Does the Internal Anal Sphincter Contribute to Pressure During Sexual Arousal or Ejaculation?
No, the internal anal sphincter (IAS) does not contribute to pressure associated with sexual arousal or ejaculation—the IAS is an involuntary smooth muscle ring that maintains resting anal tone for fecal continence, not sexual function. 1, 2
Physiologic Role of the Internal Anal Sphincter
The IAS serves a single, well-defined function in anorectal physiology:
The IAS is the major contributor to resting anal pressure (approximately 70-80% of baseline anal canal tone), functioning continuously and involuntarily to prevent passive leakage of stool and flatus. 1, 3, 2
The IAS generates spontaneous myogenic tone through smooth muscle contraction, modulated by autonomic nervous system input (sympathetic excitation increases tone, parasympathetic inhibition decreases tone). 2, 4
Resting anal pressure in healthy individuals averages 73 ± 27 cm H₂O, with the IAS responsible for the majority of this baseline pressure. 5
Why the IAS Does Not Participate in Sexual Function
The IAS operates independently of voluntary control and sexual arousal mechanisms:
The IAS maintains constant involuntary tone that is unrelated to sexual stimulation, arousal, or ejaculation—its function is purely to prevent fecal incontinence at rest. 1, 2
Sexual arousal and ejaculation involve voluntary pelvic floor muscle contraction (external anal sphincter, puborectalis, bulbospongiosus) coordinated through somatic pudendal nerve pathways (S2-S4), not the autonomic pathways controlling the IAS. 6
The external anal sphincter (EAS), not the IAS, is the voluntary striated muscle component that can be consciously contracted during sexual activity, but this is distinct from ejaculatory physiology. 6, 7
Autonomic Innervation Confirms Functional Separation
The nerve supply to the IAS is designed exclusively for continence regulation:
The IAS receives extrinsic autonomic innervation from the pelvic plexus via nerve fibers that run anterolaterally to the rectum and enter the intersphincteric space, modulating smooth muscle tone for fecal continence only. 4
Sympathetic input (via hypogastric nerves) increases IAS tone to maintain continence, while parasympathetic input (via pelvic nerves) mediates the rectoanal inhibitory reflex that allows rectal distension to trigger IAS relaxation for defecation. 8, 2
Neither of these autonomic pathways has any documented role in sexual arousal or ejaculatory pressure generation. 2, 4
Clinical Context: When IAS Dysfunction Matters
Understanding IAS function is critical only in the context of fecal continence disorders:
Reduced IAS tone (from structural injury, neurogenic dysfunction, or surgical sphincterotomy) results in passive fecal incontinence—leakage of stool and flatus at rest without awareness. 1, 3, 2
Patients with diabetes mellitus or Parkinson's disease commonly develop secondary visceral neuropathy affecting autonomic nerves to the IAS, leading to reduced resting tone and incontinence, not sexual dysfunction. 8, 6
Post-surgical IAS dysfunction (after lateral internal sphincterotomy for anal fissure) may cause minor flatus incontinence in 1-10% of patients, but sexual dysfunction after such procedures is neuropathic/myofascial (involving the external sphincter and pelvic floor muscles), not related to IAS pressure changes. 9
Common Pitfall to Avoid
- Do not conflate pelvic floor muscle tension during sexual activity with IAS function—voluntary pelvic floor contraction during arousal or orgasm involves the EAS and puborectalis (somatic innervation via pudendal nerve), while the IAS remains in its baseline involuntary resting state throughout sexual activity. 6, 7