Conduction Illustrated Lecture Notes PDF

2.1 Unpacking Conduction 00:00:00 [MUSIC] 00:00:09 Hello and welcome to the first lecture in a series of lectures on nociceptive conduction. 00:00:15 This lecture is on unpacking conduction 00:00:18 [BLANK_AUDIO] 00:00:26 By the end of this lecture, I hope that you'll be able to define nociceptive c...

2.1 Unpacking Conduction 00:00:00 [MUSIC] 00:00:09 Hello and welcome to the first lecture in a series of lectures on nociceptive conduction. 00:00:15 This lecture is on unpacking conduction 00:00:18 [BLANK_AUDIO] 00:00:26 By the end of this lecture, I hope that you'll be able to define nociceptive conduction, recognize the pathway for action potentials in the conduction phase of nociception. 00:00:36 Describe how the structure of a neuron predicates its function and identify the function of the following structures, dorsal root ganglion, track of Lissauer and dorsal horn. 00:00:46 [BLANK_AUDIO] 00:00:51 As a brief reminder, here are the five steps of nociception. 00:00:54 This particular lecture is on conduction. 00:00:57 [BLANK_AUDIO] 00:01:03 Conduction is the process by which an action potential travels from a peripheral sensory receptor along a sensory neuron, also known as that first order neuron, to the dorsal horn of the spinal cord where it's synapses on a presynaptic terminal. 00:01:20 As mentioned in other lectures, this particular phase of nociception is often combined with transmission which we will discuss in another series of lectures in this course. 00:01:30 [BLANK_AUDIO] 00:01:35 Okay, this slide think of it as an overall roadmap for conduction. 00:01:41 First for the body below the head, the sensory neurons which include nociceptors carry sensory information via the dorsal root ganglion and the track of Lissauer to the dorsal horn of the spinal cord. 00:01:57 For the head and the face, the sensory neurons carry sensory information via the trigeminal ganglion and the spinal trigeminal nucleus found in the medulla. 00:02:08 So using this slide, 00:02:10 [BLANK_AUDIO] 00:02:13 In our information of stimulus, come down and interact with a receptor, the sensory receptor and again it can be a non-nociceptive receptor or a nociceptor. 00:02:25 Once that receptor has been activated, an action potential will be generated and be sent along this first order neuron which is the sensory neuron, okay? 00:02:34 To the spinal cord and in particular, it's going to interact with presynaptic terminals in the dorsal horn. 00:02:41 But before it actually reaches the dorsal horn, it travels via the track of Lissauer and we will discuss that a little later 00:02:48 [BLANK_AUDIO] 00:02:52 Okay, sensory neurons. 00:02:55 Different types of sensory neurons predicate the type of encoded stimuli being delivered to the dorsal root ganglion. 00:03:02 Sensory neurons are classified by their size, speed, and the thickness of their myelination. 00:03:11 As has already been discussed, sensory neurons that are believed to carry noxious stimulus primarily include the A-delta and C fibers. 00:03:21 Larger nerves, sensory neurons are believed to transmit low threshold mechanical and proprioceptive information while smaller sensory neurons are thought to transmit nociceptive and thermal information. 00:03:36 Now in recognition that sensory neurons including A-delta and C fibers carry this noxious information, they would are generally considered to be smaller sensory neurons. 00:03:49 So as mentioned in a previous lecture, it's really inconclusive whether A-beta can also carry noxious stimulus as it hasn't necessarily been thoroughly supported in the literature. 00:04:00 And we think about the application of this information, the speed of the signal from the receptor is determined by the type of the primary afferent nerve. 00:04:09 Given a nociceptive stimulus is carried by A-delta and C fibers, relatively speaking, A-delta is going to be faster and offer faster impulses or action potentials to the brain than your C fibers would. 00:04:25 Consequently in the literature, A-delta pain is considered to be fast pain while C fiber noxious stimulus is considered to be slow pain. 00:04:33 [BLANK_AUDIO] 00:04:37 The dorsal root ganglion, the dorsal root ganglion are a group of cells that are pseudo-unipolar neurons that conduct information from the periphery into the spinal cord. 00:04:49 For clarification purposes, a pseudo-unipolar neuron is a type of neuron that has one extension from its cell body. 00:04:56 So it's going to look something like this. 00:04:58 You have your cell and it's going to be an extension basically between a receptor which we're going to put right here, and your spinal cord. 00:05:07 So this would be a pseudo-unipolar neuron. 00:05:10 In this case again, it extends from the peripheral nervous system, so here, to the central nervous system. 00:05:18 Another way to view the DRG is that it is a group of cells that conduct sensory information from receptors such as thermal receptors, thermonociceptors, proprioreceptors, chemoreceptors etc., to the central nervous system. 00:05:33 For discriminatory and nociceptive information from the body below the head, the dorsal root ganglion carries these signals to the presynaptic terminal within the dorsal. 00:05:42 Or posterior horn of the spinal cord where the terminal interfaces with interneurons and second order neurons found in the dorsal horn. 00:05:49 Now this ends with this course identifies as the conduction phase of nociception. 00:05:56 As stated earlier, nociception from the face in the head do not use all the same pathways as the rest of the body does below the head 00:06:04 [BLANK_AUDIO] 00:06:07 Okay, the track of Lissauer is a pathway for first order neurons carrying light touch, pain and temperature information from the peripheral sensory receptors to the dorsal column of the spinal cord. 00:06:22 The unique characteristic the track of Lissauer is that from any level, it ascends and descends up to four segmental levels. 00:06:30 Anatomically, it is found dorsal to the dorsal horn grey matter. 