a lowering of the same with collapse of the lungs (88). 

 All of these reflexes are interrupted, or at least con- 

 siderably diminished, by vagotomy. Hering & Breuer 

 assumed, therefore, that two reflex effects are mediated 



