See Also: musculus sphincter ani internus(medicine)
musculus thyroarytenoideus internus(medicine)
musculus obturator internus(medicine)
musculus vastus internus(medicine)
musculus intercostalis internus(medicine)
musculus rectus internus(medicine)
musculus pterygoideus internus(medicine)
musculus sphincter(medicine)
musculus sphincter vesicae(medicine)
musculus sphincter vaginae(medicine)

musculus sphincter ani internus (medicine)


musculus sphincter ani internus -->
internal anal sphincter
<anatomy> A smooth muscle ring, formed by an increase of the circular fibres of the rectum, situated at the upper end of the anal canal, internal to the outer voluntary external anal sphincter.

This sphincter is maximally-contracted when the rectal ampulla is at rest -empty or relaxed to accommodate a distending faecal mass. It is inhibited with filling of the ampulla, increased distension and peristalsis.

Synonym: musculus sphincter ani internus, internal sphincter muscle of anus.