NEEVOUS MECHANISM OF MICTURITION. 



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the bladder by voluntary contraction of the abdominal muscles; 

 the diaphragm being depressed and fixed, the muscles of expira- 

 tion are put into action, and the contraction of the sphincter 

 muscle being at the same time probably checked by the will, the 

 power of retention is overcome. 



The moment the balance of power is thus turned in favor of 



Diagram of the Nervous Mechanism of Micturition. B. Bladder. M. 

 Abdominal muscles, c. Cerebral centres. R. Represents impulses which 

 pass from the bladder to the centre in the spinal cord, whence tonic impulses 

 are reflected and pass along T to sphincter, which retains the urine. When 

 the bladder is distended, impulses pass to the brain by 1, and when we will, 

 the tonus of the spinal centre stimulating the sphincter is checked, and the 

 abdominal muscles are made by 2 to force some urine into neck of bladder, 

 whence impulses pass by 3 to inhibit the sphincter centre and excite the 

 detrusor through 4. 



the expelling agencies and a drop of urine reaches the urethra, 

 the excitation thus produced brings about the complete evacua- 

 tion of the bladder without further voluntary effort. 



The nervous mechanism that controls the act of micturition 

 consists essentially of ganglionic centres which are situated in the 



