Bulbospongiosus
Pelvis & Perineum · Trunk
The bulbospongiosus is a superficial perineal muscle that surrounds the erectile tissue at the root of the external genitalia, and its arrangement differs between the sexes. In males it arises from the perineal body and a median raphe over the bulb of the penis and inserts into the perineal membrane, the corpus spongiosum, and the dorsum of the penis. In females it arises from the perineal body and passes forward on either side of the vaginal orifice to insert into the dorsum of the clitoris and the pubic arch. Functionally, it compresses the bulb of the penis to expel the last drops of urine and semen and assists erection in males, while in females it constricts the vaginal orifice and contributes to clitoral erection. It is supplied by the perineal branch of the pudendal nerve (S2-S4).
Origin, Insertion, Action & Nerve
Origin
Perineal body and median raphe of the bulb of the penis (males); perineal body (females)
Insertion
Perineal membrane, corpus spongiosum and dorsum of the penis (males); dorsum of the clitoris and pubic arch (females)
Action
Compresses the urethral bulb to expel urine and semen (males); constricts the vaginal orifice (females)
Nerve
Perineal branch of the pudendal nerve (S2–S4)
Attachments explained
The Bulbospongiosus is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Perineal body and median raphe of the bulb of the penis (males); perineal body (females)
Insertion
Perineal membrane, corpus spongiosum and dorsum of the penis (males); dorsum of the clitoris and pubic arch (females)
Action & function
When the Bulbospongiosus contracts, it produces the following movements: Compresses the urethral bulb to expel urine and semen (males); constricts the vaginal orifice (females).
As part of the Pelvis & Perineum group of the Trunk, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Bulbospongiosus receives its nerve supply from the Perineal branch of the pudendal nerve (S2–S4). This nerve carries fibres from spinal segment(s) S2, S4.
Because a muscle can only contract when its nerve is intact, injury to the Perineal branch of the pudendal nerve or to its spinal roots (S2, S4) can weaken or paralyse the Bulbospongiosus, impairing the movements it normally produces (compresses the urethral bulb to expel urine and semen (males)). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Bulbospongiosus (the OIANS method)
Learn bulbospongiosus by its relationship to the midline erectile tissue: in males it hugs the bulb of the penis, in females it flanks the vaginal opening, but in both it arises from the perineal body and squeezes what lies beneath it. Deriving its actions from that grip, emptying the urethra and aiding erection in males, constricting the orifice in females, is far more durable than memorising separate lists.
Pair it with ischiocavernosus, its neighbour in the superficial perineal pouch, since both share the perineal branch of the pudendal nerve and both aid erection by compressing erectile tissue. The clean division of labour, ischiocavernosus on the crus and bulbospongiosus on the bulb, is a reliable way to keep the two apart on exams.
Frequently asked questions
Where is the Bulbospongiosus located?
The Bulbospongiosus is a muscle of the Pelvis & Perineum group, located in the Trunk.
What is the origin of the Bulbospongiosus?
Perineal body and median raphe of the bulb of the penis (males); perineal body (females)
What is the insertion of the Bulbospongiosus?
Perineal membrane, corpus spongiosum and dorsum of the penis (males); dorsum of the clitoris and pubic arch (females)
What movements does the Bulbospongiosus produce?
Compresses the urethral bulb to expel urine and semen (males); constricts the vaginal orifice (females)
What nerve supplies the Bulbospongiosus?
Perineal branch of the pudendal nerve (S2–S4)
Is the Bulbospongiosus free to study in OIANS?
The Bulbospongiosus is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Trunk is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
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