Voluntary control of the external anal sphincter (EAS) plays an essential role in maintaining fecal continence, or the ability to retain the body's waste material until the time for proper discharge. This sphincter, known by a more common -- and sometimes less complimentary -- name, is comprised of deep, superficial, and subcutaneous striated muscle groups located around the boundary of the gastrointestinal tract. Innervation to this sphincter is provided by the somatic fibers of the second, third, and fourth sacral routes through nerves associated with genitalia.
Despite the considerable information existing about the peripheral and reflex control of the EAS, there are sparse data about the central control of voluntary contraction of this sphincter in humans. What is known mostly addresses its contraction response to experimental electrical or magnetic stimulation of the motor cortex, the region of the cerebral cortex most nearly immediately influencing movements of the face, neck and trunk, and arm and leg. Past studies have shown that the contracting of the EAS or pelvic floor to direct stimulation of the motor cortex, the cerebral cortical activity map related to voluntary contraction of this sphincter, could be quite different from the cortical topography of its control determined by direct stimulation of the cerebral cortex.
A New Study
To obtain a better understanding of the cortical control of the continence mechanism a new study attempted to determine the areas of the human
Contact: Donna Krupa
American Physiological Society