The 'enteric nervous system' ('ENS') is the part of the
nervous system that directly controls the
gastrointestinal system. It is capable of autonomous functions such as the coordination of
reflexes, although it receives considerable innervation from the
autonomic nervous system and thus is often considered a part of it. Its study is the focus of
neurogastroenterology. It has as many as one billion neurons, one hundredth of the number of neurons in the
brain, and considerably more than the number of neurons in the
spinal cord.
Layers
The neurons of the ENS are collected into two types of
ganglia:
myenteric (Auerbach's) and
submucosal (Meissner's) plexuses. Myenteric plexuses are located between the inner and outer layers of the
muscularis externa, while submucosal plexuses are located in the
submucosa.
Complexity
There are several reasons why the enteric nervous system may be regarded as a second brain. The enteric nervous system can operate autonomously. It normally communicates with the CNS through the
parasympathetic (eg, via the
vagus nerve) and
sympathetic (eg, via the
prevertebral ganglia) nervous systems. However,
vertebrate studies show that when the vagus nerve is severed, the enteric nervous system continues to function.
The complexity of the enteric nervous system is another reason for its status as a second brain. In vertebrates the enteric nervous system includes
efferent neurons,
afferent neurons, and
interneurons, all of which make the enteric nervous system capable of carrying reflexes in the absence of CNS input. The sensory neurons report on mechanical and chemical conditions. Through intestinal muscles, the motor neurons control
peristalsis and churning of intestinal contents. Other neurons control the secretion of
enzymes. The enteric nervous system also makes use of the same
neurotransmitters as the CNS, such as
acetylcholine,
dopamine, and
serotonin. The enteric nervous system has the capacity to alter its response depending on such factors as bulk and nutrient composition.
References
★ The book
The Second Brain by Dr.
Michael D. Gershon
★
"The Enteric nervous system (ENS)" at anaesthetist.com
★
Ageing of the enteric nervous system., Saffrey M, , , Mech Ageing Dev, 2004 Link
★
Enteric nervous system, Grundy D, Schemann M, , , Curr Opin Gastroenterol, 2006 Link
★ Furness JB (2006) The Enteric Nervous System. Blackwell, Oxford, pp 274
External links
★
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