Musculus Sphincter Ani, also known as the anal sphincter muscle, is a circular muscle located at the opening of the anus. It is responsible for the controlled relaxation and contraction of the anal canal, playing a crucial role in the regulation of defecation.
The musculus sphincter ani consists of two main components: the internal anal sphincter and the external anal sphincter. The internal sphincter is an involuntary smooth muscle that lies closest to the inside of the rectum. It remains contracted most of the time, providing a baseline tone and maintaining faecal continence. This involuntary contraction helps prevent spontaneous passage of stool and gas.
The external anal sphincter, on the other hand, is a voluntary skeletal muscle that surrounds the inner internal sphincter. It allows for conscious control over the relaxation and contraction of the anal canal. This allows humans to delay or facilitate defecation as needed.
Together, the internal and external sphincters work in coordination to relax during defecation while ensuring fecal continence at other times. The internal sphincter relaxes when the rectum becomes distended with stool, sending signals to the brain to initiate the conscious relaxation of the external sphincter, thereby facilitating the passage of feces.
Disorders or damage to the musculus sphincter ani, such as anal sphincter dysfunction or injury, can lead to conditions like fecal incontinence (the inability to control bowel movements) or anal leakage. Various treatments, including medication, exercises, or surgical procedures, may be employed to address these conditions and restore normal sphincter function.
