Gtgt This is a preview tutorial on the spinal cord. We’re going to cover pathways and our general senses. This is lecture 12. The learning objectives that we’ll cover are the structure of the spinal cord. We’ll cover a couple of pathways that go to and from our brain. We’ll talk about our general senses like touch and pain and itch. We’ll talk a little about reflex arcs and then finish up with a little bit about referred pain, when our brain gets confused when we get pain signals. Describe the basic structure.
And organization of the spinal cord. It’s all about wiring. So when you think of the spinal cord, it’s really just a specialized bunch of wiring and so that’s what that little spinal cord is. Neurons and their axons, our wiring and it’s protected by the vertebral column. So all those vertebrae stacked on there have that vertebral frame in where we had room for our spinal cord. The wiring goes up and down and of course has to have attachments that come off of it. So if we look, we can see spinal nerves.
That come off each level of the spinal cord and they actually come out between the vertebrae. We also will talk about cranial nerves more in lab. Cranial nerves come directly off the brain. When our spinal nerves come off, they form often a complex plexus which are a network of nerves and then they give off nerves that we often name, like the ulnar nerve or the musculoskeletal nerve or radial nerve. So if you’ve ever seen wiring like this in your house or in a computer or somewhere at work, you know.
BIO160 Preview Tutorial Lecture 12 Sprinal Cord and Senses
That it’s messy. And so luckily our spinal cord and our wiring system is very organized so we can have sets of afferent wiring, again, when I say wiring, I’m talking about the axons from that various neurons. We can have efferent wiring. We can have wiring that’s separate for our arm versus our leg. We can have wiring that’s separate based on function. So we could have our skeletal muscle efferent wiring separate from our autonomic efferent wiring. When we look at our sensory wiring, we can have our temperature,.
Our pain, and our touch wiring. Our axons and neurons separate. And again, so we’re very organized. In this diagram I though you could almost say that this bundle here would be your spinal cord and some of the, all the various wiring we see in our spinal cord. And then we could actually see and take this away and see how our nervous system is sort of hooked up to our spinal cord. So you might have some wiring away from the spinal cord and to the spinal cord. In this case,.
We’ve drawn some skeletal muscle wiring and some pain wiring. They’re beginning in the attachments to the spinal cord are called roots and the roots are actually not mixed. So they’ll be separate wiring from say, efferent and afferent. As the wiring moves away from the spinal cord, it actually becomes mixed in the plexuses and the actual nerves and spinal nerves that come off the spinal cord. So some of our wiring is mixed and some is not. And you could see here, once you get out to your peripheral spinal.
Nerves and peripheral nerves it’s mixed in terms of temperature, touch, pain, muscle and the like. We’ll learn more about this when we talk about the specific organization of the spinal cord. But you’ve got the spinal cord, you have roots, you have actual spinal nerves, which come off of those roots and then you have nerves that we name in the periphery. If you actually look into your spinal cord within your vertebral column, again, it’s nervous tissue and one thing you’ll notice is that it’s protected by the various parts.
Of our vertebral column, including the sacrum and so that spinal tissue must exit the bone. One weird thing or interesting thing is that the spinal cord proper ends at about the level of L1, L2. Now they’re still nervous tissue in that canal, it’s just long roots. And so that’s an area where the actual spinal cord proper has ended there. We can name our spinal cord and our spinal nerves based on cervical, thoracic, and lumbar region. Just like we do the bones. So if you stack up those bones,.
Of course you add some cartilage padding in there. You can see to the posterior side would be your spinal cord and then exiting between the spaces between the bones, are going to be spinal nerves. And so the way you name your spinal nerves sort of depends on the bone. So for much of the spinal cord, we need the spinal nerves as they exit underneath the vertebra. So T5 bone would have T5 vertebrae exiting right below it. Once those spinal nerves come out of your spinal cord, they create plexuses often.
