Schematic structure of striated (A) and smooth muscle cells (B). C: the striated fibers receive innervations that release acetylcholine (ACh) from vesicles in synaptic clefts, and ACh receptors (AChR) are located on postsynaptic membrane. The AChR on striated muscle are ion channels, which initiate membrane depolarization when activated. This depolarization travels the sarcolemma and dives on T-tubules, reaching the dihydropyridine receptor (DHPR), which communicates with Ca2+ channels known as ryanodine receptors (RyR) to trigger Ca2+ efflux from sarcoplasmic reticulum (SR) to cytosol. D: neurons that stimulate smooth muscle cells possess varicosities where the vesicles are assembled. In this context, ACh diffuses to stimulate more than one single cell. The AChR on smooth muscle cells is coupled to G protein, which results in a production of second messengers. These second messengers are responsible for Ca2+ efflux from SR to cytosol, as well the Ca2+ entrance from extracellular medium to cytosol.
Representation of gastrointestinal areas of rat esophagus and stomach used to obtain tissue pieces. Figure also depicts tissue disposal for mounting esophagus as rings (1) or stomach fundus as strips (2) in the isolated organ bath system.
A: experimental traces of fundic strips during electrical field stimulation (EFS) at increasing frequencies (1–20 Hz). These responses were obtained in the absence (control) or in the presence of either tubocurarine (5 μM) or atropine (1 μM). B: means ± SE of EFS frequency-response curves in fundic strips: control (n = 36) and in the presence of tubocurarine (5 μM; n = 6) or atropine (1 μM; n = 6). Inverted bars indicate reduced tonus in the presence of atropine. *P < 0.05, ANOVA, post hoc test Holm-Sidak.
A: experimental traces of isolated esophagus under electrical field stimulation (EFS) in a frequency of 10 Hz in the absence (control) or presence of tubocurarine (5 μM). B: means ± SE of contractions induced by EFS (1–20 Hz) in the absence (control, n = 36) or presence of tubocurarine (5 μM; n = 6) or atropine (1 μM; n = 6). *P < 0.05, ANOVA, post hoc test Holm-Sidak.
A: experimental traces obtained from strips of stomach fundus (left) or esophagus (right) under electrical field stimulation (EFS) at 10 and 20 Hz in the absence (control) or presence of caffeine (5 mM). B and C: means ± SE of contractile responses to EFS in fundus strips (B) or esophagus (C): control (n = 36) and previous addition of procaine (1 mM; n = 6) or caffeine (5 mM; n = 6). *P < 0.05, ANOVA, post hoc Holm-Sidak.
Evaluation of students’ knowledge regarding contractility of gastrointestinal tract
Student Answer, %
1. What kinds of muscle are present in the gastrointestinal tract?
Striated and smooth muscle
2. What is tetanic contraction?
3. What is the main neurotransmitter released from the parasympathetic system in the gastrointestinal tract?
4. Select the correct option regarding the location of the ryanodine receptor in the muscle cells.
The questionnaire was anonymously given to 47 undergraduate students of biology and health sciences. For P value, Wilcoxon signed ranks test was used, compared with the response obtained before the activity.
Cover: From material detailed in the following article: Bell FE, Wilson LB, Hoppmann RA. Using ultrasound to teach medical students cardiac physiology. Adv Physiol Educ 39: 392–396, 2015; doi:10.1152/advan.00123.2015.