Gastric Motility Lecture 29 . In addition to the longitudinal and circular components of the muscularis externa , there is present an oblique layer overlying the submucosa. Receptive relaxation occurs only in the Fundus and the upper Corpus . Though some passive stretch may occur, receptive relaxation is, at least in part, due to a centrally mediated reflex, initiated by swallowing, and resulting in inhibition of tonic contraction in the stomach wall , and consequent increase in intragastric volume . Receptive relaxation is a largely vagally mediated reflex.
Receptive relaxation is one of the deglutition reflexes .
These result from a series of local reflexes integrated within the ENS, involving interaction of longitudinal and circular muscle, modulated by ANS and gut hormones. Mechanism Regulating Motility -Motor activity in the distal stomach and in the intestinal tract is dictated by electrical phenomena arising in the smooth muscle itself. In the distal stomach , smooth muscle cells show a RMP of about 60 mV, outside positive. The frequency, number, and amplitude of response potentials in an ERA burst, will determine the strength and duration of contractions. Although for many years the dogma had been that the BER is generated by pacemaker cells in the longitudinal fibres and spreads electrotonically into the circular layer, recent evidence suggests that it may originate in the non-neuronal Interstitial Cells of Cajal , between the two layers of muscle, and spreads in both directions.