Autonomic Nervous System: GI Tract

by Thad Wilson, PhD

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    00:01 What about the GI tract? How does the autonomic nervous system, both the sympathetic and parasympathetic mediate this? We have to throw one caveat in this before we go through the table and that is remember there is another division of the autonomic nervous system which is known as the enteric nervous system.

    00:22 The enteric nervous system gets information from the sympathetic and the parasympathetic but it also operates on its own, so I have to throw that caveat in as we go through this particular table.

    00:34 So what are the effects on smooth muscle walls? The sympathetic nervous system relaxes them the parasympathetic nervous system contracts them.

    00:47 So what does that mean practically? If you have a smooth muscle wall relaxation you’re going to slow down the food, slow down the food, as it travels through the GI tract.

    01:02 If you have a contraction, it will speed it up; so as you speed up food that travels through the GI tract so this affects gastric motility.

    01:14 If you want to think about this in terms of the sphincters, now these are the areas of the gastrointestinal tract that act as gates.

    01:24 You’ll get a sympathetic nervous system will cause a vasoconstriction, or sorry, a constriction, and what this does is prevent the foods stuff from going through that particular gate; the parasympathetic nervous system relaxes those gates so that food will move through the GI system.

    01:42 In terms of secretions, it’s kind of interesting but both the sympathetic and the parasympathetic nervous system increase salivary secretions.

    01:54 They do it by a little different mechanism though.

    01:57 The beta adrenergic increase from the sympathetic nervous system creates a more mucosy saliva and the parasympathetic nervous system secretes more of a watery saliva and so these are differences that can happen in salivary secretion but both tend to increase it, it’s just what type, watery or serous solutions or more mucosy solutions.

    02:25 In terms of stomach secretions, the parasympathetic nervous system increases gastric secretions.

    02:31 Also pancreatic secretions is a parasympathetic nervous system again mediated by muscarinic receptors.

    02:39 The sympathetic nervous system doesn’t have anything to do with the secretion end only with the motility and for the GI tract.

    02:48 What about the bladder? The autonomic nervous system also engages the bladder so that if you have urinary contents you need to know is it appropriate time or not to void that bladder.

    03:02 The bladder. What we’re gonna do here is cause either a relaxation or a contraction.

    03:11 Remember if you’re relaxing the bladder, you are not then wanting to have that urge to void, if you are contracting it, this is the time where you may want to then if it’s socially appropriate to void your bladder.

    03:27 The sphincters are also involved in that same kind of maneuver.

    03:32 There will be a constriction portion and a relaxation portion.

    03:36 Now, again, this is the autonomic sphincter, there is also a voluntary or skeletal muscle component that you control from your cortex, so this is just the - a one part of being able to avoid the bladder but not the voluntary component.

    03:54 What about the reproductive organs? The autonomic nervous system both the sympathetic and the parasympathetic nervous system enervate the reproductive organs for both males and females.

    04:09 If you think about, for the male genitalia, the sympathetic nervous system has to do with ejaculation.

    04:16 The parasympathetic nervous system has to do with erection or increasing blood flow.

    04:22 In terms of the female genetalia, it’s very similar.

    04:26 Uterine contractions are a sympathetically mediated event, while increasing the secretions and increasing the amount of blood flow is a parasympathetic nervous system.

    04:38 This is one of the organ systems that I think or should be most highlighted because there is a dual activation that needs to happen.

    04:48 So in this case, you need to have both an increase in blood flow and ejaculation to happen so they are working together in concert rather than working in opposition to each other, so a lot of the different organ systems we saw that one constricted and one dilated and so they seem to be opposites; but in the reproductive organs they can work in concert to do a function.

    05:14 The eye is also enervated by the sympathetic and the parasympathetic nervous systems.

    05:19 This is an important process in being able to get more light into the eye when you need to see more or protect it when you need to see less.

    05:29 The eye, sympathetic and parasympathetic enervation both affect the eye.

    05:35 The sympathetic nervous system affects radial muscles and this will dilate the pupils so you get more light in and as you do this, this increases via alpha adrenergic receptors.

    05:47 The opposite is a pupil constriction.

    05:50 This constriction is mediated by muscarinic receptors from the parasympathetic nervous system.

    05:56 Finally, as you think about ciliary muscles, they can be dilation that occurs from the sympathetic nervous system and constriction for the parasympathetic nervous system.

    06:09 So as you can see here the dilation seems to be more sympathetically mediated and the constriction and contraction is more parasympathetically nervous mediated.

    About the Lecture

    The lecture Autonomic Nervous System: GI Tract by Thad Wilson, PhD is from the course Neurophysiology.

    Author of lecture Autonomic Nervous System: GI Tract

     Thad Wilson, PhD

    Thad Wilson, PhD

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