Nerve Supply of the GI Tract

The enteric nervous system (ENS) is an intrinsic network of nerves in the gastrointestinal tract, often called the second brain. It comprises two major plexuses: the myenteric plexus, located between longitudinal and circular muscle layers, and the submucosal plexus, located within the submucosa. Both contain motor and sensory neurons and interneurons that regulate digestive functions.

The myenteric plexus primarily controls GI tract motility by regulating smooth muscle contraction and relaxation. It coordinates peristalsis, the wave-like movement that propels food through the digestive tract, and controls sphincter opening and closing. This plexus spans the entire length of the gastrointestinal tract from the esophagus to the anus.

The submucosal plexus controls secretory functions and local blood flow in the GI tract. It regulates secretion of enzymes, acids, and hormones necessary for digestion and nutrient absorption. This plexus is present throughout the GI tract except the stomach and is most concentrated in the small intestine.

Parasympathetic neurons from the vagus and pelvic splanchnic nerves synapse with neurons in both the myenteric and submucosal plexuses, as well as with smooth muscles and glands. These parasympathetic nerves stimulate the ENS and increase activities like GI secretions and peristalsis, promoting digestive function.

Sympathetic nerves originating from the thoracic and upper lumbar spinal cord synapse with neurons in the myenteric and submucosal plexuses. These nerves inhibit ENS neurons, reducing GI secretion and peristalsis. Emotional states like anger, fear, and anxiety can slow digestion through sympathetic nerve stimulation.

The myenteric plexus controls GI motility and food movement, while the submucosal plexus regulates secretory functions and blood flow. Together, these plexuses integrate sensory information from the GI tract and generate motor responses that maintain homeostasis and coordinate mechanical and chemical digestion in the small intestine.

The enteric nervous system originates from neural crest cells during embryonic development. These cells migrate along the gut tube, differentiating into neurons and glial cells that form the complex network within the GI tract. This developmental process establishes the intricate nerve plexuses that regulate digestive functions throughout life.