Neurophysiology & Pharmacology of the Lower Urinary Tract
The lower urinary tract does two opposite jobs — store urine quietly and then empty it completely on command — and switching cleanly between them requires precise neural coordination.
The big picture
The lower urinary tract does two opposite jobs — store urine quietly and then empty it completely on command — and switching cleanly between them requires precise neural coordination. Almost every voiding disorder, and every drug used to treat one, makes sense once you know the three nerves, their transmitters and receptors, and which mode each promotes. This chapter is the wiring diagram behind incontinence, retention, and the drugs that treat them.
The framework: three pathways (parasympathetic, sympathetic, somatic), the storage-versus-emptying switch (coordinated by the pons), and the receptor pharmacology that lets you push the system either way.
Mechanism pathway
Tap any step to see why it happens.
Interactive — the micturition reflex (storage vs voiding)
Diagnostic algorithm
Each step answers one question. Tap to expand.
Board traps
Parasympathetic (pelvic, S2–S4, ACh→M3) = empty (detrusor contraction).
Sympathetic (hypogastric, β-3 detrusor relaxation + α bladder-neck contraction) = store.
Somatic (pudendal) = voluntary external sphincter.
Antimuscarinics and β-3 agonists treat storage (overactive bladder); α-blockers treat outlet obstruction.
The pons coordinates the storage/emptying switch — its disruption causes dyssynergia.