

EFFECT OF NERVES ON MICTURITION. 435 



urine begins to trickle away (incontinence of urine). 2. The sensory nerves of the 

 urethra, which excite these reflexes, leave the spinal cord by the posterior roots of 

 the third, fourth, and fifth sacral nerves. Section of these nerves causes incon- 

 tinence of urine. The centre in dogs lies opposite the fifth, and in rabbits, oppo- 

 site the seventh, lumbar vertebra (Budge). 3. Fibres pass from the cerebrum 

 those that convey voluntary impulses through the peduncles, and the anterior 

 columns of the spinal cord (according to Mosso and Pellacani, through the posterior 

 columns and the posterior part of the lateral columns), to the motor fibres of the 

 sphincter urethrae. 4. The inhibitory fibres concerned in the reflex-inhibition of 

 the sphincter urethras, take the same course (perhaps from the optic thalamus 1) 

 downwards through the cord to where the third, fourth, and fifth sacral nerves 

 leave it. 5. Sensory nerves proceed from the urethra and bladder to the brain, 

 but their course is not known. Some of the motor and sensory fibres lie for a part 

 of their course in the sympathetic. 



Transverse section of the spinal cord above where the nerves leave it, is 

 always followed in the first instance by retention of urine, so that the bladder be- 

 comes distended. This occurs because (1) the section of the spinal cord increases 

 the reflex activity of the urethral sphincter ; and (2), because the inhibition of this 

 reflex can no longer take place. As soon, however, as the bladder becomes so dis- 

 tended, as in a purely mechanical manner to cause dilatation of the urethral orifice, 

 then the urine trickles away, but the amount of urine which trickles out in drops 

 is small. Thus the bladder becomes more and more distended, as the continuously 

 distended walls of the organ yield to the increased tension, so that the bladder may 

 become distended to an enormous extent. The urine very frequently becomes 

 ammoniacal, accompanied by catarrh and inflammation of the bladder ( 263). 



Voluntary Micturition. Observers are not agreed as to the mechanism con- 

 cerned in emptying the bladder when it is only partially full. It is stated by some 

 that a voluntary impulse passes from the brain along a cerebral peduncle, and the 

 cord, to the anterior roots of the 3rd and 4th sacral nerves, and partly through 

 motor fibres from the 2nd to the 5th lumbar nerves (especially the 3rd), to act 

 directly upon the smooth muscular fibres of the bladder. This is assumed, because 

 electrical stimulation of any part of this nervous channel causes contraction of the 

 bladder. This view, however, does not seem to be the true one. It is to be re- 

 membered that Budge showed that the sensory nerves of the wall of the bladder 

 are contained in the first, second, third, and fourth sacral nerves, and also in part 

 in the course of the hypogastric plexus, whence they ultimately pass by the rami 

 communicantes into the spinal cord. 



According to Landois, the smooth musculature of the bladder cannot be excited 

 directly by a voluntary impulse, but it is always caused to contract reflexly. If we 

 wish to micturate when the urinary bladder contains a small quantity of urine, 

 we first excite the sensory nerves of the opening of the urethra, either by causing 

 contraction or relaxation of the sphincter urethras, or by means of slight abdominal 

 pressure, and thus force a little urine into the urethral orifice. This sensory 

 stimulation causes a reflex contraction of the walls of the urinary bladder. At 

 the same time, this condition is maintained voluntarily, by the action of the intra- 

 cranial reflex-inhibitory centre of the sphincter urethras. The centre for the reflex 

 stimulation of the movements of the walls of the urinary bladder is placed some- 

 what higher in the spinal cord than that for the sphincter urethras. In dogs, it is 

 opposite the 4th lumbar vertebra (Gianuzzi, Budge). 



[Two centres are assumed to exist in the cord, fig. 292, one the automatic (A.C.) at the segment 

 corresponding to the 2nd, 3rd, and 4th sacral nerves, which maintains the tonic action of the 

 sphincter ; the other, a reflex centre (R.C.), is situated higher, and through it the detrusor urinas 

 is excited to contraction. Both centres are connected to and governed or controlled by a cerebral 

 centre (C. ). The automatic centre is connected with the sphincter, and the other with the urine- 

 expelling fibres. They are also connected with afferent fibres from the bladder and elsewhere. 



