Bulbospongiosus muscle

Origin and insertion

The attachments of bulbospongiosus are different among males and females. In males, the muscle consists of two parts that are fused at the median fibrous raphe of penis. In addition, the fibers originate from several surrounding structures; perineal body, superficial transverse perineal muscle and external anal sphincter. From the raphe, the fibers extend in the superolateral direction to attach to several structures of the penis;

• Posterior fibers fuse with the perineal membrane
• Central part of the muscle surrounds the bulb of penis and corpus cavernosum and ends by blending with dorsal surfaces of their respective fasciae
• Anterior part covers the sides of the corpora cavernosa, inserting to their dorsolateral sides and to the tendinous expansion that covers the dorsal vessels of the penis

In females, the two parts of the muscle are separate from each other. They both originate from the anterior surface of perineal body, after which they course on each side of the vagina. Both parts insert to the corpora cavernosa of clitoris.

Relations

In both sexes, the bulbospongiosus muscle is located in the superficial perineal space of perineum, anterior to the perineal body. In males, the muscle covers the bulb of penis and corpora cavernosa. In females, it is found on each side of vaginal orifice covering the bulbs of the vestibule.

Together with ischiocavernosus and superficial transverse perineal muscle, it comprises a triangular space filled with adipose tissue. Along with these two muscles, bulbospongiosus is invested within the deep perineal fascia (of Gallaudet).

Innervation

Bulbospongiosus is innervated by the deep branch of perineal nerve (S2-S4), which is a branch of the pudendal nerve.

Blood supply

Blood supply to bulbospongiosus comes from the internal pudendal artery, via its branch; the perineal artery.

Function

In males, the function of bulbospongiosus is to aid in emptying the penile urethra during urination and ejaculation. Together with the ischiocavernosus muscle, it compresses the bulb of penis and the deep dorsal vein of penis. This leads to the blockage of venous drainage from the penis, and consequential erection of the penis.

In females, it helps to empty the greater vestibular glands by constricting the vaginal orifice. The anterior fibers compress the deep dorsal vein of clitoris, facilitating the erection of this structure.