Pelvic Floor Muscles and Sphincters During Erection and Ejaculation

Abstract

The pelvic floor muscles (puborectalis [PR], levator ani [LA]) and external anal (EAS) and urethral sphincters (EUS) were studied during erection and ejaculation in 12 mongrel dogs. The animals were anesthetized and the response of PR, LA, EAS, and EUS to electroejaculation (EE) was evaluated. Penile tumescence and rigidity as well as increase of the EMG activity of the aforementioned muscles and sphincters occurred. The rigidity and EMG activity increased as the voltage and current of EE continued to increase until ejaculation occurred at a mean voltage of 11.1 ± 1.2 V and current of 122.4 ± 14.4 mA. The increased PR activity might express the prostatic secretions into the posterior urethra. LA contraction seems to elevate the prostate and partially straightens the prostato-membraneous urethral kink that might occur during erection. The EAS and EUS contractions are believed to abort the urge to defecate or urinate and prevent leak of feces, flatus, or urine during coitus. The rhythmic EUS contraction at ejaculation might act as a “suction ejection pump,” sucking the genital fluid into the posterior urethra while being relaxed and ejecting it into the bulbous urethra upon contraction.

Key Words:

• ejaculation
• external anal sphincter
• external urethral sphincter
• levator ani
• puborectalis