• Internal anal sphincter
  • External anal sphincter

MuscleActionOriginInsertionInnervationBlood supply
Internal anal sphincter Constricts anal canal (involuntary)- Muscular ring which surrounds anal canal- Muscular ring which surrounds anal canal- Parasympathetic fibres from S4- Middle rectal artery
External anal sphincterConstricts anal canal (voluntary)- Deep: Surrounds superior anal canal
- Superficial: Surrounds inferior anal canal
- Subcutaneous: surrounds anal aperture
- Deep: surrounds superior anal canal
- Superficial: Perineal body and coccyx
- Subcutaneous: surrounds anal aperture
- Pudendal nerve (S2 and S3)
- Inferior rectal nerve (S4)
- Inferior rectal artery