Bulbospongiosus !

The bulbospongiosus is a thin muscle on each side of the vaginal opening; it narrows the opening and helps the clitoris become erect.

Official name: Bulbospongiosus muscle

See in 3D →

Opens in the Durgical app, no sign-up needed.

What it is

A muscle that wraps the bulb of the penis; its two halves join in the midline.

What it does

Empties the last drops of urine from the urethra, helps with erection and pushes semen out at ejaculation.

Key facts

Origin: Perineal body
Insertion: Around the vaginal orifice over the vestibular bulbs to the perineal membrane and the body of the clitoris
Action: Constricts the vaginal orifice; compresses the vestibular bulbs and the greater vestibular gland; aids clitoral erection
Nerve: Perineal branch of pudendal nerve (S2–S4)
Blood supply: Perineal branch of internal pudendal artery

Relations

Deep: The vestibular bulb, with the Bartholin gland at its posterior end (male: the bulb of the penis)
Medial: The vaginal orifice and the vestibule
Lateral: The ischiocavernosus over the crus of the clitoris
Behind: The perineal body, where it blends with the external anal sphincter and the transverse perineal muscles
Superficial: Colles fascia and the fat of the labium majus

How to find it

Not seen as a separate muscle on examination; in dissection, after Colles fascia is removed, it is the thin sheet curving around the vaginal orifice over the vestibular bulb.

Examination

Bulbocavernosus reflex: squeezing the glans of the clitoris or penis (or tugging a urinary catheter) makes the anal sphincter contract; it tests S2–S4, and its return marks the end of spinal shock

On imaging

Not assessed on radiographs. On axial and coronal MRI of the perineum it is a thin muscle curving over the vestibular bulb on each side of the vaginal opening. It is seldom reported on its own: MRI and transperineal ultrasound are used to study the perineum after birth injury, a Bartholin cyst at its back end, and masses or congenital anomalies of the vulva.

Common problems

Straddle injuries (falling astride a bar or a beam) can bruise the perineum and tear the urethra.
Perineal pain or numbness, for example from long cycling.

How it is diagnosed

Examination; ultrasound or MRI when needed.

Treatment

Depends on the cause: rest, a better bicycle seat, or treatment of a urethral injury by a urologist.

Clinical notes

Torn in second-degree tears and cut in an episiotomy; its ends are brought together to rebuild the perineal body
Involuntary tightening of the muscles around the vaginal opening, this one included, is part of genito-pelvic pain disorders (formerly vaginismus)
Male: a straddle fall crushes the bulbar urethra against the pubis beneath this muscle

Development

Its shape follows the external genitalia: in the male the urethral folds fuse in the midline, leaving the raphe, and the two halves of the muscle meet over the bulb; in the female the folds stay apart as the labia minora and the muscle stays split around the vestibule.

Test yourself

Think of the answer, then tap the question to see it.

How is the bulbospongiosus arranged in the female compared with the male?

Female: two halves separated by the vaginal orifice, over the vestibular bulbs. Male: halves joined in a midline raphe over the bulb of the penis.

What does the bulbocavernosus reflex test, and how is it elicited?

S2–S4: squeezing the glans of the clitoris or penis (or tugging a catheter) makes the anal sphincter contract; its return marks the end of spinal shock.

In which perineal injuries is the bulbospongiosus torn or cut?

Second-degree tears and episiotomy; its ends are brought together to rebuild the perineal body.

Add to my cards (3)

Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): musculus bulbospongiosus TA2 2418
Official Spanish (DeCS): Músculo bulboesponjoso
English (TA2): Bulbospongiosus muscle
Also called: musculus bulbocavernosus

Sources: Terminologia Anatomica (TA2); Anatomy, Abdomen and Pelvis: Superficial Perineal Space.

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.