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HANDBOOK OF PH\SIOLOGV 



NEUROPHYSIOLOGY II 



that supranuclear regions influence the swallowing 

 response or can in themselves initiate a swallowing 

 movement. Part of the response to amygdaloid stimu- 

 lation is a swallowing movement (50), and Hess & 

 Magnus {47) have observed swallowing in response to 

 hypothalamic and septal stimulation. None of these 

 regions are necessary for the performance of swallow- 

 ing movements since the decerebrate animal swallows 

 if food is placed far back in the pharynx (13). Nor 

 can any of these regions or any other region inhibit a 

 swallowing movement once started. Following the 

 initiation of the movement, activation of medullary 

 and spinal nuclei follow and the activity is inde- 

 pendent of the status of the esophagus. The excitation 

 may spread to the stomach since Lorber et al. (57) 

 showed that sham feeding changed gastric motility. 

 Superior laryngeal nerve stimulation changes the 

 motility of the small intestine (5). That there may be 

 some local regulation is indicated by the fact that 

 the spinal animal shows reflex opening of the cardia 

 if the lower part of the esophagus is distended. 



G.ASTROINTESTIN.^L MOTILITY 



The empty stomach has a certain degree of tonus 

 and a Ijasic rhythm. When food enters the stomach or 

 when a distended balloon is introduced, a receptive 

 relaxation occurs which is later followed by an in- 

 crease in tone and an augmentation in frequency 

 and amplitude of the peristaltic waves. Sensory 

 stimulation, certain psychic phenomena and nausea 

 are accompanied by changes in tone and motility 

 of the gastrointestinal tract. It is apparent that both 

 central and peripheral factors participate in the con- 

 trol of gastric motility. Many attempts have been 

 made in a wide variety of animals to study the abso- 

 lute and relative role of these factors (6). 



The studies of the peripheral factors with wliich 

 we are concerned are those which refer to the central 

 projections of the distention receptors in the stomach. 

 Other peripheral impulses arising in the stomach or 

 the peritoneal cavity have been of interest. Without 

 especially studying the gastric fibers invoh'ed, 

 Bailey & Bremer (11) in 1 938 established the exist- 

 ence of vagal projections to the orbital surface. These 

 observations have been repeatedly confirmed, and 

 Dell & Olson (24) showed that there are also vagal 

 projections to the amygdaloid region. Splanchnic 

 projections and pathways have been studied care- 

 fully (1,3, 35). The projection areas for these fibers 

 were found in the somatosensory cortex (2, 26, 27). 

 Along their pathway splanchnic fibers make connec- 



tions with the reticular formation, and impulses in 

 these fibers affect the central excitatory state of the 

 brain (34, 86, 87). 



It was later shown by Paintal (67) and Iggo (48) 

 that there are tension receptors in the stomach and 

 that these send impulses via the vagus nerves. The 

 central projections of the.se end organs have not yet 

 been found. Eliasson (29) found that varying the dis- 

 tention of the stomach changed the effect of cortical 

 stimulation on gastric motility although only quanti- 

 tatively. Similar variations in response occurred on 

 stimulation of the vagus ner\es (68). It is likely that 

 the impulses aroused bv distention could influence 

 the net effect of cortical or hypothalamic stimulation 

 via the midbrain. The changes in gastric motility 

 noted by Eliasson (30) following stimulation of ex- 

 tensive areas in the midbrain may be regarded as 

 unspecific effects of reticular formation activation or 

 as eff"ects of stimulation of afferent fibers belonging to 

 different systems (23). Babkin & Bornstein (7) found 

 that vestibular stimulation may cause a rhythmic 

 type of gastric contraction which probably reflects a 

 rhythmic discharge in the reticular formation. 

 Much experimental work has been done on the ef- 

 fect of cortical stimulation on gastric motility (29, 

 50, 84, 88). Many fewer oljservations have been 

 made on its effect on intestinal motility (88). The 

 extensive cortical representation found in experi- 

 mental animals does not seem to have any counter- 

 part in man. Penfield's group has, in spite of many 

 thousands of cortical stimulations, found only the 

 area around the insula and the bands of the Sylvian 

 fissure to be connected with gastrointestinal activity 

 (72). Epileptic seizures involving a gastric aura were 

 found to have their origin in this region, and elec- 

 trical stimulation of the area led to vague gastric 

 sensation and marked changes in the electrogastro- 

 gram (71). The change could be either an increase or 

 a decrease; and, in the only case in which the insula 

 was removed and the gastrointestinal motilit\- ob- 

 served, hypermotility was noted. 



The corresponding region in animals, nameh the 

 insulo-orl)ital or orbital region, has been studied 

 extensively (10, 12, 46). Vagal aff"erents project to 

 this region; stimulation leads to inhibition of gastric 

 motility or sometimes to excitation. However, abla- 

 tion of the orbital surface seems to be without effect 

 on gastrointestinal motility (9). Hess & Akert (45) 

 obtained evidence for projection of fibers concerned 

 with oral sense to the orl^ital surface. They assumed 

 then that the orbital surface would be concerned with 

 oral defense mechanisms. The changes in gastroin- 



