In micturition reflex, the first change to occur is _______
One of the initial events is the relaxation of the muscles of the pelvic floor, and this may cause a sufficient downward tug on the detrusor muscle to initiate its contraction. Micturition Reflex Micturition is fundamentally a spinal reflex facilitated and inhibited by higher brain centers and is subject to voluntary facilitation and inhibition. These centers include Strong facilitative and inhibitory centers in the brain stem, located mainly in the pons Several centers located in the cerebral coex that is mainly inhibitory but can become excitatory. The micturition reflex is the basic cause of micturition, but higher centers normally exe final control of micturition. Micturition reflex is the result of a stretch reflex initiated by sensory stretch receptors in the bladder wall, especially by the receptors in the posterior urethra when this area begins to fill with urine at the higher bladder pressures. Sensory signals from the bladder stretch receptors are conducted to the sacral segments of the cord through the pelvic nerves and then reflexively back again to the bladder through the parasympathetic nerve fibers by way of these same nerves. As the bladder continues to fill, the micturition reflexes become more frequent and cause greater contraction of the detrusor muscle. Once a micturition reflex begins, it is &;self-regenerative&; It is a single complete cycle of The progressive and rapid increase of pressure A period of sustained pressure and Return of the pressure to the basal tone of the bladder. As the bladder becomes more and more fiilled, micturition reflexes occur more and more often and more and more powerfully. Once micturition reflex becomes powerful enough, it causes another reflex, which passes through the pudendal nerves to the extrenal sphincter to inhibit it. If this inhibition is more potent in the brain than the voluntary constrictor signals to the extrenal sphincter, urination will occur. If not, urination will not occur until the bladder fills still fuher and the micturition reflex becomes more powerful. Ref: Guyton and Hall 13th edition Pgno: 329-330
Trigone relaxation
Detrusor contraction
Relaxation of perineal muscles
Decreased urethral pressure
Renal physiology