00:06:35 Clinically this means that information originating at the level of L1 dorsal root could polarize terminal synapses at the dorsal horn from T9 and L5. 00:06:46 This is thought to be redundant system that provides a series of neurological pathways for sensory information to reach the brain. 00:06:54 Please see that lecture Lissauer's track illustrated for a visual representation of how the track of Lissauer works. 00:07:00 [BLANK_AUDIO] 00:07:04 Okay, so the dorsal horn, [COUGH] the dorsal horn of the spinal cord, it is the first site for integration and processing of incoming sensor information. 00:07:15 Now given its role and function, the dorsal horn is found at all levels of the spinal cord which has significant clinical relevance, and we discussed pain and perceived pain patterns. 00:07:26 From the dorsal horn ascending, so going up to the brain, neural projections travel the spinal column to the midbrain carrying modulated sensory information from the dorsal horn. 00:07:37 While extremely relevant to conduction, this is actually a process of transmission in which the literature recognizes transmission. 00:07:44 For our course, this is a separate process which is the third step in nociception. 00:07:50 [BLANK_AUDIO] 00:07:54 Okay, so the takeaway from the lecture, nociceptive conduction is the second step in this course in the five steps of nociception. 00:08:05 During conduction, an action potential travels from the nociceptor along a first-order afferent neuron to the pre-synaptic terminal in the dorsal horn. 00:08:14 The structure of a neuron predicates its function. 00:08:18 Each of the following anatomical structure plays an important role in nociceptive conduction, the dorsal root ganglion, the track of Lissauer, and the dorsal horn. 00:08:28 Some other points, primary sensory afferent neurons carry information as a quick review from our receptors to the dorsal root ganglion, or the trigeminal ganglion for the head and face. 00:08:39 From the DRGs, they go to the presynaptic terminals via Lissauer's tracks. 00:08:45 And from the presynaptic terminal interfaces within the posterior gray column or the dorsal horn or the spinal trigeminal nucleus in the thalamus, it is then carried to the brain. 00:08:57 Nociception can be very fast or slow predicated by again the type of the nerve, so A-delta being fast while your C fiber is being slow. 00:09:06 Primary nociceptors are not necessarily slow conducting or small diameter fibers which is represented by again your A-delta fibers. 00:09:14 For additional information in an illustration of nociceptive conduction, please see the lecture titled nociception conduction illustrated. 00:09:24 [BLANK_AUDIO] 00:09:27 This concludes our lecture on unpacking conduction. 00:09:31 If you have any questions, please reach out to me or Dr. Stern. 00:09:35 Thank you and speak at you next time. 00:09:37 [BLANK_AUDIO] cielo24 | what’s in your video? | cielo24.com 2.2. Sensory Neuron Types 00:00:00 Hello, and welcome to another lecture on integrated pain science. 00:00:05 This lecture is on sensory neuron types. 00:00:08 [BLANK_AUDIO] 00:00:10 Our pain declaration for this course, 00:00:12 [BLANK_AUDIO] 00:00:16 And our objectives or scaffold for this lecture. 00:00:20 The overall purpose of this lecture is to have each of you be comfortable or familiar with the many different types of classification or categorization schemes that are used for sensory neuron types. 00:00:34 With this in mind, by the end of this lecture, I hope that you'll be able to define a sensory neuron. 00:00:40 That you'll be able to differentiate neurons by either their grouptype, fiber-type, name, or order, as well as recognize the four primary afferent nerve types. 00:00:50 [BLANK_AUDIO] 00:00:54 So what is a sensory neuron? 00:00:57 A sensory neuron is a type of primary afferent neuron or nerve, which is also a type of pseudo unipolar neuron that transmits sensory information from receptors to the dorsal root ganglion. 00:01:12 Pseudo unipolar neurons are nerves without dendrites. 00:01:17 Developmentally, these neurons began as bipolar neurons. 00:01:20 And let me go ahead and show you what a bipolar neuron looks like. 00:01:25 It looks like this. 00:01:29 So we have our extensions from the cell body going either way, loops with extensions again going like this, okay? 00:01:38 Now, developmentally, over time, these then become pseudo unipolar neurons, which have a single structure that extends from the cell body to a peripheral receptor back to the dorsal horn of the spinal cord. 00:01:53 So that looks like here, and you will see this again and again within this course. 00:01:57 We have our receptor, which extends via an axon to the dorsal root ganglion, and then into the dorsal horn of our spinal cord. 00:02:09 And I'm just going to draw this really quickly, okay? 00:02:13 These nerves come into the dorsal horn, and we have our cell body here. 00:02:19 So this is what a pseudo unipolar neuron looks like. 00:02:23 [BLANK_AUDIO] 00:02:28 Okay, now, with regards to the classification schemes for sensory neuron types, there are two primary schemes within the literature. 00:02:36 And they are a group classification system and fiber-type classification system. 00:02:42 With regards to the group classification system, they're rated from I to IV, and some literature, V. 00:02:48 And they use they Roman numeral with I being the fastest and IV or V being the thinnest. 00:02:58 And again, that is also attributed to how well myelinated they are. 00:03:03 The type-I are going to be the thickest as far as myelination with type-IV or V being the thinnest. 00:03:13 For fiber-type classification systems, they're really determined by the relative speed of the neuron. 00:03:20 And of course, that is attributed to certain structural characteristics such as myelination. 00:03:25 And so with regards to the rating system from A to C with A being the fastest, these are going to be your fiber types that have the highest level myelination. 00:03:37 B are going to be your moderate speed neurons with moderate myelination, and your C-type fibers are going to be slow with low myelination. 