Editing Functional: Neuromodulation (section)

== Neurophysiology of Electrical Stimulation For Storage And Emptying Disorders ==

* '''The acquired and unique ability to void volitionally is due to either negative feedback (inhibition of voiding) or positive feed-forward (induction of voiding) influences of supraspinal inputs from the pontine micturition center on this sacral micturition reflex pathway.'''
** Bladder afferent nerve signaling sends information about pain and bladder fullness to the brain that will in turn initiate the micturition reflex.
*** Any loss of either central supraspinal inhibitory influences or increased sensitization of bladder afferent signaling can lead to unmasking of involuntary voiding.
**** Bladder overactivity may be in part mediated by the loss of voluntary control of the voiding reflex and, furthermore, emergence of primitive voiding reflexes.
**** In certain states of neurologic or inflammatory disease of the bladder, the previously silent C fibers may emerge and trigger the micturition reflex. Accordingly, blockade of this pathway by electrical neuromodulation, similar to pharmacologic blockade by capsaicin (a C-fiber blocker), may suppress detrusor overactivity (DO)
* '''Reflexes That Promote Bladder Storage''' [note that this description is slightly different than CW11 Chapter 69 description]
** '''Guarding reflex'''
*** '''Guards or prevents urine loss from times of cough or other physical stress that would normally trigger a micturition episode.'''
*** Under somatic influence
*** Suprapontine input from the brain turns off the guarding reflex during micturition to allow efficient and complete emptying.
** '''Bladder afferent reflex'''
*** '''Promotes continence during periods of bladder filling and is quiet during micturition''' (similar to the guarding reflex)
*** '''Works through sacral interneurons that then activate storage through pudendal nerve efferent pathways directed toward the urethral sphincter.  '''
*** Under sympathetic tone
* Reflexes That Promote Bladder Emptying
** Signals from the bladder that may modulate the need to void with fullness, pain, pressure, or stretch may elicit bladder afferent activity through the Aδ or even C fibers.
*** These bladder afferent nerve fibers then synapse with both parasympathetic efferents (bladder-bladder reflex) and parasympathetic urethral efferents (bladder-urethral) reflex.
** The urge to void may then be translated as an initial activity (inhibitory) of the bladder-urethral reflex to allow the pressure in the urethral outlet to drop immediately before a bladder contraction ensues and simultaneously permit the bladder-bladder reflex to allow a smooth bladder contraction to occur as the reflex is maintained throughout the entire void
* '''Putative Mechanism of Action of Sacral Neuromodulation'''
** '''Activation of somatic sacral afferent inflow at the sacral root level that in turn affects the storage and emptying reflexes in the bladder and central nervous system accounts for the positive effects of neuromodulation on both storage and emptying functions of the bladder'''
* '''Putative Mechanism of Action of Sacral Neuromodulation in Overactive Bladder'''
** Inhibition by electrical neuromodulation may, in part, modulate the sensory outflow from the bladder through the ascending pathways to the pontine micturition center, thereby preventing involuntary contractions
** '''By modulating the micturition reflex circuit but allowing voluntary voiding to occur, sacral neuromodulation may affect and improve the abnormal bladder sensations, involuntary voids, and detrusor contractions but still maintain normal bladder sensations and voluntary voiding patterns.'''
* '''Putative Mechanism of Action of Sacral Neuromodulation in Urinary Retention'''
** Sphincteric activity can be turned off by brain pathways to allow efficient and complete bladder emptying.
** If the suprasacral pathways are altered, the guarding and urethral reflexes still exist and cannot be turned off. This may cause retention, as in the spinal cord–injured patient who in turn has detrusor-sphincter dyssynergia resulting in urinary retention. Thus, '''inhibition of the guarding reflexes''' may allow urinary retention states to be improved