And then they go to nerves that we name. And so for example, this could be the cervical plexus, which would give off various nerves. This down here could be the sacral plexus, which gives off, again, various nerves. One of the famous ones is the sciatic nerve. The sciatic nerve could then branch into things like the tibial nerve, etc. and go to things like, say, your gastrocnemius. We have some other famous plexuses. The brachial plexus and the lumbar plexus. Again, they’re named based on where they’re exiting from the spinal cord.
The thoracic region really doesn’t have many plexuses, so it’s more of a simple wiring system up there. So again, we’re talking about as we exit the spinal cord. So if we look at the spinal cord, it’s all just wiring. If we cut through the spinal cord we can see now a perfect, nice section of any, you know, assume anywhere in your body but we’ll look at the spinal cord. We see have a right and a left side of our spinal cord. We are controlling things, right The spinal cord is getting.
Wiring out to control things. So here is wiring going out to your skeletal muscle. Don’t forget it uses ACH to contract that skeletal muscle. The wiring for our skeletal muscle is in the ventral part or the anterior part and so we call that where that originates the ventral horn. Then those wires go out through what’s called the ventral root and then that ventral root eventually becomes a spinal nerve. And so that’s your efferent wiring. Your afferent wiring goes a little different. So if we follow say a touch.
Or a pain neuron from your skin, so we’re just redrawing the muscle one. But if we look at our skin and we look at say sensation for touch, the wiring goes in that same spinal nerve but then it branches off and it goes in what’s called the dorsal root and then it goes to what’s called the dorsal horn of the spinal cord. So that dorsal root is actually just afferent wiring. So the roots as they attach to the spinal cord are not mixed. The motor and sensory are.
Separated out. That’s kind of interesting. Versus the spinal nerve plexuses and nerves that go to our actual skin and muscles are mixed. So just some vocabulary. Ventral horn, dorsal horn, ventral root, dorsal root. So it’s all about organizing the wiring. So our motor wiring, especially by our spinal cord, is separate. The autonomic versus somatic wiring is separate. Visceral versus somatic, again is separate. Arms and legs may be separated out as well as they axons travel in your spinal cord. What is few wanted to wire up something like our heart.
So remember the heart would be autonomic nervous system, which is a motor system because it controls the muscle but it’s a separate one from what controls your skeletal muscle. So it’s a slightly different wiring, both in the spinal cord and where the roots go off to. So shown here comparing it to skeletal muscle. So slightly separate wiring. Again if you were having sensation from your heart, that wiring would go together with the nerves and then all of a sudden branch off and go with the sensory side of things.
Which is the dorsal root and the dorsal horn. Same with your skin wirings. Somatic sensory goes more dorsally into the spinal cord and then tracks run up and down your spinal cord for these different wiring systems. Autonomic, sensory, motor, skeletal, pain versus touch. And so keep that in touch. When we learn about the autonomic nervous system, I think next week, we’re going to talk about the wiring of the autonomic nervous system. So I just wanted to point out that they actually come off of different parts of your nervous system.
The parasympathetic nervous system comes off cranial nerves and also sacral spinal nerves. And it wires up your organs again that your nervous system control but you don’t actually consciously, voluntarily control. Your sympathetic nervous system is wired up to those same organs but the wiring comes off the thoracic and lumbar spinal nerves. So it comes down your spinal cord and then the wiring shoots off the thoracic and spinal regions. There’s also some nerve plexuses in your abdominal and thoracic cavity. So something like your stomach will have sympathetic wiring.
And parasympathetic wiring and they just come from very different regions of your anatomy. So keep that in mind. When we look at the spinal cord it’s important to remember that the connective tissue, meninges, and CSF protect the spinal cord too as well as the brain, which we learned earlier. So we have things like the dura mater, arachnoid matter. So just as some orientation here we’ve got our spinal cord surrounded by the vertebral bone. We’ve got that spinous process to the back or posterior. We’ve got our back muscles,.
