The Internal Anal Sphincter Has No Direct Role in Male Sexual Arousal or Orgasm
The internal anal sphincter (IAS) does not play a role in sexual buildup for males. The IAS is an involuntary smooth muscle primarily responsible for maintaining resting anal tone and fecal continence, not sexual function.
Anatomic and Physiologic Evidence
The muscles involved in male sexual response are distinct from the IAS:
The external anal sphincter (EAS) and bulbocavernosus muscle function as an integrated unit during sexual activity, not the IAS 1, 2. These muscles contract synchronously during erection and ejaculation, with the EAS helping to prevent defecation/urination during coitus and the bulbocavernosus acting as a "suction ejection pump" during ejaculation 1.
The pelvic floor muscles (puborectalis, levator ani) and external urethral sphincter are the active players in male sexual function 1. The puborectalis helps express prostatic secretions, while the levator ani elevates the prostate and straightens the prostato-membranous urethral angle during erection 1.
Pelvic floor muscle tone (hypotonicity or hypertonicity) affects sexual function, but this refers to the striated voluntary muscles, not the IAS 3. Hypertonus of pelvic floor muscles contributes to sexual pain disorders in men, but this involves the voluntary external sphincter complex 3.
Clinical Context
The IAS functions autonomously to maintain continence through smooth muscle tone. Studies of men engaging in receptive anal intercourse show decreased resting anal pressures (reflecting IAS function) but normal squeeze pressures (reflecting EAS function), with no complaints of sexual dysfunction 4. This demonstrates the IAS relaxes during anal penetration but plays no active role in sexual pleasure or arousal.
The anterior rectal wall and anal canal produce erogenous sensations during receptive anal intercourse, but these sensations arise from nerve endings and the prostate region, not from IAS contraction or activity 5, 6.
Common Pitfall
Do not confuse the IAS with the EAS or other pelvic floor muscles. The IAS is involuntary smooth muscle for continence; the EAS and associated striated muscles are the voluntary muscles involved in sexual response 2.