Pelvis - Pelvic Viscera (2)

Question 1

Describe the internal anal sphincter: location, structure, function.

Answer 1

Made of smooth muscle, involuntary, circular orientation of fibres, surrounds the superior two thirds of the anal canal. Contraction is stimulated by sympathetic supply, and inhibited by parasympathetic supply.

Question 2

Describe the external anal sphincer: location, structure, function.

Answer 2

Made of skeletal muscle, voluntary, circular orientation of fibres, attaches posteriorly to the coccyx. 3 parts: deep, superficial, subcutaneous. Supplied by S4.