Say our erector spinae muscles. And so then we can see our dura matter, actually labeled that should be roots. So if we look, the spinal cord gives off those roots where those roots become the spinal nerve and so just to orient yourself there. There are the roots. There are the ventral and dorsal horns. So let’s look at those meninges. So the dura mater, arachnoid mater, and pia mater are again, the three layers. The CSF is sandwiched between the arachnoid and pia. The CSF helps cushion your spinal cord.
But we also have some fat, adipose tissue and some connective tissue in there between the bones periosteum and the dura mater which creates the epidural space. The epidural space, again, is cushion and now doctors and nurses and nurse anesthetists, people take advantage of this. They can inject drugs into the epidural space which will sort of diffuse and seep into the spinal cord and block that nervous tissue. So that would be an epidural. You would not want to inject into the CSF because then that drug would go up and down.
In your CSF, even to your brain and so that wouldn’t be so good. In lab we will talk about if you want to sample the CSF, then you would actually want to put that needle through the dura through the arachnoid and pull out a little bit of CSF. What about pathways So there are many pathways to and from the brain. We’re going to cover a few. So again, pathways we’re talking about spinal cord pathways that go up and down, either to our skeletal muscle. So down to our skeletal muscle.
Or coming up from our various senses. So we’ll talk about those. Motor commands, obviously our efferent so we can call them efferent or descending. Sensory signals are ascending so we can also call those afferent. So we’re going to cover pathways. We’re going to cover one pathway that controls your skeletal muscle and a couple of pathways for things like pain, touch, and temperature. So this first pathway we’re going to learn is the corticospinal pathway. It’s to control your skeletal muscle so it’s actually voluntary control of your skeletal muscles.
It links up your primary motor cortex and cerebrum to your skeletal muscles in your limbs, arms, and legs in your body with just two neurons. So I think that’s kind of amazing that it takes just two neurons. So let’s look at our corticospinal tract. Again, it’s descending. It’s efferent and the signals are going to go down to our skeletal muscle. Those signals are going to originate up in our primary motor cortex. So remember your primary motor cortex is in that frontal lobe, right there next to where the parietal lobe is.
So that’s your left primary motor cortex shown here. And it would send neurons down your spinal cord to control your arms and legs on the right side. It would also send some signals out to control things like your face as well. That wouldn’t have to go down with the spinal cord. So here we go. We go from our primary motor cortex on our left side. We’re going down and in the medulla, that neuron axon then crosses over. So again, it’s still the one neuron, run all the way.
Down from our brain down to our, in this case, our spinal cord and lumbar region. So these are called upper motor neurons. So the upper motor neuron goes all the way down, crosses over in the medulla. The lower motor neuron then exits our ventral horn in our spinal cord and goes to our muscle. So that’s called a lower motor neuron and it releases the acetylcholine to control the muscle. It tells your muscle to contract. Alright so it just took two neurons to go from our left primary motor.
Cortex to our right muscle. Let’s say in our right quadriceps and tell it to contract. Or in this case, I wrote move my hand. Let’s say move your leg. What if you wanted to move your face and smile Well it’s not the corticospinal tract but very similar in the same way in that your brain, your primary motor cortex sends out a signal, probably goes to your brain stem, synapses with another neuron and then that neuron goes out say your zygomaticus major and causes your facial muscles to contract.
And those are called cranial nerves when they come directly off the brain. So the zygomaticus major is controlled by the facial nerve. So again, if you want to wire up the left side of your body. It would come from the right side of your brain. I’m just reminding you of that again since this is motor control of muscle. It’s going to involve our ventral horn and our ventral root before you get to the mixed nerve which carries those signals to the muscle. So right brain control left side.
If you have a right brain stroke, you’ll potentially lose control of your left sided muscles. So your right brain would control your left leg and your left arm. Spinal cord injuries are sort of interesting. So remember if you injure your spinal cord, all the nerves below the injury will not be working. Will not be carrying signals. So skeletal muscle below that injury or sphincter muscles below that injury made of skeletal muscle, will no longer receive signals and will no longer work. So you might lose control say.
