Effectors of the Autonomic Nervous System (ANS)

by Thad Wilson, PhD

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    00:00 Autonomic Nervous System Effectors.

    00:05 Now, we get to talk a lot about all this different things that happen throughout the body that will able to be doing something.

    00:14 We are not just gonna look at things. We are gonna look it action today.

    00:20 The Autonomic Nervous System is a large cohort that’s controlling a number of aspects of the body.

    00:28 What we have here are two different columns.

    00:31 These are spinal cord columns.

    00:34 The first one is the autonomic nervous systems, sympathetic component.

    00:39 And then, on the other side, we have the parasympathetic component.

    00:44 The sympathetic component you know because it has paravertebral chain ganglia on both sides of the spinal cord.

    00:53 This will act as relay spots and sometimes where the soma or cell body of the nerve will be.

    01:01 The parasympathetic nervous system, remember, primarily comes from cranial nerve number 10.

    01:09 So this vagus nerve will innervate many of the different organs in the body.

    01:13 These are the same organs that would innervated by those particular sympathetic fibers that come off of the spinal cord.

    01:21 In the parasympathetic nervous system then you also have the splanchnic nerve and some that come from the sacral area. And they will innervate things like the bottom portion of the GI track, places like the bladder and the reproductive organs.

    01:38 So we go through this process, I think it’s best to do this one organ at a time.

    01:45 And so, we do one organ, the next organ, and keep going through those.

    01:48 We’ll talk about what’s function that’s involve, as well as what receptors will mediate that particular function.

    01:57 Let’s start off with the heart.

    02:00 The heart is going to be innovated by both the sympathetic and parasympathetic nervous system.

    02:07 The SA node, and this is again the area that’s going to control heart rate.

    02:13 If it’s engage by the sympathetic nervous system it’s through Beta-1 (β1) adrenergic receptors, and this will increase heart rate.

    02:23 In contrast, the parasympathetic nervous system, is mediated through muscarinic receptors and that decreases heart rate.

    02:35 The conduction system of the heart especially around the AV node, velocity can change in response to sympathetic comparison sympathetic stimulation.

    02:47 Beta-adrenergic receptors here also increase conduction velocity in the sympathetic nervous system.

    02:54 While muscarinic receptors, this decrease the conduction velocity.

    03:00 In terms of contractility, which is the contraction, the strength of the heart, this is gonna be mediated also by beta-adrenergic receptors.

    03:11 But now, this increases contractility or an atrophy.

    03:16 Muscarinic reflects don’t really have anything to do with the ventricles, to push blood around to the body or to the lungs.

    03:25 What happens to the blood flow that goes to the skin in the muscle? Here we need to talk through which things cause constrictions and dilations.

    03:37 So in the skin, we mainly have alpha-adrenergic receptors that cause vasoconstriction.

    03:44 So vasoconstriction is going to be decreasing the luminal diameter of a blood vessel that reduces the amount of blood flow.

    03:54 Beta-2 (β2) adrenergic receptors are located in skeletal muscle and they can cause a vasodilation.

    04:01 That said, they are usually not engaged in normal physiology.

    04:07 You have to give us supra physiological dose of a drug to get this receptors to be in acted.

    04:13 So normally, our response is having a vasoconstriction in response the blood vessels of skeletal muscle.

    04:21 So you vasoconstrict them in terms of the sympathetic nervous systems response.

    04:26 Hopefully, you’ve looked now on the parasympathetic side and notice there is no intervention of blood vessels to the skin or to the muscle from the parasympathetic nervous system.

    04:41 That’s said, there are some relaxing factors that can be released. And some of this have been associated with some parasympathetic innervation especially in the facial region.

    04:52 The Autonomic Nervous System and the Lung.

    04:55 So what changes happen with the lung in regards to a sympathetic and parasympathetic nervous system? The main component with the lung are the bronchioles.

    05:06 If you dilated a bronchiole, what will get is an increase in a diameter. And if you have an increase in diameter, you'll have a reduction and a resistance and therefore more flow.

    05:19 And this sympathetic nervous system does just that by dilating bronchioles.

    05:25 It does that through beta-adrenergic receptors. The opposite response is a constriction.

    05:32 And this is mediated by this parasympathetic nervous system through muscarinic receptors.

    05:41 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.

    06:01 The enteric nervous system gives information from the sympathetic and the parasympathetic.

