434 ACCUMULATION OF URINE MICTURITION. 



Some longitudinal fibres, which run along the upper margin of the prostate from the bladder, 

 belong to this sphincter muscle. Single transverse bundles passing forward from the surface of 

 the neck of the bladder, the transverse bands which lie within the prostate, the apex of the 

 colliculus seminalis, and a strong transverse bundle passing in front of the origin of the urethra 

 into the substance of the prostate all belong to the sphincter muscle {Henle). In the male 

 urethra, the blood-vessels form a rich capillary plexus under the epithelium, below which is a 

 wide-meshed lymphatic plexus. 



[Tonus of Sphincter Urethra. Open the abdomen of a rabbit, ligature one ureter, tie a 

 cannula in the other, and pour water into the bladder until it runs out through the urethra, 

 which is usually under a pressure of 16 to 20 inches. If the spinal cord be divided between 

 the fifth and seventh lumbar vertebra, a column of 6 inches is sufficient to overcome the 

 resistance of the sphincter, while section at the fourth lumbar vertebra has no effect on the 

 height of the pressure. In such an animal the bladder becomes distended, but in one with its 

 cord divided between the fifth and seventh lumbar vertebra?, there is incontinence of urine 

 in the former case because the excito-motor impulses are cut oft' from the centre (5 to 7 

 vert.), and in the latter because the tonus of the sphincter is destroyed (Kupressow). This 

 tonus is denied by Landois and others.] 



280. ACCUMULATION OF URINE MICTURITION. After emptying 

 the bladder, the urine slowly collects again, the bladder being thereby gradually 

 distended. [A healthy bladder may be said to be full when it contains 20 oz.] 

 As long as there is a moderate amount of urine in the bladder, the elasticity of the 

 elastic fibres surrounding the urethra, and that of the sphincter of the urethra 

 (and in the male of the prostate), suffice to retain the urine in the bladder. This 

 is shown by the fact that the urine does not escape from the bladder after death. 

 If the bladder be greatly distended (1*5 to 1*8 litre), so that its apex projects 

 above the pubes, the sensory nerves in its walls are stimulated and cause a feeling 

 of a full bladder, while at the same time the urethral opening is dilated, so that a 

 few drops of urine pass into the beginning of the urethra. Besides the subjective 

 feeling of a full bladder, this tension of the walls of the bladder causes a reflex 

 effect, so that the urinary bladder contracts periodically upon its fluid contents, 

 and so do the sphincter of the urethra and the muscular fibres of the urethra, and 

 thus the urethra is closed against the passage of these drops of urine. As long as 

 the pressure within the bladder is not very high, the reflex activity of the trans- 

 versely striped sphincter overcomes the other (as during sleep) ; but, as the pressure 

 rises and the distension increases, the contraction of the walls of the bladder over- 

 comes the closure produced by the sphincter, and the bladder is emptied, as occurs 

 normally in young children. 



As age advances, the sphincter urethras comes under the control of the will, so 

 that it can be contracted voluntarily, as occurs in man when he forcibly contracts 

 the bulbo-cavernosus muscle to retain urine in the bladder. The sphincter ani 

 usually contracts at the same time. The reflex activity of the sphincter may also 

 be inhibited voluntarily, so that it may be completely relaxed. This is the con- 

 dition when the bladder is emptied voluntarily. 



Slight movements, confined to the bladder, occur during psychical or emotional disturbances 

 (e.g., anger, fear), [the bladder may be emptied involuntarily during a fright], after stimulation 

 of sensory nerves, auditory impressions, restraining the respiration, and by arrest of the heart's 

 action. There are slight periodic variations coincident with variations in the blood -pressure. 

 The contractions of the bladder cease after deep inspiration, and also during apncea (Mosso and 

 Pellacani). The excised bladder of the frog, and even portions free from ganglia, exhibit 

 rhythmical contractions, which are increased by heat (P/alz). [Ashdown found in dogs that the 

 bladder exhibits regular rhythmical contractions, which were influenced by the degree of 

 distension of the bladder, being most marked with moderate dilatation and least when the 

 bladder was feebly or over-distended. The contractions could be registered by means of a 

 water-manometer communicating with the interior of the bladder.] 



Nerves. The nerves concerned in the retention and evacuation of the urine are : 

 1. The motor nerves of the sphincter urethra?, which lie in the pudendal nerve 

 (anterior roots of the third and fourth sacral nerves). When these nerves are divided, 

 as soon as the bladder becomes so distended as to dilate the urethral opening, the 



