Various significant connections of the male pelvic floor muscles with special reference to the anal and urethral sphincter muscles

Abstract

The male pelvic floor is a complex structure formed by several muscles. The levator ani muscle and the perineal muscles are important components of the pelvic floor. The perineal muscles comprise the external anal sphincter, bulbospongiosus, superficial transverse perineal muscles, and ischiocavernosus. Although the connections of the muscles of the pelvic floor have been reported recently, the anatomical details of each muscle remain unclear. In this study, we examined the male pelvic floor to clarify the connection between the muscles related to function. Fifteen male pelvises were used for microscopic dissection, and three male pelvises were used for histological examination. On the lateral aspect, the perineal muscles were connected to each other. Bundles of the levator ani muscle extended to connect to the perineal muscles. In addition, the extended muscle bundle from the levator ani muscle and the perineal muscles surround the external urethral sphincter. On the medial aspect, the levator ani muscle and the external anal sphincter form the anterior and posterior muscular slings of the anal canal. The connection between the perineal muscles and levator ani muscle indicates a possible close relationship between the functions of the urethra and anus.

The series of smooth muscle structures in the pelvic floors of men: Dynamic coordination of smooth and skeletal muscles

“…However, we have perceived them as a series of smooth muscle structures continuous with the longitudinal muscle of the rectum and have demonstrated their continuity and spatial distribution (Muro et al, 2018). Furthermore, we have reported that this series is surrounded laterally by continuous skeletal muscles (Suriyut et al, 2020). The levator ani is continuous with the external anal sphincter in the anterior and posterior regions of the anal canal, as illustrated in Figure 8.…”

“…Although the pelvic floor muscles have generally been considered independent, we previously reported that the muscle bundles of the skeletal muscles are connected to each other in the male pelvic floor (Suriyut et al, 2020). This finding suggests that skeletal muscles of the pelvic floor such as the levator ani and perineal muscles act as a complex rather than independently.…”

“…The anatomy around the rectum and anal canal has attracted increased attention since the development of anorectal surgery (Aigner et al, 2004; Kraima et al, 2016, Tsukada et al, 2016; Nakajima et al, 2017; Muro, Tsukada, Harada, Ito, & Akita, 2018; Muro, Tsukada, Harada, Ito, & Akita, 2019; Okada et al, 2019). We previously analyzed the muscle structure around the rectum and anal canal anatomically (Baramee, Muro, Suriyut, Harada, & Akita, 2020; Kato, Muro, Kato, Miyasaka, & Akita, 2020; Muro et al, 2014; Muro et al, 2018; Muro et al, 2019; Muro et al, 2020; Nakajima et al, 2017; Suriyut, Muro, Baramee, Harada, & Akita, 2020; Tsukada et al, 2016). Those studies revealed a very interesting distribution of smooth muscle in this region.…”

Anatomy of Cowper’s gland in humans suggesting a secretion and emission mechanism facilitated by cooperation of striated and smooth muscles

“…Our research group has clarified that the external anal sphincter (EAS), superficial transverse perineal muscle (STP), and levator ani (LA) extend and surround the anterior and lateral sides of the urethra to form the EUS 12 . This means that the EUS is not an independent muscle, but a continuous structure with other pelvic floor muscles.…”

“…We have reported the characteristic structure of the pelvic floor, in which the striated muscles share their muscle bundles and are continuous, and the smooth muscle occupies the space between them [11][12][13][14][15][16][17][18][19][20] . These studies suggest that striated and smooth muscles coordinate in anal function and pelvic floor support.…”