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External anal sphincter: anatomy, location and function

A ring of voluntary skeletal muscle surrounding the anal canal. Keeps the anal canal closed and provides voluntary control of defecation.

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Structures

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Highlighted in the model: External anal sphincter. Click any part to read about it, or switch off “Highlight topic” to see the whole body. 3D data: BodyParts3D, © The Database Center for Life Science, CC BY 4.0; meshes simplified and recoloured. The model is an adult male.

External anal sphincter at a glance

What it is
A ring of voluntary skeletal muscle surrounding the anal canal.
Location
Surrounds the lower anal canal, attached to the perineal body in front and the anococcygeal ligament behind.
Function
Keeps the anal canal closed and provides voluntary control of defecation.
Body system
Muscular · single, midline structure
FMA ID
FMA21930 (Foundational Model of Anatomy)

Key facts

  • Innervation: inferior rectal (anal) nerve, a branch of the pudendal nerve (S2–S4)
  • Blood supply: inferior rectal artery

Clinical relevance

Damage during childbirth can cause fecal incontinence.

Structures next to the external anal sphincter

The nearest named structures in the 3D model, measured from the centre of each part:

References

  1. Foundational Model of Anatomy: External anal sphincter (FMA21930). EMBL-EBI Ontology Lookup Service.
  2. OpenStax. Anatomy and Physiology 2e, §11.2 Naming Skeletal Muscles. Rice University, 2022.
  3. Mitsuhashi N. et al. (2009). BodyParts3D: 3D structure database for anatomical concepts. Nucleic Acids Research 37, D782–D785. Data © The Database Center for Life Science, CC BY 4.0.

Related anatomy

Explore the whole body in the interactive 3D human anatomy model, or browse the A–Z list of human structures.