    06:06 But it also operates on its own. So I have to throw that caveat in as we go through this particular table.

    06:15 So what are the effects on smooth muscle walls? The sympathetic nervous system relaxes them.

    06:23 The parasympathetic nervous system contracts them.

    06:26 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 to the GI tract.

    06:42 If you have a contraction, it will speed it up. So as you speed up food that travels through the GI Tract.

    06:51 So this effects gastric motility.

    06:55 If you want to think about this in terms of these sphincters. Now, this are the areas of a gastrointestinal tract that act as gates.

    07:03 You will get a sympathetic nervous system will cause of vasoconstriction, or sorry, a constriction and with this dose is prevent the food stuff form going through that particular gate.

    07:15 The parasympathetic nervous system relaxes those gates. So that food will move through the GI system.

    07:23 In terms of secretions, it’s kind of interesting, but both the sympathetic and parasympathetic nervous system increase salivary secretions.

    07:33 They do it via little different mechanisms though.

    07:36 The beta-adrenergic increase from the sympathetic nervous system, creates a more mucusy saliva.

    07:46 And the parasympathetic nervous system secretes more of a watery saliva.

    07:51 And so this are differences that can happen in salivary secretion but both tend it increase it.

    07:58 It’s just, what type, watery or serous solutions or more mucusy solutions.

    08:04 In terms of stomach secretions, the parasympathetic nervous systems increases gastric secretions.

    08:11 Also pancreatic secretions is the parasympathetic nervous system.

    08:15 Again mediated by muscarinic receptors.

    08:18 the sympathetic nervous system doesn’t have anything to do with the secretion end only with the motility and for the GI Tract.

    08:28 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? The bladder. What we’re gonna do here is cause either a relaxation or a contraction.

    08:51 Remember, if you are relaxing the bladder, you are not then wanting to have that urge to void.

    08:58 If you are contracting it, this is the time where you may wanted then, if it’s socially appropriate to void your bladder.

    09:06 These sphincters are also involve in that same kind of a maneuver.

    09:11 There will be a constriction portion and a relaxation portion.

    09:15 Now again, this is the autonomic sphincter. There is also a voluntary or skeletal muscle component that you control from your cortex.

    09:24 So this is just the one part of being able to void the bladder but not the voluntary component.

    09:35 What about the reproductive organs? The autonomic nervous system both the sympathetic and para sympathetic nervous system innervate the reproductive organs for both males and females.

    09:49 If you think about for the male genitalia, the sympathetic nervous system has to do with ejaculation.

    09:56 The parasympathetic nervous system has to do with the erection or increasing blood flow.

    10:02 In terms of the female genitalia, it’s very similar.

    10:06 You during contractions are sympathetically mediated event. While increasing this secretions and increasing the amount of blood flow is a parasympathetic nervous system.

    10:18 These is one of the organ systems that I think or should be most highlighted because there is a duo activation and needs to happen.

    10:28 So in this case, you need to have both in increase of blood flow and ejaculation to happen.

    10:34 So they are working together in concert. Rather than, working in an opposition to each other.

    10:40 So a lot of the different of the organ systems we saw that one constricted and one dilated.

    10:45 and so they seemed to be opposites.

    10:47 But in the reproductive organs, they can work in concert to do a function.

    10:53 The eyes, also innervated by the sympathetic and parasympathetic nervous systems.

    10:58 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.

    11:09 The Eye. Sympathetic and parasympathetic innervation both affect the eye.

    11:15 The sympathetic nervous system affects radial muscles and this will dilate the pupil, so you get more light in.

    11:21 And as you do this, this increases via alpha-adrenergic receptors.

    11:27 The opposite is a pupil constriction.

    11:30 This constriction is mediate by muscarinic receptors from the parasympathetic nervous system.

    11:36 Finally, as you think about ciliary muscles, They’ve can be dilation or occurrence from the sympathetic nervous system and constriction for the parasympathetic nervous system.

    11:48 So you can see here that dilation seems to be more sympathetically mediated.

    11:54 And the constrictions and contractions more parasympathetically nervous mediated.

    12:03 Now, let’s address some of the skin specific components.

    12:08 We already talked about blood vessels in the previous one. But now, we are gonna go through and talk about the skin appendages.

    12:15 And you might ask, appendages I don’t have anything growing off my skin.

    12:20 Maybe you do.

