muscles of the pelvic floor and perineum: support of abdominopelvic organs

levator ani

broad, thin, tripartite muscle (pubococcygeus, puborectalis, and iliococcygeus parts); its fibers extend inferomedially, forming a muscular "sling" around male prostate (or female vagina), urethra, and anorectal junction before meeting in the median plane (O): extensive linear origin inside pelvis from pubis to ischial spine (I): inner surface of coccyx, levator ani of opposite side, and (in part) into the structures that penetrate it. action: supports and maintains position of pelvic viscera; resists downward thrusts that accompany rises in intrapelvic pressure during coughing, vomiting, and expulsive efforts of abdominal muscles; forms sphincters at anorectal junction and vagina; lifts anal canal during defecation nerve supply: s4 and inferior rectal nerve (branch of pudendal nerve)

bulbospongiosus

encloses base of penis (bulb) in males and lies deep to labia in females (O): central tendon of perineum and midline raphe of penis (I): anteriorly into corpus cavernosa of penis or clitoris acton: empties male urethra; assists in erection of penis and of clitoris nerve supply: pudendal nerve

external urethral sphincter

muscle encircling urethra and vagina (female) (O): ischiopubic rami (I): midline raphie action: constricts urethra; helps support pelvic organs nerve supply: pudendal nerve

superficial transverse perineal muscles

paired muscle bands posterior to urethral (and in females, vaginal) opening; variable; sometimes absent (O): ischial tuberosity (I): central tendon of perineum stabilizes and strengthens middle tendon of perineum nerve supply: pudendal nerve

ischiocavernosus

runs from pelvis to base of penis to base or clitoris (O): ischial tuberosities (I): crus of corpus cavernosa of male penis or female clitoris action: retards venous drainage and maintains erection of penis or clitoris nerve supply: pudendal nerve

coccygeus

small triangular muscle lying posterior to levator any; forms posterior part of pelvic diaphragm (O): spine of ischium (I): sacrum and coccyx action: supports pelvic viscera; supports coccyx and pulls it forward after it has been reflected posteriorly by defecation and childbirth nerve supply: s4 and s5

deep transverse perineal

together the pair spans distance between ischial rami; in females, lies posterior to the vagina (O): ischial rami (I): midline central tendon of perineum; some fibers into vaginal wall in females action: supports pelvic organs; steadies central tendon nerve supply: pudendal nerve