Which layer(s) of the alimentary canal wall house a nerve plexus? A. serosa & muscularis externa B. submucosa & mucosa C. muscularis mucosa & submucosa D. lamina propria & muscularis mucosa E. muscularis externa & submucosa
The correct answer and explanation is:
The correct answer is E. muscularis externa & submucosa.
Explanation:
The alimentary canal, which includes the digestive tract, is composed of several layers. These layers are the mucosa, submucosa, muscularis externa, and serosa. Among these, two key layers house nerve plexuses that play an important role in the regulation of gastrointestinal functions.
- Muscularis externa: This layer is primarily made up of smooth muscle, which is responsible for peristalsis, the rhythmic contraction and relaxation that moves food along the digestive tract. The muscularis externa contains the myenteric plexus (also called the Auerbach’s plexus), which lies between the circular and longitudinal muscle layers. This nerve plexus is involved in controlling the motility of the gastrointestinal tract. It is critical for coordinating the muscle contractions that propel food through the digestive system.
- Submucosa: The submucosa lies just beneath the mucosa and contains blood vessels, lymphatics, and nerves. Within the submucosa, there is another nerve plexus known as the submucosal plexus (also called Meissner’s plexus). This plexus is primarily involved in regulating the secretion of digestive enzymes and fluids. It also plays a role in controlling blood flow to the digestive tract and coordinating local motility of the mucosa.
These two nerve plexuses, the myenteric plexus in the muscularis externa and the submucosal plexus in the submucosa, form the enteric nervous system (ENS), often referred to as the “second brain.” They operate independently of the central nervous system but can still be influenced by signals from the brain and spinal cord. The ENS controls many aspects of digestion, including motility, secretion, and blood flow, ensuring that the digestive process runs smoothly.
In summary, the correct answer is E because both the muscularis externa and submucosa contain important nerve plexuses involved in regulating the function of the digestive system.