Neural Control of Muscular Tone Determines Minuteto Minute Volume and Pressure in the Gastric Reservoir

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The gastric reservoir has two primary functions. One is to accommodate the arrival of a meal, without a significant increase in intragastric pressure and distension of the gastric wall. Failure of this mechanism can lead to the uncomfortable sensations of bloating, epigastric pain, and nausea. The second function is to maintain a constant compressive force on the contents of the reservoir. This pushes the contents into motor activity of 3 cycles/min for the antral pump. Drugs that relax the musculature of the gastric reservoir neutralize this function and suppress gastric emptying.

The musculature of the gastric reservoir is innervated by both excitatory and inhibitory motor neurons of the ENS. The motor neurons are controlled by the efferent vagus nerves and intramural microcircuits of the ENS. They function to adjust the volume and pressure of the reservoir to the amount of solid and/or liquid present while maintaining constant compressive forces on the contents. Continuous adjustments in the volume and pressure within the reservoir are required during both the ingestion and the emptying of a meal.

Increased activity of excitatory motor neurons, in coordination with decreased activity of inhibitory motor neurons, results in increased contractile tone in the reservoir, a decrease in its volume, and an increase in intraluminal pressure (Fig. 26.27). Increased activity of inhibitory motor neurons in coordination with decreased activity of excitatory motor neurons results in decreased contractile tone in the reservoir, expansion of its volume, and a decrease in in-traluminal pressure.

Increased Intragastric Pressure

^MUREHHS^ Muscular tone in the gastric reservoir.

^tmmmtl^mmm^ Tonic contraction of the musculature decreases the volume and exerts pressure on the contents. Tonic relaxation of the musculature expands the volume of the gastric reservoir. Neural mechanisms of feedback control determine intramural contractile tone in the reservoir.

^MUREHHS^ Muscular tone in the gastric reservoir.

^tmmmtl^mmm^ Tonic contraction of the musculature decreases the volume and exerts pressure on the contents. Tonic relaxation of the musculature expands the volume of the gastric reservoir. Neural mechanisms of feedback control determine intramural contractile tone in the reservoir.

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