BILIARY COLIC 265 



complains of pain over the right shoulder. In this case, 

 the abnormal afferent stimuli reach the fourth cervical 

 segment of the spinal medulla by the phrenic nerve (p. 128), 

 and "overflow" to the cells which are accustomed to receive 

 stimuli from the posterior supra-clavicular (supra-acromial) 

 nerves. As a result of this overflow stimulus, the patient 

 experiences pain in the skin of the shoulder. It seems 

 doubtful whether the phrenic nerve is affected in the liver 

 itself, and it is more probable that it is involved by inflammatory 

 thickening of the diaphragmatic pleura of the right side. 



The gall-bladder and the biliary passages, however, are pro- 

 vided with muscular walls, composed of unstriped muscle 

 fibres, and they can give rise to severe pain which is best 

 exemplified during an attack of biliary colic. The passage 

 or the attempted passage of a gall-stone along the bile 

 duct is accompanied by excessive peristalsis of the muscular 

 wall of the duct. As in the case of the alimentary canal, this 

 peristalsis results in the production of acute pain. 



Referred pain in connexion with the gall-bladder or bile 

 duct is experienced over the distribution of the peripheral 

 branches of the seventh, eighth and ninth intercostal nerves, 

 usually of the right side only (Fig. 96). In most cases it is 

 restricted to the anterior terminal branches, but it may spread 

 to involve the lateral branches or even the posterior rami 

 (primary divisions). The pain, therefore, is felt over an area 

 which is very similar to that affected in gastric disturbances, 

 but, in the case of the biliary passages, it tends to radiate to 

 the right side of the median plane. 



Pathological conditions of the gall-bladder or bile duct may 

 also excite a viscero-motor reflex (p. 197), which shows itself 

 as a localised contraction of the right rectus abdominis in its 

 upper part, i.e. that part of the muscle which is innervated 

 by the seventh, eighth and ninth intercostal nerves. 



The constant " overflow " of the abnormal afferent impulses 

 from the biliary passages during an attack of biliary colic may 

 establish a "focus of irritation " (p. 195) in the spinal medulla 



