The internal anal sphincter, IAS, (or sphincter ani internus) is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal; its inferior border is in contact with, but quite separate from, the external anal sphincter.

Is the anus smooth inside?

anal canal Thus, the internal sphincter is composed of smooth muscle and is innervated by the autonomic nervous system, while the external sphincters are of striated muscle and have somatic (voluntary) innervation provided by nerves called the pudendal nerves.

Why do I have a little lump in my anus?

If anything causes irritation, a blockage, or an infection, lumps may form on the anus that can make it feel hard. If a person notices a hard lump or a hardened anus, they should talk to their doctor and have the area examined. Most lumps are not a cause for concern.