27.4 : Nerve Supply of the GI Tract

The neuronal supply to the gastrointestinal (GI) tract is essential for regulating various functions, including digestion, absorption, and movement of food. This intricate network of nerves is known as the enteric nervous system (ENS), often referred to as the "second brain" of the body.

The enteric nervous system consists of two major plexuses: the myenteric plexus (Auerbach's plexus) and the submucosal plexus (Meissner's plexus). These plexuses are located within the layers of the GI tract and play distinct roles in coordinating GI function.

The myenteric plexus is found between the longitudinal and circular muscle layers of the muscularis externa. It spans the entire length of the GI tract, from the esophagus to the anus. This plexus primarily controls the motility of the GI tract, regulating the contraction and relaxation of the smooth muscles. It coordinates peristalsis, the wave-like movement that propels food along the digestive tract. Additionally, the myenteric plexus controls the opening and closing of the sphincters, which regulate the passage of food through different parts of the GI tract.

On the other hand, the submucosal plexus lies within the submucosa layer of the GI tract, beneath the mucosal lining. Except for the stomach, it is present throughout the GI tract but is more concentrated in certain regions such as the small intestine. The submucosal plexus controls secretory functions and blood flow in the GI tract. It regulates the secretion of enzymes, acids, and hormones necessary for digestion and nutrient absorption. This plexus also plays a role in modulating local blood flow, ensuring adequate oxygen and nutrient supply to the surrounding tissues.

Both the myenteric and submucosal plexuses are part of the ENS, which is composed of millions of neurons that communicate with each other and with the central nervous system (CNS). These neurons integrate sensory information from the GI tract, process it, and generate motor responses to maintain homeostasis.

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, which form the complex network within the GI tract.

In summary, the neuronal supply to the gastrointestinal tract is facilitated by the enteric nervous system, which comprises the myenteric and submucosal plexuses. The myenteric plexus controls GI motility, while the submucosal plexus regulates secretory functions and blood flow. Together, these plexuses play a vital role in maintaining the proper functioning of the digestive system.