00:03:46 Notably, for us within the context of nociception, this is the most common primary afferent neuron. 00:03:53 Now, within this fiber-type classification system, there is also an inner class rating, which also speaks to the speed within A, B, and C categories. 00:04:03 And they are rated from alpha, which is fastest, delta being the slowest. 00:04:07 [BLANK_AUDIO] 00:04:12 Okay, so there are other types of categorization schemes within sensory neurons. 00:04:19 And in some cases, you might see a neuron being classified either by their magnitude or mode. 00:04:26 So outside of our standard classification schemes such as seen on this page, neurons can be based on what we know to adequately activate them, or in other words, what best activates them. 00:04:39 On one hand, we have the magnitude of the stimulus. 00:04:43 And this is going to be the magnitude of stimulus that is needed to activate them with noxious being high and non-noxious being low in a non-sensitized system. 00:04:55 And then on the other hand, we have the mode of stimulus or the type of stimulus, which can either be mechanical, temperature, or chemical stimuli that activates that neuron. 00:05:05 Now, there are other ways to classify nociceptor and the respective sensory neurons other than magnitude and mode. 00:05:14 However, this will not be covered in this course primarily for the reason that it's associated with the neuro, anatomical, and molecular characteristics that are associated with the neurons. 00:05:27 And as such, we don't delve deeply enough into cellular physiology to really appreciate this classification system. 00:05:35 [BLANK_AUDIO] 00:05:39 And okay, so we're not done. 00:05:42 [LAUGH] There are other classifications of sensory neurons and These ordered neurons are a representation of an anatomical order or a hierarchical organization of neurons in the sensory nervous system. 00:06:02 They are going to be your first, second, third, and fourth-ordered neurons. 00:06:07 And actually, I'm going to use a pointer to kind of go through this as we discuss it. 00:06:13 The first-order neuron is the primary afferent neuron that extends from the sensory receptor to the dorsal horn. 00:06:22 In some cases, this is also considered to be the sensory cell. 00:06:27 These first-order neurons then synapse with second-order neurons again at the dorsal horn of the spinal cord. 00:06:35 And the second-order neurons then in turn synapse on third-order neurons. 00:06:42 Now, third-order neurons are generally found in ours, and with regards to the nociception within the thalamus. 00:06:48 And they then relay information to other sensory areas of the cerebral cortex. 00:06:54 Third-order neurons then in turn synapse on fourth-order neurons. 00:06:57 And fourth motor neurons are typically found in the associated sensory areas of the cerebral cortex. 00:07:03 [BLANK_AUDIO] 00:07:08 Okay, so what are the four main primary afferent sensory neuron types? 00:07:15 They are the A-alpha, A-beta, A-delta, and C-fibers. 00:07:24 As you can recall, the A-alpha are going to be your fastest classification of nerve. 00:07:30 And these nerves typically carry non-noxious information from mechanical receptors. 00:07:37 And this is going to be stimulus that carries information from our joints and muscle tissues. 00:07:45 And is then therefore, interpreted to our brain has proprioception, that's just one example. 00:07:51 A-beta relatively faster than your other types of nerves such as Adelta and C also carry non-noxious information from receptors that are mechanical sensitive or mechanically sensitive. 00:08:05 And these nerves typically carry information on touch and pressure, that is, information that will eventually be experienced as touch and pressure. 00:08:14 Now, there is some thought that these fibers do have three nerve endings, that is, they may, in fact, carry noxious stimulus information, but the information in the literature is limited. 00:08:26 And so at this point, all I want you to remember is that A-beta carries non-noxious information with regards to touch and pressure. 00:08:36 Then we have A-delta which, again, are relatively fastest compared to C, and these will carry both noxious and non-noxious information. 00:08:48 A-delta will carry noxious mechanical and thermal information, as well as non-noxious thermal information. 00:08:59 C-fibers which are slowest fibers carry both non-noxious and noxious information from each one of the modes of stimuli, that being thermal, chemical, and mechanical. 00:09:11 [BLANK_AUDIO] 00:09:13 Okay, so in the presence of injury, these afferent neurons may also project polymodal information. 00:09:22 To this point, many A-delta neurons are chemically sensitive and respond to injury and/or a chemical stimulus such as capsaicin. 00:09:33 And this leads to a lower threshold for thermal noxious stimulus, such as we would see, or which would occur in peripheral sensitization. 00:09:43 Under circumstances of central sensitization, we may actually see a lower threshold for mechanical stimulation. 00:09:49 Within the literature, mechanically sensitive sensory neurons are often polymodal thermal nociceptors as well. 00:10:00 One important distinction is how we conceptually understand fast versus slow pain. 00:10:05 Current theory proposes that our initial experience with pain, what some would for call our first pain is mediated by faster nerves, while slower or secondary pain is mediated by slower nerve fibers. 00:10:19 So for example, if you were to cut yourself, the initial noxious information could be carried by the A-delta nerve fibers. 00:10:29 We would then experience the associated sharp sensation of the cut first. 00:10:33 Then noxious information being carried by slower nerves to C-type fibers would create an experience of an after soreness or burn that we would call the second pain. 00:10:44 [BLANK_AUDIO] 00:10:48 Okay, so our takeaways for sensory neuron types. 00:10:51 First, a sensory neuron is a primary afferent neuron that transmits sensory information from receptors, that is, peripheral receptors to the dorsal root ganglion. 