Skip to Main Content






  • Detrusor: “Bladder muscle”—smooth muscle; innervation is parasympathetic (muscarinic acetylcholine—M2, M3; contraction) and sympathetic (β3-adrenergic receptors; detrusor inhibition or relaxation) (Figure 5-1)

  • Urethral sphincter

    • Internal urethral sphincter (IUS): Smooth muscle; sympathetic (α1) innervation; muscarinic acetylcholine, α- and β-adrenergic receptors

    • External urethral sphincter (EUS): Striated muscle; somatic motor innervation via pudendal nerve (S2–S4); nicotinic acetylcholine receptors

    • Submucosal endovascular cushions

    • Surrounding tissue support—hammock hypothesis—the anterior vaginal wall with its attachment to the arcus tendineus of the pelvic fascia forms a hammock of tissue under the urethra and bladder neck that prevents urethral and bladder neck descent, such that the urethra compresses shut with increased intra-abdominal pressure

Figure 5-1

Anteroposterior view of bladder anatomy. (Used with permission from Hoffman BL, Schorge JO, Schaffer JI, Halvorson LM, Bradshaw KD, Cunningham F, Calver LE. Chapter 23. Urinary incontinence. In: Hoffman BL, Schorge JO, Schaffer JI, Halvorson LM, Bradshaw KD, Cunningham F, Calver LE, eds. Williams Gynecology. 2nd ed. New York, NY: McGraw-Hill; 2012.)

Graphic Jump Location



  • Bladder filling = SYMPATHETIC = “STORAGE”

    • L1–L3 → lumbar sympathetic ganglia → forms hypogastric nerve to pelvis

    • Norepinephrine released → decreases smooth muscle tone in bladder

      • Relaxation of detrusor muscle: β3-adrenergic receptors in bladder stimulated (bladder fills)

      • Contraction of IUS: α-Adrenergic receptors in IUS stimulated (sphincter tightens)

      • Contraction of EUS by trained voluntary action (pudendal nerve originates from S2 to S4 to innervate EUS and perineal muscles—acetylcholine)

  • Micturition (emptying of bladder) = PARASYMPATHETIC = “PEEING”

    • Full bladder sensed by mechano-receptors in bladder

    • S2–S4 → sacral spinal cord → forms pelvic nerve

    • Stimulates bladder using acetylcholine and relaxes the urethra employing nitric oxide

      • Contraction of detrusor muscle: Muscarinic cholinergic (M3) receptors stimulated (bladder contracts)

      • Relaxation of IUS: M3 receptors stimulated (sphincter relaxes)

      • Relaxation of EUS by trained voluntary action (pudendal nerve originates from S2–S4—acetylcholine)






Involuntary loss of urine. Prevalence in the United States is about 50% of adult women.


  • Stress urinary incontinence (SUI): Most common type (50–70% of UI)

    • Involuntary leakage during effort, exertion, sneezing, or coughing

    • Risk factors include age, parity, vaginal delivery

    • Leakage with stress test. Bladder capacity and post-void residual (PVR) normal (PVR generally considered normal if <150 cc or <1/3 void volume)

    • Urethral hypermobility (straining angle ≥30 degrees on Q-tip test) present in many women with SUI

    • Urodynamic SUI: During filling cystometry, involuntary urine leakage with increased intra-abdominal pressure and without detrusor contraction

  • Urge incontinence

    • Leakage accompanied by or immediately preceded by urge to void

    • Typically results from sudden, involuntary detrusor contractions

    • Usually idiopathic; but can be from inflammation/irritation, calculi, neurologic disorders, outlet obstruction, increased urine output

    • Urodynamics: If detrusor contractions are seen on urodynamics, it is called Detrusor Overactivity (DO). Detrusor instability; ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.


About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.