238 



Tlir INTHRNAL FNVIRONMnNT OF IHF BODY 



Part III 



RESPIRA TORY 

 CENTER 



VAGUS NERVE 



[AFFeRENT] 



LUNG 



J— MEDULLA 

 SPINAL CORD 



RIB 



INTERCOSTAL 

 NERVE- 



[EFFERENT] 



& MUSCLE- 



Expiration 



Inspiration 



B 



Fig. 13.13. A, Some of the nerves connected with human breathing. All of 

 the structures shown are symmetrical on both sides. The intercostal muscles move 

 the ribs out and up. Volleys of impulses are discharged rhythmically from the 

 paired clusters of nerve cells in the respiratory center in the medulla or brain 

 stem. These pass through the spinal cord to the intercostal muscles, and through 

 the vagus and phrenic nerves to the lungs and diaphragm. B, Intercostal muscles 

 lift the ribs out and up as the handle of a pail is lifted. {A, reprinted from 

 The Machinery of the Human Body by Carlson and Johnson, by permission of 

 The University of Chicago Press. Copyright 1948. B, courtesy, Gerard: The Body 

 Functions. New York, John Wiley and Sons. 1941.) 