Then of your legs in that case. If the nerves that go to your arms are above the block, then your arms would be okay. The skeletal muscles would still receive signals and your arms would still work. So it really depends where the level of your spinal injury is. The worst would be up in the cervical region, because you would lose function of your arms and legs. Also, possibly, breathing because your diaphragm is skeletal muscle and needs nerves to control it. We’re going to show a tutorial in class of this football.
Who developed ALS or at least ALS like symptoms. Sometimes this is called Lou Gehrig’s disease and it’s a disease of the corticospinal tract. And the upper motor neurons degenerate. So those upper motor neurons that control your muscles degenerate and in this case, Steve Gleason lost control of his arms and legs, partially. And potentially you could lose your ability to breath and that would obviously dangerous. He eventually lost his bility to speak. So again, that’s a disease of the corticospinal tract that we just learned about. We’re going.
To learn two ascending pathways, which mean afferent stuff going up. The first one is called the posterior column and it’s involved in touch. And the second one is called the spinothalamic tract and it’s involved in pain and temperature. And we’re going to go through both of these. Both of those take just about three neurons to go from say your fingertip all the way up to your brain, your primary sensory cortex. So again, it’s pretty amazing how few neurons you need to get these great, large distances. So again, posterior column is an.
Afferent, ascending pathway. It’s mostly for touch, proprioception. So awareness of your body position. The destination of these signals is going to be our primary sensory cortex, which is in the parietal lobe. So that’s where we’re going to get our signals going. You have one on your right and left side of your brain. So let’s say you’re going to touch your foot and I think we’re touching our left foot here. So you touch your foot and again, the signal is going that dorsal root into the dorsal horn.
The cell bodies are actually located in the dorsal root ganglion. So remember that’s just a little pouch or enlargement of the dorsal root and that’s where the cell bodies of all your sensory neurons are. No matter where they are. So we’re then going to go up and we go up to our medulla and we’re going up in the posterior part of our spinal cord. The medulla is the crossover point now for this information in this wiring system. So we’re crossing over in the medulla oblongata. We take another neuron now.
And we go all the way up to the thalamus. You guys remember the thalamus is the relay station or sensory relay station for most senses that reach your awareness in the thalamus. We’re going to take another neuron and finally end in our sensory cortex. Since this was our left foot, we’re going to go to our right sensory cortex from our left foot. And so eventually those signals would reach your consciousness and you go aha, I just touched something. There are so proprioceptive signals that go directly to your cerebellum.
Remember we talked about the cerebellum. That would be a little bit different than this posterior column. But you do have sensations from say your knees, your joints, and things that actually will give you awareness of your body position. That proprioception will reach your cerebrum and your cerebral cortex. So that’s the posterior column and it is involved, or posterior pathway if you want to remember it as that, that’s involved in touch and proprioception. Spinothalamic tract, again, is an afferent, ascending pathway. It’s going to involve or relay pain.
And temperature information to your brain. Maybe even some itch as well and crude touch. So ouch, you step on a tack. It’s very sharp. It hurts. So now we’re going to generate action potentials which go through wiring in a neuron that goes through our dorsal root to our dorsal horn. Now this wiring system crosses over in your spinal cord and then goes all the way up to your thalamus. Again, the thalamus is the sensory relay area, relay station. And then the next neuron will carry that to your primary.
Sensory cortex. Again, on the opposite side because we’ve crossed over now this time in the spinal cord. So left pain goes to the right brain. Again, into that primary sensory cortex. When your brain actually interprets the pain signals coming in, that will involve that sensory association area where you go oh that’s a needle or that’s glass. Also your hands would be wired up to a similar but different area in your right brain as well. And so again, the left sensory cortex would get signals from the right brain.