    12:23 Sweat glands are called skin appendages because they are part of the glandulous structure.

    12:30 But they will end up being a structure of their own.

    12:35 They are mediated by the sympathetic nervous system and muscarinic receptors.

    12:41 Wait, wait, wait, wait, wait.

    12:43 I said muscarinic receptors.

    12:45 Did you mean it? Yes I did.

    12:47 This is a rare time when the sympathetic nervous system is using a muscarinic receptor.

    12:54 Typically, these are for the parasympathetic nervous system, right.

    12:58 Correct.

    12:59 But in this case, this is an exception to the rule. We’re you use acetylcholine as a primary neurotransmitter and bind the muscarinic receptors. And it’s still under sympathetic control.

    13:15 The other type of skin appendage is hair.

    13:18 And so hair is sticking off the skin. You can modulate the hair though by contracting pilliary muscles.

    13:27 This Pilomotor muscles, allow for hair to standup. And this would be in a time that when you are very cold or if you are nervous, and your hair starts standing up, and this also can make little kind of pillary bumps or we leagues call goose bumps.

    13:46 This are mediated by alpha-adrenergic receptors and this is contraction of that smooth muscle.

    13:53 You notice that the parasympathetic nervous system here doesn’t activate skin appendages.

    14:01 Let’s now move on to tear glands.

    14:06 So lacrimal glands are innervated by the parasympathetic nervous system, and muscarinic receptors increase their secretions.

    14:16 The liver is important in being able to do a lot of different functions for the body.

    14:21 In this case, it is gonna be innervated by the sympathetic nervous system.

    14:26 It is going to be involve in gluconeogenesis, which is the production of the new glucose.

    14:33 It is also involve in glycogenolysis. And that is the breakdown of glycogen.

    14:39 Both of these two things will do increasing blood glucose.

    14:44 Either gluconeogenesis making new glucose or breaking down glycogen into glucose the liver then can release it, so the rest of the body can neutralize it.

    14:54 Adipose tissue is innervated by the autonomic nervous system. You will necessarily think of this, would you? Why would fat be innervate by the autonomic nervous system? But there are couple of times from a sympathetic event that it makes it important. Let’s go through those.

    15:10 Adipose tissue has beta-3 adrenergic receptors.

    15:16 These receptors, if engage, by epinephrine or norepinephrine cause lipolysis.

    15:22 Lipolysis is the breakdown of fat. Then what you would do is the adipose tissues will release free fatty acids into the blood.

    15:31 Another tissue as also adipose tissue is called a brown adipose tissue.

    15:37 Brown adipose tissue, especially in infant, is important for thermos regulation.

    15:42 They utilize these same beta-3 adrenergic receptors and end up causing heat production.

    15:48 So both white fat and brown fat are innervated by the sympathetic nervous system.

    15:54 The kidney is innervated by the sympathetic nervous system.

    15:57 and it does this to help regulate things like blood flow and glomerular filtration rate.

    16:04 The other thing that it does is stimulate the release of renin.

    16:08 And remember, when was such important molecule in starting the Renin Angiotensin Aldosterone System.

    16:15 The RAAS system allows you to reabsorb sodium and water. And this is an important process that is mediated by beta-1 adrenergic receptors.

    About the Lecture

    The lecture Effectors of the Autonomic Nervous System (ANS) by Thad Wilson, PhD is from the course Neurophysiology. It contains the following chapters:

    • Effectors of the ANS
    • ANS - Heart
    • ANS - Skin & Muscle Blood Vessels
    • ANS - Lung

    Included Quiz Questions

    1. Beta-1 adrenergic receptors
    2. Nicotinic receptors
    3. Muscarinic type 1 receptors
    4. Beta-2 adrenergic receptors
    5. Muscarinic type 2 receptors
    1. Vagus
    2. Facial
    3. Abducent
    4. Glossopharyngeal
    5. Occulomotor
    1. Alpha adrenergic
    2. Beta adrenergic type 1
    3. Nicotinic
    4. Muscarinic type 1
    5. Beta adrenergic type 2
    1. Beta adrenergic
    2. Nicotinic
    3. Muscarinic type 1
    4. Muscarinic type 2
    5. Alpha adrenergic

    Author of lecture Effectors of the Autonomic Nervous System (ANS)

     Thad Wilson, PhD

    Thad Wilson, PhD

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