00:11:03 Two, neurons in nociception are classified by ground types, group types, I apologize, group types, fiber types, name, and by the order of the neuron within the literature. 00:11:15 And then there are four primary neuron types, they are A-alpha, Abeta, A-delta, and C-type fibers. 00:11:24 This concludes our lecture on neuron types. 00:11:28 If you have any questions, please reach out to me or Dr. Stern. 00:11:31 Thank you, and speak at you next time. 00:11:33 [BLANK_AUDIO] cielo24 | what’s in your video? | cielo24.com 2.3 Tract of Lissauer Illustrated 00:00:01 Hello and welcome to this lecture which is Lissauer's Tract Illustrated. 00:00:06 As it sounds this lecture is going to be slightly different. 00:00:11 I will be presenting this as a traditional lecture but embedded in this lecture is a video of me illustrating the clinical application and more or less the anatomy of the Lissauer's tract. 00:00:23 [BLANK_AUDIO] 00:00:32 So by the end of this lecture I'm hoping that you will be able to draw the path of an action potential during nociceptive conduction up to the Lissauer's Tract. 00:00:40 I hope that you will also be able to visually appreciate the role of Lissauer's tract in relation to nociceptive conduction 00:00:45 [BLANK_AUDIO] 00:00:50 Before we dive into this video, the tracker was ours a pathway for first order neurons carrying light touch, pain and temperature information from the peripheral sensory receptors to the dorsal column of the spinal cord. 00:01:04 The unique characteristic of the tract Lissauer is that from any level, it can ascend up to three segmental levels or descent. 00:01:11 Now, I will say that some of the literature varies as far as how far these levels or these afferent nerves will travel. 00:01:21 It can be anywhere from two to four, but the majority of the literature that I have read states three. 00:01:29 Anatomically is found in dorsal kind of dorsal laterally to the dorsal horn gray matter. 00:01:36 Clinically this means that information originating at the level of the L1 dorsal root could depolarize terminal synapses at the dorsal root horn from T9 and L5 if it did travel a senator descent four segments. 00:01:50 This is thought to be redundant system that provides a series of neurological pathways for sensory information to reach the brain. 00:01:58 If you consider a spinal cord injury that involves all three while the side injury does matter to simplify this, let's say that the entire level has a Lissauer. 00:02:08 While afferent first order neurons level L3 dorsal root may not be able to synapse on second order neurons at the same level. 00:02:16 Information on pain, crude touch, and temperature, bypasses injury and synapse on the dorsal horn above the site of the Lissauer. 00:02:24 Notably, those neurons at synapse at lower levels, for example L3, L4, may be impacted by a Lissauer in L2. 00:02:32 [BLANK_AUDIO] 00:02:35 So let's go ahead and start the video. 00:02:38 [BLANK_AUDIO] 00:02:40 All right, let's get started. 00:02:42 I think the first step I like to do is a cross section of the spinal cord. 00:02:48 Just to give you an idea, actually I don't want to use orange. 00:02:53 Let's use purple, blue not, this is purple. 00:02:56 I have borrowed my kids crayola set, so hopefully they don't mind too much. 00:03:02 Okay, so when we are thinking about location of the Lissauer's Tract, I wanted to give us an overall indication of where that would be within a cross section of the spine. 00:03:13 So cross section of the spine, we're going to have our dorsal and our ventral horns. 00:03:19 And the Lissauer's Tract in relation to the dorsal horns can be located just around here. 00:03:28 So that posterior lateral aspect of the dorsal horn. 00:03:33 Now in keeping with the same colors, let's try to show a representation of what happens to action potentials that come from our peripheral nervous system from our receptors into the spinal cord via Lissauer's tract. 00:03:52 And I'm going to draw, very quickly here more or less a very simple illustration of different segments of the spinal cord. 00:04:06 And within this we're going to go ahead and do mark this orange area as the Lissauer's tract specifically on this side of the spinal column. 00:04:15 And then just to the side of that we're going to have a little circle here to signify some of the cells of the dorsal horn where sensory information come and turn on our second order sensory neurons. 00:04:31 So, in recalling how action potentials are generated from sensory receptors, we're going to have impulses created by activation of receptors. 00:04:45 So let's say we have a receptor here, okay? 00:04:48 We have little impulses or a little stimuli that come in and activate this receptor. 00:04:55 This receptors will cause an action potential that will travel along this first order neuron, okay? 00:05:03 Now, just recall that this first order neuron is in fact a pseudo unipolar neuron. 00:05:09 This, first order neuron will travel from the periphery to the central system and will then in this case, go ahead and join presynaptic terminals here just before they activate second order neurons. 00:05:28 Now what can happen at this point is that impulses or action potentials can be sent up ipsilateral from the stimulus. 00:05:34 So it'll come up this way or it can cross over the white commissure and travel contralateral upwards towards the brain. 00:05:42 And just for our purposes, let's go ahead and just say this is the center part of the brain or the spinal cord. 00:05:49 Okay now where Lissauer's tract comes into play? 00:05:54 Stimulation of receptors in the same area sometimes can travel not just to the same level of the spinal cord but can ascend or descend upwards of one to three segments above that site of stimulation. 00:06:09 So let's say in this particular instance, we have a receptor here and we're going to use green. 00:06:13 It's an [INAUDIBLE] Over and very similar to this red first order neuron. 