If you had a stroke in your left sensory cortex, you would have numbness or loss of sensation from the right side of your body. So that’s the spinothalamic tract pain and temperature. Touch again, posterior column. That goes up in a different wiring system. It goes from your foot. It crosses over in the medulla. It goes up the spinal cord in a different area and then eventually reaches slightly different areas in your sensory cortex. So it’s all about organization and wiring for your spinal cord and these pathways.
Yeah I think I’m drawing in here the control of muscle. Again, that would be your corticospinal tract and that wiring would be separate and very different, both in the brain and the spinal cord as well. So that’s the wiring. Those are the pathways we’re going to learn. Explain the mechanisms responsible for your general senses such as touch, warm, cold, hot, pain, tickle, itch, and proprioception. So we consider those general senses compared to when we’ll learn later, like vision, hearing, and balance. So all of these general senses,.
Many of them are going to originate in your skin and that’s where we get a lot of our somatic senses from. And it turns out they have neurons wired up to your skin and the various neurons will sense or detect different versions of these. So some will be able to detect hot. Some will detect pain. And so we want to understand how is that possible. So here you have, imagine your finger with your skin, with two sensory neurons. Pain is caused by damage to your cells and they release chemicals.
Those chemicals can activate then receptor proteins in your dendrites of your sensory neurons. Once activated by these chemicals, they open up and sodium and calcium can rush through these little protein channels which causes depolarization inside our little cell, inside our little neuron. And that then causes voltage gated sodium channels to open up. So remember, they’re responsive to that positive charge. They open up, sodium rushes into your neuron and as those little positive rush in there, sodium rushes in, we’re generating an action potential. And so you’re getting an.
Electrical impulse now that would go back to your brain and your brain will interpret that damage and that pain as ouch. You can also have a neuron shown here that’s receptive to cold. So it actually makes little proteins that change shape depending on the temperature. When they get cold, they open up. Sodium and calcium rush in. That causes depolarization. That triggers the opening of these little sodium channels. Again, in the neuron they’re normally closed. Then they suddenly open up. Sodium rushes in because of the cold, starting the action potential.
And you get an action potential which goes back towards your brain and of course your brain will interpret this as cold. So that’s basically how your senses work. Now where is it being sent How does your brain know it’s your foot and not your hand Well you’re wired up to your brain to your foot. You have a brain that’s used to getting signals from your foot. When it get signals, it knows then my foot is feeling the touch. What about the modality How do you know is it hot, cold,.
Touch, temperature Well, again, certain neurons are responsive to certain stimuli and they are wired up to specific parts of the brain. So this brain region knows warm and temperature and another brain region will know touch. So it’s sort of this labeledline, the fact that your brain is wired up to certain areas and then the brain interprets it that way. When they did that open brain surgery, if you were to zap the brain in a specific region, it might say, Hey, you’re touching my face. Or you feel cold on the face.
And that’s because that’s what that brain region is dedicated to. You zap another area of the brain and someone might think, Ouch, you’re touching my lip. Again, you’re not really touching the hand or the face or the lip but that’s what the brain is wired up for. So when you stimulate that part of the brain, it interprets it that way every time, even if you’re just poking the brain. Let’s look at this. Imagine you have the skin and the skin is wired up to four neurons, four sensory neurons.
And so if we look out at the skin, we find that the first neuron is responsive to cold, the second neuron is responsive only to warm, the fourth neuron is responsive to pain and really cold pain and the third neuron is responsive to touch. So how is that possible How can we get neurons that respond to only one stimulus So if you damage your skin, neuron four fires an action potential. If you touch your skin, neuron three fires an action potential. If you warm the skin, number neuron two fires.
Action potentials. If you cool the skin, neuron number one fires action potentials. How is that possible How can each neuron only detect one or maybe two different stimuli or sensations And that troubled people for a long time. We didn’t always have answers to that. And then later, people discovered that each neuron at the dendrites expresses different proteins. And so those little dendrites are what are actually out at the skin. And so for example, the cold neurons produce protein channels that respond to cold. The pain neurons produce.
