Slow Waves – Gastrointestinal Motility

by Thad Wilson, PhD

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    00:01 What controls these GI movements? These come back to these interstitial cells of Cajal.

    00:08 These small little cells use a change in membrane potential to elicit different types of muscle contractions.

    00:17 The frequency, however, of these muscle contractions vary depending upon if you’re in the stomach, the small intestine or the large intestine.

    00:26 In the stomach, there are about 3 to 5 of these contraction waves that happen per minute.

    00:34 In the small intestine, it’s about 12 to 20.

    00:37 And the large intestine, about 6 to 8.

    00:42 Now, slow waves are very hard to kind of visualize, so I’m going to show you a few in the next couple of slides.

    00:48 The influence of these particular slow waves are usually not in terms of the rate, but rather their amplitude.

    00:56 The higher the amplitude, the greater the contraction.

    01:00 The lower the amplitude, the less of a contraction.

    01:04 And this is where smooth muscle differs from skeletal muscles.

    01:08 In skeletal muscle, either it contracts or it doesn’t.

    01:11 In smooth muscle, it’s gradated, meaning that it can contract harder or less hard with any particular muscle fiber.

    01:21 Okay.

    01:21 So how does this process work? Well, you have to develop tension and you have these waves occurring.

    01:31 So let’s look at this particular example of four slow waves.

    01:37 Each of the slow waves causes a little change in muscle tone.

    01:41 If there’s an increase in muscle tone, that’s a muscle contraction.

    01:46 What those spikes are at the top of membrane potential are action potentials.

    01:50 So it’s possible for a slow wave to reach and action potential.

    01:55 But it is not necessary.

    01:58 There still will be some contraction that occurs.

    02:01 This is in a stimulated condition such as if you were in a relaxed and digest condition of the parasympathetic nervous system.

    02:11 You see that in this case you have more action potentials occurring at the tops of these slow waves causing greater muscle contractions.

    02:22 This is an inhibited condition such as what might happen with the sympathetic nervous system.

    02:28 So it’s generating a little bit of a slow wave here.

    02:30 But it’s not enough to cause much of a change in muscle tone.

    02:35 So muscle tone is very much related to this slow wave, but also how many action potentials that are engaged once the slow wave reaches a certain amount of membrane potential.

    02:51 And so you might ask, “Well, what controls these slow waves?” Well, the upward slope of the slow wave is usually done by a calcium channel and the return of that slow wave back down to more of a resting membrane potential is done by a potassium channel.

    03:06 So it’s simply opening and closing the various channels done at different rates throughout the GI system.

    03:13 Remember, it’s slower in the stomach, faster in the small intestine and again slower in the large intestine.

    About the Lecture

    The lecture Slow Waves – Gastrointestinal Motility by Thad Wilson, PhD is from the course Gastrointestinal Physiology.

    Included Quiz Questions

    1. Small intestine
    2. Esophagus
    3. Stomach
    4. Large intestine
    1. 3-5
    2. 1-2
    3. 2-3
    4. 6-8
    5. 7-8
    1. 6-8
    2. 1-3
    3. 3-5
    4. 9-11
    5. 13-15

    Author of lecture Slow Waves – Gastrointestinal Motility

     Thad Wilson, PhD

    Thad Wilson, PhD

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