00:06:19 It's going to move towards the dorsal horn. 00:06:22 However, instead of synapse and directly on the same level, it's going to ascend to whereby it will then synapse or interact with second order neurons, two segments above the original segment of action potential generation. 00:06:40 At which point you can a send towards the brain. 00:06:44 Okay ipsilateral are across the white commissure and ascend contra laterally. 00:06:50 So again, this particular neuron traveled along the track of the Lissauer to synapse on a different level or segment in the spinal column. 00:07:00 Now, the same can be said for descending action potentials from other receptors and first order neurons in the same area. 00:07:11 However, what's going to happen as it comes towards the dorsal horn, it'll descent along the track of Lissauer. 00:07:17 And then synapse on second order neurons at that level again same thing it will ascend ipsilateral across the white commissure and ascend contralateral up towards the brain. 00:07:30 So again that the track of Lissauer allows innervation or the action potentials generated by receptors to travel several levels up or down, outside of their original site of the injury or the noxious stimulus. 00:07:48 Now clinically, this has some pretty profound application. 00:07:55 If in the event, some segment or level the spine or to be injured so let's say. 00:08:03 Use brown here, let's say this segment in particular on one side was damaged. 00:08:09 What's going to happen is that any kind of action potentials or information traveling at this level contralaterally or this little contralaterally will not travel to the brain. 00:08:20 However because of ascending second order neurons on the ipsilateral side of the spinal cord as well as those that have ascending along the track of Lissauer. 00:08:32 We are still going to get information no susceptive information let's say to the brain that we normally would not in the event that there is some sort of spinal cord injury. 00:08:42 So I'm hoping that clarifies a little bit about what the trackable Lissauer is and the importance of the tracking of Lissauer especially when we start considering clinical application. 00:08:53 As always, if you have any questions, reach out to me or Dr. Stern, and I will talk to you soon 00:09:00 [BLANK_AUDIO] 00:09:04 All right. 00:09:05 [BLANK_AUDIO] 00:09:06 We're going to go ahead and move on, if I can. 00:09:11 There we are. 00:09:12 So the takeaways. 00:09:13 The track of Lissauer is a pathway for first order neurons carrying light touch, pain and temperature information from the peripheral sensory receptors to the dorsal column of the spinal cord. 00:09:23 From any segmental level, this pathway can ascend or descend up to 3 segmental levels. 00:09:28 [BLANK_AUDIO] 00:09:31 As I said at the end of the video, please reach out to me or Dr. Stern regarding any of the content covered today, as this does conclude our lecture. 00:09:40 Thank you and speak catch you next time. cielo24 | what’s in your video? | cielo24.com 2.4 Conduction Illustrated 00:00:01 Hello and welcome to the lecture on Conduction Illustrated. 00:00:06 This is one lecture and a series of lectures on nociceptive conduction. 00:00:12 This lecture like the lecture on Lissauer's tract is slightly different because I am using a different medium of teaching material. 00:00:21 Namely, I am illustrating the information processing using markers [LAUGH] and paper. 00:00:30 So I'm hoping you enjoy and that it helps with your learning process. 00:00:33 So without further ado, let's get to our objectives. 00:00:36 [BLANK_AUDIO] 00:00:44 So the objectives for today, I would like you to be able to visually describe and draw the path of an action potential during nociceptive conduction, up to the pre-synaptic terminal at the dorsal horn of the spinal cord. 00:00:58 Right before we start, what this course identifies is the beginning of nociceptive transmission. 00:01:03 [BLANK_AUDIO] 00:01:09 Okay, so I am going to leave this part of the lecture up to, I guess, alternate me. 00:01:17 So let's go ahead and hear what he has to say. 00:01:19 [BLANK_AUDIO]. 00:01:22 Hello and welcome to another illustration of the nociceptive process. 00:01:29 This time, we are going to be illustrating conduction as a whole. 00:01:35 So as with any of my illustrations, I do want to start with a cross section of the spinal cord to give us some anatomical context. 00:01:47 So here we have, 00:01:49 [BLANK_AUDIO] 00:01:50 Okay, our cross section of the spinal cord 00:01:53 [BLANK_AUDIO] 00:01:55 All right, now with relation to the spinal cord, we have information that comes from our peripheral system that coalesce or come together at the spinal cord. 00:02:12 And when they reach a spinal cord, they travel up to the brain, okay? 00:02:17 So we're going to illustrate the initial steps, primarily transduction and conduction in this information processing system for nociception. 00:02:27 But this can also be applied to other kinds of sensory information, [COUGH] including light touch, or crude touch, and vibration, as well as some other sensory information. 00:02:38 So let's start from the beginning. 00:02:43 All right, our body responds to external stimuli through changes in chemistry. 00:02:51 If someone were to hit me, or if I were to bump a bone, or if I were to cut myself, the body would recognize that tissue damage, the release of different chemicals from damaged cells. 00:03:04 And the chemicals released from these damaged cells can include, most commonly, things like protons as well as other chemicals such as histamines and bradykinins and prostaglandins. 00:03:18 So when these chemicals start collecting around different receptors, sensory receptors in our body, the sensory receptors are activated. 00:03:26 And once activated, the sensory receptors will send action potentials to the spinal column, at which point they will ascend up to the brain. 00:03:37 Where we may eventually experience some sort of sensory experience, whether it be light touch or pain, again, depending on the stimulus. 