Proteins that respond to chemicals in damaged tissue and damaged cells. The warm neurons made a protein that’s responsive to warm temperatures. And then some neurons respond to multiple stimuli. They may make one or more proteins that can respond to say, cold, and pain. So that’s basically what they found that happens is that the different neurons make different proteins. Remember your genes determine your proteins because they have the instructions so these neurons are going to their instruction book and making simply different proteins. The cold neurons are going.
To the instruction book and making the cold protein. The pain neurons are going to the instruction book and rather making the pain proteins. And they’ve discovered some of this by making mutual mice. So you can change the DNA of a mouse so it can’t make the cold proteins and it can’t make the cold proteins so it really doesn’t care about cold. I mean it might care about it, but it can’t sense it. It can’t sense cold in its paws because the DNA was changed and the neurons then don’t.
Respond to cold. But it still responds to pain, other neurons respond to pain, touch, and warm. And so that looks more like a cat than a mouse. But what do those receptors look like Little channels. Some of them are channels themselves for sodium and calcium. So when it gets cold, the little sodium calcium channel opens which then triggers an action potential in the cell, in the neuron. And then by sodium rushing in, it will only respond to cold and the nearby touch neuron won’t respond to the cold.
Because it doesn’t have the right proteins. If you touch those neurons or touch the skin, the end of those neurons, the touch neuron, the little channels, will open up due to the deformation of the skin and sodium will rush in and you get an action potential. But the cold neuron won’t respond because its little proteins don’t respond to touch. So it’s kind of interesting. A few notes on pain. So pain is something we’ve all experienced. So pain is usually due to damage locally in your skin or tissue and that causes action.
Potentials in neurons, right Then that would be part of the spinothalamic tract. So we can block those pain signals either locally by numbing say, the fingertip with a chemical or we can apply a more global block, say an epidural, a drug right outside that epidural space, which seeps into your spinal nerves in your spinal cord. You also get things like pinched nerves and herniated discs which can smoosh your nerves and you’ll start getting signals going up to your brain. Your brain will interpret that as pain, even though you’re not really.
Having pain perhaps in your leg. You’re actually having pain up near your spinal nerves in your spinal cord or one of your nerves going to and from your hand. Again, so you’re not actually necessarily having pain in those cases if you have an herniated disc or a pinched nerve, but your brain will interpret it the same way as pain. So pain is something that is actually good. It warns us that there is damage going on. So you need pain to let you know that something bad is happening.
Pain signals include histamine and potassium, prostaglandins, these different chemicals which will activate neurons. Some pain signals can be blocked by opioids. So opioids are strong painkillers. They actually cause neurons in your spinal cord and brain to stay or are polarized to stay negative so that they don’t send pain signals back or interpret pain signals back in your brain. Local anaesthesia would be like the dentist numbing your nerve or an epidural. Versus opioids which target your brain and spinal cord by taking a drug and ingesting a drug.
And of course you know painkillers like Advil and aspirin, they can decrease some of those pain chemicals that simulate the pain neurons. Is itch a pathway So we have all experienced itch before and more recently, they’ve actually determined that actually humans and animals have pathways and neurons dedicated just to itch. And histamine is one of these chemical which really likes to activate those neurons and then you feel the sensation of itch and maybe instead warn you that you should scratch your skin to get an insect off.
Or something like that. Of course you know sometimes with allergies it seems like that whole system goes haywire. Another thing you’ve probably experienced is when you stub your toe. You probably feel the stubbing first and then you might get a sharp pain next and then finally, you’ll get a dull ache. It’s because some of these signals travel faster. Myelinated neurons and myelinated axons carry the signal faster. And larger diameter axons carry signals and action potentials faster. So things like touch are very fast conducting axons. Sharp pain is pretty fast too.
