Nervous system control of your bowel

Your gastrointestinal tract is controlled by your autonomic nervous system with sympathetic and parasympathetic nerves working in harmony. Nerves from the lower levels of your spinal cord control your sphincters.

Which nerves control what?

A complex series of nerves control your bowel.

Rectum and anal canal nerves

The smooth muscle of the rectum and anal canal is controlled by:

• parasympathetic nerves from the S2, S3 and S4 levels of the spinal cord, called thepelvic splanchnic nerve (this nerve stimulates your rectum and anal canal to contract or tighten, assisting in defecation)
• sympathetic nerves from the T11-L2 levels of your spinal cord, which form a nerve called thehypogastric nerve (this stimulates your rectum and anal canal to relax).

Internal anal sphincter nerves

Your internal anal sphincter is controlled by:

• parasympathetic nerves from the S2, S3 and S4 levels of the spinal cord (these cause your internal anal sphincter to relax, and this allows faeces to pass through the anus when your rectum and anal canal contract)
• sympathetic nerves from the T11-L2 levels of the spinal cord (these cause your sphincterto contractor tighten).

Your internal anal sphincter functions outside your conscious control. This is referred to as involuntary control, meaning that it operates in an automatic (reflex) manner.

External anal sphincter nerves

Your external anal sphincter is controlled by:

• spinal nerves from the S2, S3 and S4 levels of your spinal cord, which form the pudendal nerve.
• skeletal muscle, which can be voluntarily (consciously) controlled.