What are the steps involved in the micturition cycle? How is the cycle different from the micturition reflex?
1. Decision from cortex to void
2. PMC inhibits Onuf's nucleus ( relaxes pelvic floor muscles and external urethral sphincter)
3. *Bladder descends and urine trickles into the urethra and triggers afferents
4. *Afferents activate PMC which :
- Inhibits the sympathetic preganglionics
- Activates the parasympathetic preganglionics
- Inhibits pelvic floor and external sphincter muscles
5. Afferents can also activate interneurons that
- Activate the parasympathetic pregangionics
- Inhibit Onuf's nucleus to inhibit other pelvic flood and external sphincter muscles
6. *The detrusor contracts in waves (interneuron mediated) until bladder is emptied
7. *Afferent signal an empty bladder to PMC
8. *Inhibition on Onuf's nucleus is removed pelvic floor muscles resume their supportive role, and autonomic tone maintaining continence is restored to sympathetic and parasympathetic pathways.
** micturition reflex includes these steps, but step 3 also includes strong afferent inputs from stretch receptors.