00:03:48 So let's illustrate that. 00:03:51 So let's say we have a receptor over here, okay? 00:03:56 As a matter of fact, I'm going to use a different color because I don't want to blend in with the spinal cord. 00:04:04 So we have a receptor here and we have some tissue damage. 00:04:08 And from the tissue damage, we have different protons that are released, as well as some other chemicals, and it stimulates the receptor here. 00:04:17 [COUGH] Once this receptor is activated through transduction, it'll create an action potential, which will travel towards the spinal column. 00:04:33 At a certain point, it's going to enter the dorsal root ganglion, so we'll just make the dorsal root ganglion, okay? 00:04:40 And it will come into the posterior horn or the dorsal horn of the spinal cord. 00:04:47 At which point, it's going to synapse on a series of neuron cells as well as interneurons that will activate secondary afferent nerves or neurons. 00:05:01 Which will either, one, travel up to the brain ipsilaterally or will cross the spinal cord through the white commissure and then ascend contralaterally towards the brain, okay? 00:05:16 So there is one element to conduction that I think I want to illustrate, just because we've covered in the past, and that is, as I'm dropping markers here, is that, not all action potentials travel to one level of the spine. 00:05:33 Let's say given a certain number of peripheral nerves that are activated in a local area. 00:05:38 Some of them will travel several segments above or below the level of the action potential generation because of a tract called Lissauer's tract. 00:05:49 And if we were to, I have to pick up my orange marker that fell, if we were to look at this, let's say we have, I am going to do very poor illustration of [LAUGH] a 3D spinal cord dissection. 00:06:07 But let's say instead what's going to happen is that we have a receptor in the same area and it's been activated. 00:06:15 It's going to send information again through the dorsal root ganglion into an area just kind of posterolateral to the dorsal horn, and it's going to travel either up or down to different levels of the spinal chord. 00:06:32 At which point it will synapse on different cells within the dorsal horn of the spinal chord, and either travel ipsilaterally or contralaterally up towards the brain, all right? 00:06:48 So again, transduction and conduction are the first two steps of the information processing that's involved in nociception. 00:06:58 But again, this also includes other ways that we receive information about the different sensory stimuli that we interact with in our environment. 00:07:07 So to recap, we have injured a tissue, or some sort of stimulation to tissue. 00:07:15 That releases a series of chemicals, whether it be through the irritation of cell membranes and/or the lysine of cells, which release certain chemicals which activate these receptors. 00:07:27 And for our course in particular, these are going to be nociceptors, that is transduction. 00:07:32 Once this action potential is generated, it is sent through these primary afferent nerves, which are also called first order neurons. 00:07:43 They will travel along the first order neurons through the dorsal root ganglion and enter the spinal cord. 00:07:50 Now, again, some of the inputs coming from the periphery will go to the dorsal horns at the same level. 00:08:00 However, some will also ascend or descend the Lissauer's tract and activate different levels of the spinal cord along the dorsal horn. 00:08:08 And that input will then travel, ascend through the spinal cord via second order neurons of the sensory system. 00:08:19 So that is, I think, a very rough illustration of transduction and conduction, and I'm hoping that it helps you in understanding some of the content associated with this course. 00:08:32 As always, if you have any questions, I encourage you to reach out to me or Dr. Stern ,and I will speak at you soon. 00:08:39 [BLANK_AUDIO] 00:08:41 All right, fantastic. 00:08:45 So takeaways, primary sensory afferent neurons carry information from the periphery, primarily receptors that then take that information and send it to the dorsal root ganglia. 00:09:00 Or if we're talking about above the body, so the head, it's going to travel through the trigeminal ganglia for the head and face. 00:09:08 From the DRGs, the action potentials are going to travel to presynaptic terminals via Lissauer's tracts. 00:09:17 And then these presynaptic terminals are going to interface with the posterior gray horn or the dorsal horn in the body, or the spinal trigeminal nucleus in the thalamus for the head and the face. 00:09:29 Nociception can be very fast, [COUGH] excuse me, or slow. 00:09:33 And primary nociceptors are not necessarily slow conducting or small diameter fibers, as information for nociception can travel via A delta or C fibers, with A delta fibers being relatively fast. 00:09:45 [BLANK_AUDIO] 00:09:48 So that concludes our lecture on Conduction Illustrated. 00:09:53 As always, if you have any questions, please reach out to me or Dr. Stern. 00:09:57 Thank you and speak at you next time. 00:09:59 [BLANK_AUDIO] cielo24 | what’s in your video? | cielo24.com 2.5 Sensory Neuron Types Illustrated 00:00:01 Hello and welcome to our lecture on sensory neuron type illustrated. 00:00:06 This is one lecture in a series of lectures that looks to take a different approach to delivering content with respect to core concepts. 00:00:16 In this particular case, this lecture is going to look at sensory neuron types. 00:00:21 [BLANK_AUDIO] 00:00:23 Here's a slide on our pain declaration for this course. 00:00:28 [BLANK_AUDIO] 00:00:30 And here are the scaffolding objectives for this particular lecture. 00:00:34 By the end of this lecture, I hope that you will be able to visually appreciate the classification scheme for neuron types. 00:00:40 As well as draw the hierarchical anatomical relationship of ordered sensory neurons 00:00:45 [BLANK_AUDIO] 00:00:50 And without further ado, I'm going to go ahead and jump right into our video. 00:00:53 [BLANK_AUDIO] 00:00:56 Hello and welcome to sensory neuron types illustrated. 