The enteric nervous system (ENS) is a subdivision of the autonomic nervous system (ANS) that directly controls the gastrointestinal system.
The gastrointestinal (GI) system has its nervous system, the enteric nervous system (ENS) which is a branch of the autonomic nervous system operating independently of the brain and the spinal cord. The enteric nervous system is embedded in the lining of the gastrointestinal system as a mesh of neurons.
The neurons of the ENS are classed into two types: The myenteric plexus which is located between the inner and outer layers of the muscular tissue controls the velocity and intensity of its contractions controlling the motility throughout the whole gut. Inhibition of the myenteric plexus helps to relax the sphincters allowing food to pass between organs. The second type of neuron is the submucosal plexus which controls local secretion and absorption, as well as local muscle movements.
The enteric nervous system includes efferent neurons, afferent neurons, and interneurons, all of which make the enteric nervous system capable of carrying reflexes and acting as an integrating center in the absence of CNS input. For instance, the sensory neurons report mechanical and chemical conditions, while the motor neurons control peristalsis and the churning of intestinal contents through the intestinal muscles. Other neurons control the secretion of enzymes.
The parasympathetic nervous system can stimulate the enteric nerves to increase the enteric function. The parasympathetic enteric neurons function in defecation and provide a rich nerve supply to the sigmoid colon, the rectum, and the anus. Conversely, stimulation of the enteric nerves by the sympathetic nervous system will inhibit enteric function and capabilities.
Practice Questions
Khan Academy
Spinal nerves and Guillain-Barre syndrome
MCAT Official Prep (AAMC)
Key Points
• The enteric nervous system (ENS), which is embedded in the lining of the gastrointestinal system, can operate independently of the brain and the spinal cord.
• The ENS consists of two plexuses, the submucosal and the myenteric. The myenteric plexus increases the tone of the gut and the velocity and intensity of contractions. The submucosal plexus is involved with local conditions and controls local secretion, absorption, and muscle movements.
• While described as a second brain, the enteric nervous system normally communicates with the central nervous system (CNS) through the parasympathetic (via the vagus nerve ) and sympathetic (via the prevertebral ganglia) nervous systems. However, it can still function when the vagus nerve is severed.
• The ENS includes efferent neurons, afferent neurons, and interneurons, all of which make the ENS capable of carrying reflexes and acting as an integrating center in the absence of CNS input.
Key Terms
plexus: a branching network formed by nerves or blood vessels
enteric nervous system: one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract
autonomic nervous system: the nervous system that acts largely unconsciously and regulates bodily functions
sphincter: a circular muscle that controls opening at the junction of two parts
myenteric plexus: the major nerve supply to the gastrointestinal tract and controls GI tract motility
submucosal plexus: a nerve bundle that controls glandular secretions, alters electrolyte and water transport and regulates local blood flow in the GI tract
peristalsis: contraction in the smooth muscle of the esophagus that helps in the transport of food
parasympathetic nervous system: the nervous system that conserves energy as it slows the heart rate, increases intestinal and gland activity and relaxes sphincter muscles in the gastrointestinal tract
sympathetic nervous system: the nervous system that directs the body’s rapid involuntary response to dangerous or stressful situations
defecation: removal of feces from the body via the anus