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Structure of the Autonomic Nervous System (ANS)

by Thad Wilson, PhD
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    00:00 The Autonomic Nervous System.

    00:06 ANS mediates many of our classical homeostatic process such as temperature regulation, glucose specially in the blood, as well as blood levels of lipids.

    00:22 The plasma levels of oxygen, carbon dioxide and even pH.

    00:27 The heart and blood vessels are also innervated by the autonomic nervous system and will help us to control and regulate blood pressure.

    00:35 These doesn’t not only in the level of the heart, where you can control heart rate in contractility but also blood vessels where controls vascular resistance.

    00:46 The kidneys where also under ANS mediated homeostatic control things like pH, sodium levels and other electrolytes, osmolality even total body water.

    00:57 All of these items are being constantly regulated throughout the body and miniscule, and large changes are occurring because of the autonomic nervous system.

    01:11 So what are the structural divisions of the ANS? These are important, and also, it’s important to contrast this to the somatic motor system so do you have a good feel for what the differences are.

    01:25 In the somatic motor system, we go right from the spinal cord to the muscle of action.

    01:33 So this is one nerve that goes from the spinal cord to the muscle.

    01:38 In the ANS works different.

    01:42 The sympathetic nervous system synapses in sympathetic chain ganglia or autonomic ganglia.

    01:48 And that travels up and down in the spinal cord, innervating a multitude of various organs and of blood vessels all at the same time.

    01:57 So either somatic motor system really only innervates a muscle in more specifically a few fibers in that muscle.

    02:05 The ANS can innervate large slots of organs in our organ systems.

    02:09 The parasympathetic nervous system, usually has a synapse both in the spinal cord as well as in an autonomic ganglia that’s located in close proximity to the organ or other item that its going to be innervating.

    02:25 So that’s a big difference between the sympathetic and parasympathetic.

    02:29 And that is where the autonomic ganglia are located.

    02:33 Autonomic ganglia are located in a close proximity for the sympathetic nervous system.

    02:38 And then, for the parasympathetic nervous system they are located close to the organ of action.

    02:44 That big difference is important because it means that the presynaptic versus postsynaptic nerves are gonna be different lengths for the different divisions of the autonomic nervous system.

    02:57 Sympathetic has a short pre, long post.

    03:00 While the para sympathetic has a long pre, short post.

    03:05 So once you have the nervous system output to the receptor, what different neurotransmitters are being released? And what receptors are gonna be engaged? If we go back to our example, in where we gonna compare things to the somatic motor system, lets look at that first.

    03:23 So normally, here again, we have the soma or cell body in the spinal cord.

    03:27 The nerve will go the length until it innervates a few muscle fibers it releases acetylcholine.

    03:35 It is a cholinergic nerve.

    03:38 That acetylcholine leaves the acts on terminal, goes across the synaptic cleft in this case the neuromuscular junction, and binds to a nicotinic type 1 acetylcholine receptor that is ionotropic.

    03:52 Meaning, that allows ions to travel once the acetylcholine binds to it.

    03:57 This is a very classic way of signaling.

    04:01 Now the automatic nervous system utilizes a little bit more complex of a process.

    04:06 So let’s compare and contrast.

    04:09 If we take the sympathetic nervous system first, you have your first spinal nerve soma and then it will synapse in an autonomic ganglia.

    04:20 This autonomic synapse also use acetylcholine.

    04:23 So this is a presynaptic nerve.

    04:26 It releases that acetylcholine goes cross the synaptic cleft and bind to a nicotinic type 2 receptor.

    04:35 These particular receptors also allow for ions to travel through and will stimulate another nerve to be released.

    04:45 That other nerve to be released can be one of two types.

    04:48 Either another cholinergic nerve or a noradrenergic nerve.

    04:53 So lets go through the cholinergic nerves first.

    04:57 Usually in these case, that cholinergic nerve will synapse and release its acetylcholine go across the synaptic cleft and bind to muscarinic type 3 receptors.