00:01:00 During this particular lecture, we are going to cover, and I should say review content from asynchronous lectures that have covered sensory neuron types. 00:01:11 The first thing I would like to review is our definition of a sensory neuron. 00:01:16 And that it is a primary afferent. 00:01:18 It's a type of pseudounipolar neuron that transmits sensory information from the receptors in our peripheral system to the dorsal root ganglion and eventually to the spinal cord. 00:01:32 Now, if you recall the structure of a pseudounipolar neuron is one where there's one axon that extends from the soma or the cell body of the neuron. 00:01:44 And it connects the periphery with our receptors to the central nervous system, which is going to travel through our dorsal root ganglia into the dorsal horn of the spinal cord. 00:01:57 So that is our pseudounipolar neuron, as well as the definition of a sensory neuron. 00:02:04 Now with regards to the classification schemes, there are four primary classification schemes that are used in literature. 00:02:12 One is the group, okay? 00:02:17 The next is the fiber. 00:02:18 [BLANK_AUDIO] 00:02:21 Next is the name. 00:02:23 [BLANK_AUDIO] 00:02:26 And that has to do with specifically what it encodes for. 00:02:32 So preferentially what that receptor is going to encode for. 00:02:36 And then finally, the order. 00:02:38 And again this refers to a hierarchical order and organization of neuroanatomy with regards to sensation. 00:02:47 [BLANK_AUDIO] 00:02:49 So let's start with our groups. 00:02:53 So the group classification system is a Roman numeral system where nerves are rated from I, II, III, IV. 00:03:10 And in some cases, there's five, but we're just going to refer to four. 00:03:14 Now the way this works is that this scheme has Roman numeral I rated as the largest and fastest type of sensory neuron. 00:03:27 And again, structurally that means that they're going to have more myelination than other fibers. 00:03:33 Now, this structure, this ordering scheme has the numbers indicating in order from fastest to slowest, and with that the myelination, 00:03:51 [BLANK_AUDIO] 00:03:53 Size. 00:03:54 So this is high on the myelination size here is relatively low, okay? 00:04:00 So again, this is going to be the group classification system for sensory neurons. 00:04:05 Now for fiber-type classification systems, these are much more widely used and I think recognizable. 00:04:12 We have A, B, and C categories, and then underneath that we have an inner class rating scale that's going to be from alpha to our delta, okay? 00:04:25 Now similar to the group classification system, the fiber type classification system is ranking the speed, as well as the structure of the neuron. 00:04:39 A, being your fastest and most myelinated, B, being faster than C, but slower than A with kind of moderate myelination, and C having most minimal, the smallest amount of myelination and consequently your slowest. 00:04:54 However, as noted in the asynchronous lecture, the C fibers are most commonly collecting sensory information, especially with regards to noxious stimulus in our body. 00:05:07 The inner class rating scale similar to A, B, and C are moving from your fastest type of neuron to your slowest type of neuron. 00:05:20 [BLANK_AUDIO] 00:05:21 Okay, now with regards to the name, specifically neuron names and this can be misleading as each one of these can be considered a name. 00:05:30 And what I'd like you to remember is that this classification scheme looks at the organization this neurons based on what best activates it. 00:05:39 So it's a name for what activates it. 00:05:41 For example, if you have a fiber that is activated by noxious stimulus so high-threshold stimulus, that can be considered a noxious sensory nerve or neuron. 00:05:55 Which brings us to our two categories of classification which is magnitude. 00:06:01 [BLANK_AUDIO] 00:06:05 As well as mode 00:06:06 [BLANK_AUDIO] 00:06:07 Now again the magnitude as it sounds is the amount of stimulus. 00:06:10 The more stimulus needed to activate a neuron, the higher threshold for activation that has, right? 00:06:17 And so, within our system, the high stimulus, the higher the threshold, the more potential harm it's going to have on our body and that's going to be considered a noxious stimulus. 00:06:29 And in keeping with this classification scheme, that particular neuron is going to be called a high-threshold noxious neuron. 00:06:36 As opposed to your non-noxious which are going to be your lower threshold receptors. 00:06:41 Whereby the body's going to pick up information from non-threatening stimulus such as vibration or light touch, or even proprioception, some movement of the joint. 00:06:53 That will eventually be experienced as, oh that is a comfortable nonthreatening stimulus so it's not going to be pain, okay? 00:07:00 So we have our noxious and our non-noxious. 00:07:05 [BLANK_AUDIO] 00:07:06 Now as far as mode is concerned, mode comes in three primary forms. 00:07:13 It comes in mechanical, temperature, and chemical. 00:07:16 And again, these are the types of stimulus that will activate certain neurons. 00:07:22 So there are neurons that are very sensitive to mechanical stimulus, there are neurons that are sensitive to temperature, and then there are neurons that are sensitive to chemical. 00:07:33 Now, of course, nothing is simple and in some cases, these receptors in our system these neurons can be activated by multiple modes. 00:07:43 And we call those receptors polymodal. 00:07:46 Within the literature, it is thought that mechanical type or mechanically sensitive neurons are often polymodal with temperature. 00:07:56 And so they would be considered poly mold and the fact that they are sensitive to both temperature changes, as well as mechanical changes. 00:08:05 In case of noxious neurons, so it's you have a noxious neuron that is mechanically sensitive. 00:08:11 Again, it's going to be responding to mechanical stimulus that meets a high-threshold of activation. 00:08:18 So we can have mechanical noxious neurons, okay, or we can have temperature non-noxious neurons. 