Versus dull pain is kind of slow. So that’s why you’ve experienced that. I just wanted to mention as well about proprioception. Proprioception is this awareness of selfposition. Even if you close your eyes, you can kind of tell where you’re limbs and hands and your body is positioned in space. So you just have a feeling of where you are in space. And these are actually afferent signals that would similar to touch that are coming from things like your tendons, your skin, your ligaments, and then go up to your brain.
And then your brain processes that as proprioception as where am I in space You do not get proprioception from your kidneys and your heart and your internal organs. You don’t really know where your kidney is unless a textbook or somebody tells you. So you don’t get proprioception from your organs. So the next learning objective, I wanted you to understand a little about reflexes. A reflex is an involuntary patterned response and again, it’s going to involve our nervous system. So if you hold your finger or touch your finger.
Over a hot flame, you’ll immediately withdraw your finger. And this is an example of a withdrawal reflex. So you get a pain neuron activated by the flame, again damage to the tissue there activates the pain neuron. The signal goes up to your spinal cord to a little relay neuron called an interneuron and then a motor neuron will carry a signal out to a muscle on your hand or your arm. So you get the pain signal, it goes to the interneuron and then it immediately tells your muscle to contract.
All that happens before you even notice. So it’s this involuntary patterned response to the flame. Before you’re even aware of it because the awareness has to travel up your spinal cord through in this case, the spinothalamic tract, up to your brain and then you become aware that you just touched a hot flame. So that’s an example of a reflex. Here’s another example of a reflex that doesn’t involve your spinal cord but it’s very similar. So you’ve all experienced this where you shine a bright light on the eye or you go outside.
And it’s bright and your pupil gets smaller. And that’s due to change in size of this thing called the iris. So here’s the wiring for you to actually be able to see vision. It goes from your retina, the back of your eye, through the optic nerve, eventually reaching your occipital lobe. But there’s also this sort of shoot off or sort of side pathway, where those same signals go to your brain stem and your brain stem senses the light as well and your brain stem then controls your iris.
And it controls it through signals to the smooth muscle of the iris. And so that will constrict your pupil and that will happen even before you see it because that’s a reflex. That’s a different loop or arc. It goes from your optic nerve to your brain stem and out to the iris versus going the same signals can go back to the thalamus to your visual cortex and your occipital lobe and you actually see the light. So just to give you an idea a little bit about reflexes.
That we’ll talk about and you may have heard about. This one just involves the brain. It didn’t involve the spinal cord. Compare visceral sensory information versus somatic sensory information. I wanted to talk a little bit about referred pain. So imagine your heart hurts versus your skin hurts. Remember we said that skin, we’re always aware of our skin. We call that somatic sensation. Versus your heart and stomach. We usually don’t get signals from there so we consider those organ sensory information visceral. So visceral sensations versus somatic sensations.
All of that information goes up to your brain and then your brain interprets, you know, what am I feeling Am I feeling stuff from my skin or my heart And sometimes we can confuse the brain. So let’s imagine we’ve got our spinal cord here wired up to our heart and our skin. And so in the case of referred pain, let’s make our heart hurt. So you have a heart attack. You have a blocked coronary artery and you get a myocardial infarction, a fancy word for heart attack.
Tissue dies and there’s damage which activates pain neurons coming from the heart. Those pain neurons go the similar way, the dorsal route, to the ventral route and up to your brain. Similar to the wiring you would have from your skin. But in this case, our skin is not hurting but our heart is. So all these signals go up to your brain and your brain has to interpret the signals so it’s getting signals from your heart and it interprets those signals and in the case of heart hurting,.
It often will mistake those signals as being from the skin. Maybe it’s because it’s a new sensation and it mistakes it for what it commonly gets which would be skin sensation. So again, referred pain is very common from various organs. In the case of a heart attack, you’re actual heart is hurting. Sends signals up but your brain interprets it like, oh my left arm is numb, or my left arm hurts. Again, why is that happening The skin and the heart are sending up their signals through similar areas.