Muscle
Internal urethral sphincter
Autonomic smooth muscle at the bladder outlet
High-yield
Sympathetic alpha-adrenergic activity increases bladder-neck and proximal urethral resistance. Coordinated reduction of outlet resistance accompanies detrusor contraction during voiding.
Overview
Smooth muscle around the bladder neck and proximal urethra contributes to the internal outlet mechanism. The male preprostatic region has an important role in directing semen forward during ejaculation. Female outlet closure relies on distributed smooth muscle and supporting tissues rather than an identical discrete ring.
Reference facts
- Origin
- Smooth-muscle bundles at the bladder neck blend with detrusor and proximal urethral muscle rather than forming a universally separable anatomical collar.
- Insertion
- Concentrated around the male preprostatic outlet; the female arrangement is less discretely ring-like.
- Innervation
- Hypogastric sympathetic pathways promote outlet tone; pelvic and local inhibitory pathways participate in relaxation during voiding.
- Action
- Supports urine storage and, in males, reduces backward passage of semen into the bladder during ejaculation.
- Blood supply
- Vesical and adjacent internal iliac branches, with vaginal contributions in females.
Clinical correlation
Bladder-neck surgery can impair forward ejaculation. Alpha-1 blockers may also cause ejaculatory changes, but tamsulosin-related absent or reduced ejaculate can reflect impaired seminal emission rather than retrograde ejaculation alone.
Frequently asked questions
What does the internal urethral sphincter do?
The internal urethral sphincter supports urine storage and, in males, reduces backward passage of semen into the bladder during ejaculation.
What nerve innervates the internal urethral sphincter?
Hypogastric sympathetic pathways promote outlet tone; pelvic and local inhibitory pathways participate in relaxation during voiding.
Where does the internal urethral sphincter attach?
Origin: Smooth-muscle bundles at the bladder neck blend with detrusor and proximal urethral muscle rather than forming a universally separable anatomical collar. Insertion: Concentrated around the male preprostatic outlet; the female arrangement is less discretely ring-like.
What is the blood supply of the internal urethral sphincter?
The internal urethral sphincter is supplied by the vesical and adjacent internal iliac branches, with vaginal contributions in females.