00:08:28 And that really relates to comfortable sensations of heat or cold. 00:08:31 Ones where the body does not perceive that as damage or as a threat. 00:08:35 And certain circumstances of either immediate injury or prolonged injury, inflammation local to receptor can actually further sensitize these receptors and lowering the threshold for noxious stimulus. 00:08:51 So that in the event of additional mechanical or temperature stimulus, we can feel more for longer periods of time more intensely. 00:08:59 But again, we'll cover that in a different lecture aptly named both peripheral and central sensitization. 00:09:05 So those are our name classifications for neurons. 00:09:11 And finally, that brings us to order neurons. 00:09:15 Now if you recall, ordered neurons are a means through which we can organize neurons based on anatomy or looking at a hierarchical scheme. 00:09:24 And the names of these neurons are first, second, third, 00:09:32 [BLANK_AUDIO] 00:09:34 And fourth, all right? 00:09:37 And again this is order based on most peripheral to most central. 00:09:43 And our impulses are area information action potentials generated in the peripheral nervous system are going to travel in this order first, second, third, fourth. 00:09:52 Until eventually, if the stimulus meets certain criteria, we will experience a sensation, okay? 00:09:59 Now to illustrate that we are going to take, I don't know, let's take blue. 00:10:06 So blue is going to be our sensory receptor. 00:10:11 Here we have our primary efferent also known as our first-order neuron, okay? 00:10:16 So I'm going to go ahead and do mark this, this is 1. 00:10:22 Okay, so that is our first-order neuron. 00:10:24 And then it's going to come into our central nervous system, and within the central nervous system, as this neuron enters, it's going to go through the dorsal horn. 00:10:34 And at that level, this neuron is going to activate or turn on another neuron known as the second-order neuron. 00:10:43 Now, we're just going to call this whole nerve blue. 00:10:46 All right you know what Let's do a different color so you can differentiate between the different order neurons. 00:10:50 So at this level what typically happens with this information is that it's going to ascend right up the spinal column. 00:10:57 And it can either be ipsilateral or contralateral but for our purposes, we're going to go ahead and go to the contralateral side. 00:11:03 So it's going across the white commissure and it's going to go up. 00:11:07 So that's that second-order neuron and the second-order neuron is going to take information into the brain, up into the thalamus in particular. 00:11:18 And in the thalamus, it's going to go in to interact with the thirdorder neurons, okay? 00:11:28 And then from the third-order neurons, this is going to go into the primary sensory cortex or the somatosensory cortex. 00:11:38 And it's going to, 00:11:40 [BLANK_AUDIO] 00:11:43 Then interact with, let's go with the different color, let's go with purple. 00:11:47 I have so many colors here. 00:11:48 This third is going to come up and interact with our fourth-order neurons. 00:11:52 And as you can see, it is an anatomical hierarchy specifically organized from peripheral to central. 00:11:59 So what I'd like you to remember from this is that the first is going to be the beginning, the fourth is going to be last, just preceding our experience as symptoms or sensations. 00:12:10 First is associated with the primary afferent, and then following that second and third, really are conduits through which our information makes it through the spinal column. 00:12:21 Through the hein and mid-brain up into our primary cortex in the brain. 00:12:26 So I think that pretty much sums up what I really want you to be able to recall with this particular information. 00:12:34 I guess the only thing I would want to review are the primary efferent sensory neuron types, and we have four of them. 00:12:43 So this isn't just for nociception or for noxious stimulus, and I really want to make sure that's clear. 00:12:48 This is for all sensory information. 00:12:51 We have our A alpha, we have our A beta, we also have our A delta, and then finally, we have our C fibres. 00:13:03 These two categories here are primarily associated with the nonnoxious information. 00:13:09 So this is going to collect information specifically on mechanical stimulus for proprioception, as well as for light crew touch. 00:13:18 We really don't really get into nociception until we get these last two categories. 00:13:23 These A delta and C fibers, these are going to carry both non-noxious and noxious information, from our periphery. 00:13:32 With the C fibers in particular that being very diverse, they're going to be sensitive to mechanical, they're going to be sensitive to temperature. 00:13:40 And they're also going to be sensitive to chemical modes while the A delta can be more primary emphasize or emphasize activation for mechanical stimulus. 00:13:50 So that concludes our sensory neuron illustrated lecture. 00:13:56 I'm hoping that again this does clarify some points. 00:13:58 As always if you have any concerns or questions with this content I encourage you to reach out to Dr. Stern or myself. 00:14:04 Thank you and I'll speak at your next time. 00:14:07 Okay, fantastic. 00:14:09 Let's go ahead and move into the final slide if I can, our takeaways. 00:14:15 There are numerous classification schemes for neurons. 00:14:17 I would like you to be familiar with each type of classification scheme, as well as how they're differentiated. 00:14:23 And second, ordered neurons and sensory systems refer to a progressive architectural classification scheme of neurons carrying nociceptive input to the brain. 00:14:36 As I said in the other recording, [LAUGH] this concludes our lecture that looks at sensory nerve types illustrated. 00:14:45 If you have any questions, please reach out to Dr. Stern or me. 00:14:49 Thank you and speak at you next time. 00:14:51 [BLANK_AUDIO] cielo24 | what’s in your video? 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