342 MUSCULAR MECHANISMS OF URINARY TRACT. 



40 to 60 seconds, that is to say, the bladder rhythm is similar to the 

 spleen rhythm, first described by Roy. 1 



Since the mere accumulation of urine in the bladder increases the 

 intravesical tension and brings about rhythmic contractions, increasing 

 in force with growing distension, it would appear theoretically possible 

 that at a given distension a contraction might raise the pressure high 

 enough to overcome the resistance at the neck of the bladder, and 

 cause expulsion of the urine. According to v. Zeissl, this actually does 

 occur. This observer has found that micturition may be accomplished 

 normally in a dog after section of all the nerves to the bladder. 2 As a 

 rule, however, this evacuation will be only partial, the escape of urine 

 being checked as soon as the intravesical pressure falls below a certain 

 point. Thus, so-called incontinence of urine, which is met with in 

 various affections of the spinal cord, is invariably an overflow of urine 

 from a full bladder. 



It is evident, then, that for the normal carrying out of micturition 

 we require one or both of the following events : — 



1. A strong contraction of the muscular wall, continued until the 

 bladder is emptied. 



2. A relaxation of the " sphincter " at the neck of the bladder. 



For either or both of these events to occur, the local mechanisms of 

 the bladder must be reinforced by impulses from the central nervous 

 system. 



Nerve-supply of the bladder. — We have now to inquire into the 

 nature and paths of the impulses which reach the bladder. . The walls 

 of this organ are supplied with nerve fibres, which run to the neck of 

 the bladder from the hypogastric plexus. This plexus consists of 

 nerve fibres and small collections of ganglion cells lying in the loose 

 connective tissue on both sides of the middle part of the rectum. 

 Some ganglion cells are also found in the course of the fibres in the 

 walls of the bladder itself. The hypogastric plexus receives its fibres 

 from two sources — from the sacral nerves, and from the inferior mes- 

 enteric ganglion. 3 The branches from the sacral nerves which run to 

 the plexus are two or, more rarely, three in number, and are derived in 

 the cat from the second and third sacral nerves. They are known as 

 the nervi erigentes or pelvic nerve (Langley), and run straight to the 

 plexus without passing through the sympathetic chain. The fibres 

 from the inferior mesenteric ganglion to the plexus run in the hypo- 

 gastric nerves, two grey nerve-trunks which pass downwards on each 

 side of the rectum to take part in the formation of the plexus near the 

 neck of the bladder. The inferior mesenteric ganglion consists of four 

 small ganglia connected by fine fibres, lying round the origin of the 

 inferior mesenteric artery. This ganglion receives three nerves from 

 the lumbar sympathetic chain, and sends branches down along the 

 inferior mesenteric artery, and two fine branches upwards to the 

 superior mesenteric ganglion, and so to the solar plexus. The fibres 

 which reach the inferior mesenteric ganglion from the sympathetic 

 chain are derived from the third, fourth, and fifth lumbar nerve-roots 



1 A tracing of these contractions is given by Sherrington, Journ. Physiol., Cambridge 

 and London, 1892, vol. xiii. pi. xxii. fig. 10. 



2 Wien. liin. Wchnschr., 1896. 



3 Nawrocki and Scabitschewsky, Arch. f. d. gcs. Physiol., Bonn, 1897, Bd. xlviii. 

 S. 335. 



