Physiology of urination
This is initiated by the micturition reflex which include the following events
If the micturition reflex is powerful enough it generates another micturition reflex and which passes through the pudendal nerve to inhibit the external urethral sphincter. Urination occurs when the inhibition is less for the urethral sphincter than for the reflex. The urinary bladder then empties itself. The micturition reflex is controlled from the micturition center probably in the pons.
Internal urethral sphincter exists only in the male and it prevents retrograde ejaculation and it contracts when its contained α1 adrenoceptors are stimulated. Urine is stored in the bladder when the detrusor relexases and the sphincters close.
These centers maintain a hold on micturition as follows
© Electronic School of Medicine
Creator: Oluwole Ogunranti