CENTRAL NERVOUS SYSTEM CONTROL OF MICTURITION, URINE STORAGE, AND VOIDING
The intent of this chapter is to review the current guidelines for the management of neurogenic bladder dysfunction. For an in-depth review of the anatomy and pathophysiology of the genitourinary system, please see Chapter 5. For a review of common medications used in the treatment of neurogenic bladder and bowel, please see Chapter 55.
The lower urinary tract has two main functions, storage and periodic elimination of urine, which are mediated by a central nervous system (CNS) and the spinal cord. Intracerebral and intrathecal injections of the drugs indicate that the micturition reflex pathways may pass through multiple relay stations in the brainstem and be modulated by inputs from various centers in the brain.1 The cholinergic agonists are known to act on centers in pons and medulla to facilitate micturition. Cortical and pontine regions that modulate voiding include the pontine micturition center (PMC), periaqueductal gray (PAG), thalamus, insula, anterior cingulate gyrus, and prefrontal cortices. The PMC and the PAG are thought to play a key role in the supraspinal control of continence and voiding.2 The anterior cingulate gyrus and insula possibly process autonomic arousal, visceral storage, and sensation.3 Several neurotransmitters including gamma-aminobutyric acid (GABA), opioids, peptides, and glutamic acid appear to have a role in the central pathways controlling micturition. The frontal cortex is crucial for decision making for micturition in an emotional and social context. The influence of these centers on the PMC is mediated primarily via the PAG, which also integrates bladder sensory information, thereby moderating coordinated voiding and storage of urine. CNS lesions below the PMC are associated with detrusor sphincter dyssenergia (Fig. 51–1). Intracranial lesions (e.g., head injuries, dementia, and tumors) and other conditions such as parkinsonism are usually associated with detrusor hyperreflexia. Possible causes of urge incontinence include dysfunction of the prefrontal cortex or limbic system.2
Detrusor sphincter dyssenergia occurs in CNS lesions below the level of the pontine micturition center.
BLADDER AND BOWEL INNERVATION
Neural control of the pelvic organ is through somatic and autonomic nervous systems and is well integrated via lumber sacral reflexes (see Fig. 51–1). Central representation of bladder and colon has been demonstrated by dual transsynaptic tracing in the rat.3 These analyses have demonstrated that Barrington's nucleus (three neuronal populations) is synaptically linked to both the bladder and the bowel.
These anatomic substrates underlie the central coordination of bladder and colon function and play a role in disorders characterized by a coexistence of bladder and colonic symptoms. Dysfunctions in this circuit may underlie the coexistence of colon and bladder symptoms observed in functional bowel disorders.
Parasympathetic motor innervations to the bladder wall and rectosigmoid are through the sacral 2, 3, ...