Editing Functional: Neural Control of Storage and Voiding (section)

== Cerebral control of voiding ==

* See [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2897743/figure/F6/ Figure 6] for brain areas involved in the regulation of urine storage
* '''Although many factors are involved in the initiation of micturition in adults, increased intravesical pressure producing the sensation of distention is primarily responsible for the initiation of normal voluntarily induced emptying of the LUT.'''
** As the bladder fills, increasingly strong bladder afferents travel via synapses in the sacral cord to the brainstem and midbrain, where they synapse in the central periaqueductal gray and possibly PMC.
** Although the origin of the parasympathetic neural outflow to the bladder, the pelvic nerve, is in the sacral spinal cord, '''the actual coordinating center for the micturition reflex in an intact neural axis is the pontine micturition center in the rostral brainstem; efferent parasympathetic pelvic nerve activity is ultimately what is responsible for a highly coordinated contraction of the bulk of the bladder smooth musculature.'''
* '''If the trigger level is exceeded, efferent signals from the PMC descend to the sacral cord, where they excite an indirect inhibitory pathway via Onuf's nucleus that leads to sphincter relaxation and an excitatory pathway to the bladder that leads to detrusor contraction; thus voiding occurs. Therefore the spinobulbospinal voiding-reflex pathway functions as a switch, either “off” (storage) or “on” (voiding).''' '''In the absence of higher control this switching behavior would lead to involuntary bladder emptying (i.e., incontinence) whenever the bladder volume reached a critical level sufficient to trigger the brainstem switch'''
** Involuntary reflexive switching occurs in infants or in patients with neuropathic bladder when the bladder wall tension caused by increased volume of urine exceeds the micturition threshold. At this point, increased afferent firing from tension receptors in the bladder reverses the pattern of efferent outflow, producing firing in the sacral parasympathetic pathways and inhibition of sympathetic and somatic pathways, resulting in micturition. .
* White-matter damage that causes permanent incontinence appears to do so by disrupting a pathway (from medial frontal cortex to brainstem, either direct or via the thalamus) carrying the signal that maintains continence by tonically inhibiting the voiding reflex during storage