730 PHYSIOLOGY OF DIGESTION AND SECRETION. 



The Nervous Control of the Intestinal Movements. There 

 is some evidence to show that the rhythmical contractions of the 

 intestines are muscular in origin (myogenic), while the more co- 

 ordinated peristaltic movements depend upon the intrinsic nervous 

 mechanism. The intestine is, however, not dependent for either 

 movement upon its connections with the central nervous system. 

 Like the stomach, it is an automatic organ whose activity is simply 

 regulated through its extrinsic nerves. 



The small intestine and the greater part of the large intestine 

 receive visceromotor nerve fibers from the vagi and the sympathetic 

 chain. The former, according to most observers, when artifically 

 stimulated cause movements of the intestine, and are therefore 

 regarded as the motor fibers. It seems probable, however, that the 

 vagi carry or may carry in some animals inhibitory fibers as well, 

 and that the motor effects usually obtained upon stimulation are 

 due to the fact that in these nerves the motor fibers predominate* 

 The fibers received from the sympathetic chain, on the other hand, 

 give mainly an inhibitory effect when stimulated, although some 

 motor fibers apparently may take this path. Bechterew and 

 Mislawski* state that the sympathetic fibers for the small intestine 

 emerge from the spinal cord as medullated fibers in the sixth dorsal 

 to the first lumbar spinal nerves, (or lower Bunch) and pass to the 

 sympathetic chain in the splanchnic nerves and thence to the 

 semilunar plexus. The paths of these fibers through the central 

 nervous system are not known, but there are evidently connections 

 extending to the higher brain centers, since psychical states are 

 known to influence the movements of the intestine, and according 

 to some observers stimulation of portions of the cerebral cortex 

 may produce movements or relaxation of the walls of the small and 

 large intestines. 



Effect of Various Conditions upon the Intestinal Move- 

 ments. Experiments have shown that the movements of the in- 

 testines may be evoked in many ways in addition to direct stimu- 

 lation of the extrinsic nerves. Chemical stimuli may be applied 

 directly to the intestinal wall. Mechanical stimulation pinching, 

 for example, or the introduction of a bolus into the intestinal 

 cavity may start peristaltic movements. Violent movements 

 may be produced also by shutting off the blood-supply, and again 

 temporarily when the supply is re-established. A condition of 

 dyspnea may also start movements in the intestines or in some 

 cases inhibit movements which are already in progress, the stimu- 

 lus in this case seeming to act upon the central nervous system and 

 to stimulate both the motor and the inhibitory fibers. Oxygen gas 



* "Archiv f. Physiologie," 1889, suppl. volume. 



