Question

Why is it necessary for the brain to interact with the stomach even though it is mostly an involuntary process?

Answer 1

Most information received by the brain about GI contents is transmitted via vagal afferent feedback signals. The vagus is one of two major extrinsic innervation sources, the other being the spinal cord (Sengupta, 2006). Spinal cord afferents appear to play more of a role in mediating GI pain than in providing feedback to the brain about nutrient contents, according to Moran.

three types of vagal afferent endings, each providing a different type of information to the brain: (1) intramuscular array (providing “stretch” information), (2) intraganglionic laminar endings (providing “tension” information), and (3) mucosal terminals (providing “nutrient” information). According to Moran, it has been fairly well demonstrated that intramuscular array terminals measure stretch; that is, as the stomach begins to fill and food enters the small intestine, the presence of that food causes a stretch in the surrounding muscle fibers that activates vagal afferent neurons with intramuscular array endings (Phillips and Powley, 2000). That activation is transmitted to the brain. The intraganglionic laminar endings, which are found primarily in the stomach and in the proximal duodenum, have been hypothesized to measure tension (Phillips and Powley, 2000). The difference between measuring stretch and measuring tension can be confusing, Moran remarked. Stretch is a change in volume, while tension is a change in the surrounding musculature with no change in volume. Many vagal afferents have both “stretch” and “tension” endings and are able to respond to both stimuli simultaneously. The third type of vagal afferent ending, the mucosal terminal, is located mainly in the intestine, with the endings in close proximity to where nutrients are being absorbed and where various kinds of endocrine cells are releasing their products. “Nutrient” vagal afferents respond to overall nutrient character, not load volume