Micturition is a local spinal reflex, influenced by descending pathways from the brain. Stretch receptors in the bladder wall initiate the process. The reflex is a positive feedback reflex, with bladder emptying being completed once the reflex has become established. Central control resides in the nucleus coeruleus in the rostral pons.
• Parasympathetic innervation of the detrusor muscle (a meshwork of interlacing smooth muscle bundles forming three layers and behaving as a functional syncytium) from the intermediolateral grey column at S2-S4, via the preganglionic nervi erigentes.
• Sympathetic innervation of the bladder neck and proximal urethra from the intermediolateral column at T10-L2.
• Somatic innervation of the bladder, pelvic floor and urethra via the pudendal nerve (S2-S4).
• Conscious initiation at a socially acceptable time.
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