Anal Canal: Sphincters

Question 1

Anal sphincters

Answer 1

1. Internal
2. External

Question 2

Internal

Answer 2

1. Formed by thickened inner circular muscle layer
2. Surrounds anal canal upper 3/4
3. Formed of involuntary smooth muscle fibers and supplied by autonomic nerve fibers

Question 3

External

Answer 3

1. Lies outside internal anal sphincter
2. Surrounds whole anal canal
3. Formed of voluntary striated muscle fibers and has 3 parts
4. Supplied by somatic nerves from inferior rectal nerve (branch from pudendal nerve) and perineal branch of 4th sacral nerve

Question 4

Parts

Answer 4

1. Subcutaneous
2. Superficial
3. Deep

Question 5

Subcutaneous part

Answer 5

Surrounds anal canal lower 1/4 and anal orifice

Question 6

Superficial part

Answer 6

1. Superior to subcutaneous part
2. Only part with bony attachment
3. Extends from coccyx tip of behind to perineal body in front

Question 7

Deep part

Answer 7

1. Strongest part
2. Superior to superficial part
3. Surrounds canal upper part
4. Its deep fibers are reinforced by levator ani puborectalis part both parts blend with internal anal sphincter forming strong anorectal ring