Myenteric Plexus

Structure/Morphology

The myenteric (Auerbach’s) plexus is a network of thin bundles of axons and neurons, which may be grouped as small ganglionic clusters. It lies within the muscular layer. The myenteric plexus arises from the periarterial plexus that follows the superior and inferior mesenteric arteries and their terminal branches. All components of the myenteric plexus are continuous with the inner circular muscle nerve fiber bundles, which go on to synapse with the ganglionic and non-ganglionic plexuses of the submucosa. Both the submucosal and the myenteric plexuses make up the enteric (or intrinsic) nervous system.

The enteric nervous system is unique to the digestive system and is autonomic in nature. It extends the entire length of the gastrointestinal tract and is composed of three types of neurons (Standring, 2016).

—Sensory neurons transmit information from receptors in the mucosa and muscle of the gut wall, which respond to mechanical, chemical, thermal, and osmotic stimuli. They project information to the interneurons.

—Motor neurons control the motility and secretions in the gut and are inhibitory or excitatory.

—Interneurons go between the sensory and motor neurons, thus integrating the information between the two.

The enteric nervous system may function autonomously; however, it does communicate with the central nervous system via parasympathetic and sympathetic fibers. Cross connections between the two allow for information from the gut to be relayed to the CNS, and vice versa. In general, sympathetic inputs cause inhibition of secretions and motor activity and contraction of sphincters and blood vessels (fight or flight response). Parasympathetic stimulation of the enteric nervous system promotes secretions and motor activity and dilation of the sphincters and blood vessels (rest and digest response) (Standring, 2016; Costa, Brookes and Hennig, 2000).

The interstitial cells of Cajal are flat, thin, branched cells are linked to the smooth muscle cells via gap junctions. They overlap with the myenteric plexus, and they are believed to act as pacemakers for myogenic contraction of the muscular layer, modulating the electrical slow wave activity to alter the rhythm of bowel contractions.

Anatomical Relations

The myenteric plexus is situated between the two muscular layers; superjacent to the inner circular smooth muscle layer and subjacent to the outer longitudinal smooth muscle layer.

Function

The myenteric plexus houses most of the enteric neurons with motor function. These act on the different effector cells within the intestinal system. In conjunction with the interstitial cells of Cajal, this enables the coordinated muscular movements of the colon, as well contributing to associated immune and endocrine functions (Standring, 2016).

List of Clinical Correlates

—Hirschsprung’s disease

References

Costa, M., Brookes, S. J. and Hennig, G. W. (2000) 'Anatomy and physiology of the enteric nervous system', Gut, 47 Suppl 4(Suppl 4), pp. iv15-iv26.

Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edition edn.: Elsevier Limited.