    05:09 Now these muscarinic receptors are G-protein coupled receptors (GPCRs) rather than, letting the ions through, you’re gonna stimulate or cause a transduction of their signal via G-protein and then stimulate something else, such as, allowing for calcium influx, changing the amount of phospholipase C, so forth.

    05:32 Norepinephrine or noradrenergic nerve can also be part of this sympathetic nervous system response.

    05:39 This organ, postganglionic nerves that released norepinephrine into a synaptic cleft.

    05:47 They have a plethora of receptors to bind too.

    05:51 They can bind to alphas or betas.

    05:54 And there is a number of different types of each of this receptors.

    05:57 There is alpha 1, there’s alpha 2, there’s alpha-2C.

    06:01 There’s beta 1, beta 2s, beat 3s, and they will be a different low-cals in the body depending upon the density of which they are.

    06:10 Then they will get a metabolic response, vascular response or whatever change that particular organ will undertake.

    06:18 So that’s the noradrenergic pathway through adrenergic receptors, whether they’re alpha or beta.

    06:25 But remember, there are few examples of cholinergic sympathetic nerves.

    06:32 Finally, we use our last comparing contrast by looking at the parasympathetic nervous system.

    06:37 Here the preganglionic nerve, the nerve is longer in nature, but its still uses acetylcholine.

    06:44 He releases acetylcholine and that goes across the synaptic cleft and binds to a nicotinic type 2 receptor.

    06:53 From here, that stimulates another nerve and that second nerve is also cholinergic.

    07:00 So then, this postganglionic nerve is cholinergic releasing acetylcholine into the synaptic cleft.

    07:06 This can bind to a number of different types of muscarinic receptors M1s, M2s, M3s.

    07:14 You know, in there are it seems to keep increasing the amount of the M's they want to denote.

    07:20 But these was engaged things like smooth muscle, glands various types of processes in which you would want to change from the parasympathetic nervous system.

    07:31 This are G-protein coupled receptors as well.

    07:35 Therefore, when they get stimulated, they will stimulated G-protein, that will then do a particular action like activating enzymes or open a channel.

    07:44 If we compare and contrast all of these, we’ll notice some similarities.

    07:50 In first similarity, acetylcholine is also always the first nerve in this system.

    07:57 The first synapse is always nicotinic.

    08:01 In the somatic, its nicotinic type 1.

    08:04 In the sympathetic comparison sympathetic, its nicotinic type 2.

    08:08 This is then where a things start to change after the first synapse, cause now whether you could have a cholinergic or adrenergic nerve, and then of course, the downstream receptors are quite a few of those.

    08:20 Another difference with nerves are the ANS axon terminals are a little bit different.

    08:27 Instead of being a single axon terminal, we are kind of bugs out and has a nice synapse with one particular low-cal.

    08:36 Axon terminals in the ANS are often times in bead like strings.

    08:41 These allows for more wide spread engagement of the peripheral tissue rather than just a single response.

    08:49 These particular axon terminals, also turns varicosities, will allow for more neurotransmitter to be released across that range of tissue.


    About the Lecture

    The lecture Structure of the Autonomic Nervous System (ANS) by Thad Wilson, PhD is from the course Neurophysiology.


    Included Quiz Questions

    1. Close to the end organ
    2. Far from the end organ
    3. Close to the spinal cord
    4. Within the dorsal root of the spinal cord
    1. Nicotinic type 2
    2. Nicotinic type 1
    3. Muscarinic type 1
    4. Muscarinic type 2
    1. Nicotinic type 2 receptors
    2. Muscarinic type 1 receptors
    3. Muscarinic type 2 receptors
    4. Nicotinic type 1 receptors
    5. Muscarinic type 3 receptors
    1. Has long presynaptic nerves
    2. Has short presynaptic nerves
    3. Has long postsynaptic nerves
    4. Length is not important for determining the action

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

     Thad Wilson, PhD

    Thad Wilson, PhD


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