What is the difference between the internal and external anal sphincters?
QUESTION: What is the difference between the internal and external anal sphincters?
External sphincter (puborectalis muscle)
– under CNS (voluntary control)
– inferior rectal branch of internal udendal nerve and perineal branch of S4
– is the continuation of the levator ani muscle (striated muscle)
– involuntary control
– is the continuation of the circular band of colon muscle (smooth muscle)
– is normally contracted
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Source: The Absite Review, p.223
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