afferent fibers go to the cortex and a desire to micturate develops If it is inconvenient To pass urine, (eg, when the person is addressrg a lecture t

center sends down an impulse by which the mieturitor reflex is inhibited, so that the detrusor relaxes, the sphincter contracts and the desire disappears But a stage arrives (recall, the two ureters are pouring unne Into Ihe bladder remorselessfy), when the amount of urine to the bladder is greal, and the afferent discharges due to the sttekhing of the bladder arevery strong, at this stage the desire becomes irresistible 4 In the newborn and the nfants. the link between the cortical center and the spriai center Is not established As a result, whenever the bladder has the requisite volume of unrie, the evacuation occurs This is an example of automate bladder 5. During the act of micturition, as the urine passes through the urethra, further set of afferent impulses are produced and they reinforce the micturition reflex (this is one of the Barrington's reflexes, detailed discussion of Barringtons reflexes, however, are no longer popular in standard text books) 6. If the bladder is somewhat filled but the desire to micturate is yet to appear, but the subject decides to pass urine, he can do so This occurs, because, now, the cortex influences tie spinal centers in such a way, that micturition reflex s excited At this stage, some facts aboulthe interrelationship betwen the filling ofthe bladder and aflerent discharges and the desire to micfurate will be given 1 In the beginning, the bladder Is empty and the hydrostatic pressure (i e , the pressure within the bladder) is o( = one atmospheric pressure). 2 In the initial phases of filling, up to about 200 ml of urine accumulation, the rise of pressure Is very smart This Is because, at this stage, as Ihe urine accumulates, the detrusor relaxes to some extent and the rtseof hvdrostatic pressure in the bladder is small* Thereafter, it thses rather markedly After 500 ml of unnary accumulation, rise of pressure is sharp with even every slight degree of futher rise in urinary volume Fig. 8 4.1. in the initial phases of filing, the pressure within the bladder does not rise steeply Only in the later phase, the pressure begins to rise sharply with further rise Of bladder volume 3 Another factor e also important If sudden rise of urinary accumulation occurs, the pressure rises ratier sharply but if the urine is not passed the detrusor muscle again relaxes, and the pressure agar falls All these facts can be show expeimentaliy Maintenance of continence When the bladder is empty or oniymildhy filled, the detrusor remains relaxed and both the tnlemal and external sphincters are contracted This phenomenon, that is. the holding up of urine, is called continence and rs due to a reflex The refiex is initialed from the bladder, and at least in the species cat, the afferent impulses are conveyed by the parasympathetic afferent which terminates in the spiral efferent