Health and medicine
In this video, I review the somatosensory homunculus, which is basically a "topological" representation of the body in the brain. By Ronald Sahyouni. Created by Ronald Sahyouni.
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- Why do the hands and feet take up such a large part of the sensory strip?
Thanks in advance :)(10 votes)
- Because our sense of touch is finer and more detailed in our hands than on our back. This means that we need a larger part of the brain to process those impressions. There are also more receptive fields in the fingers than on your shoulders for example. This is because we use our hands for a lot of things, so having a very fine tuned sense of touch is very important. However, this is not only because of evolution. There is also brain plasticity! Experiments on monkeys have shown that stimulating certain digits of their hands will increase the size of the somatosensory homonculus for that particular digit.(18 votes)
- Why is it that sometimes where you feel pain isn't where the problem is? (for example, pain in the left arm when you have a heart attack)(5 votes)
- This phenomena is known as referred pain and it is not fully understood how it occurs and why it seems to happen in some individuals but not others. The main idea is that two different neurons on different parts of the body are converging onto a single dorsal horn in the spinal cord. This means that pain in the heart and pain in the left arm is detected by the same section in the spinal cord. The reason why the left arm sometimes feels pain before a heart attack is because the brain infers that the pain is felt on the skin on the arm that has neurons converging with the heart.(18 votes)
- What is the part of the Somatosensory Homunculus located in the area below the face? It was never talked about, and I can't really tell what the drawing is supposed to represent. Is it the tongue?(6 votes)
- Good question. Yes, it is the tongue and throat that are located below the face on the somatosensory homunculus. I suspect that the little sharp projection at the very bottom is the epiglottis.(7 votes)
- What would happen in case of a tumor in the sensory strip? Would sensations received from different parts of the body get amplified?(6 votes)
- Is the sensory strip the same as sensory homunculus ?(4 votes)
- Does the homunculus help explain phantom limb sensations? Why do people feel sensation in parts of their body that are no longer there?(2 votes)
- What happens is that in that area of your brain (cortical homunculus) for that limb, since it is no longer being used, the other regions around it take over (eg your arm)and then once those are stimulated, they may cause feelings in that lost limb.(1 vote)
- which part of somatosensory humunculus recieves pain from abdomen?
Suppose your friend pinches on your stomach(1 vote)
- If you pause the video around5:10, the abdomen (the entire trunk really) would be crammed in between the wrist section and the foot section - the abdomen isn't really used for feeling around the environment, so it doesn't require much attention to fine touch sense - this is why your back can withstand more pain than, say, your lips. Interestingly, the interior portion of the abdomen (what experiences a stomach-ache) is found below the tongue section on the lowermost left side.(2 votes)
- Why are areas such as the lips, hands, and feet drawn larger than areas such as the arms and legs?(1 vote)
- The areas such as the lips and tongue have more nerve endings per square cm. Therefore, the brain, in the somatosensory cortex, receives and recognizes more data from those areas. This is represented by the larger regions of the homunculus that maps the information from those nerve endings.(2 votes)
- What part is mostly represented on homunculus is it face or hand ?(1 vote)
- At4:28Ronald tells us that removal of a specific section of the sensory strip (in this case, the lip) would result in loss of sensation. Would this affect the motor function as well (I know the motor strip is separate but adjacent to the sensory strip)? More broadly speaking, how is the relationship between the sensory and motor strip's homologues affected with the removal of one another?(1 vote)
If you've ever used a map on your cell phone to get you from place A to place B, you're familiar with the idea that a map is simply a representation of some sort of area that actually exists in the real world. So a map on your cell phone is a digital map of an actual place somewhere in the world. Similar to this digital road map, your brain also has a map of your body. And this map is something known as the somatosensory homunculus. The somatosensory homunculus is basically a map of your body in your brain. And let me go into this because it is a little bit confusing conceptually at first. So what I've drawn over here is a picture of the brain. Let's just focus in on this pink area over here. This pink area is something known as the cortex. And this region that I shaded in in orange over here is a specialized part of your brain that receives sensory input from your entire body. So whenever you feel pain or whenever you feel some sort of heat anywhere in your body, all this information is actually sent through the spinal cord into the brain. And it all ends up over here in this one part of the cortex. And this part of the cortex is known as the sensory strip. So let me just clean this up a little bit. So if we were to actually take a cross-sectional look at the sensory strip, so if we cut the brain just right down the middle and kind of looked at it this way, what we would see would be this large orange structure that I drew here. So this orange structure is basically just the sensory strip. And we're looking at it this way if we cut it right down the middle. And so as I mentioned before, this sensory strip contains a somatosensory homunculus. And the somatosensory homunculus is basically a map of the body in the brain. And what I mean by this is that information that comes from your hand to the brain will all end up in one part of the sensory strip. So information from your finger will actually come over here. Information from these fingers will come over here. Information from the palm of your hand will come over here. Information from your wrist will actually end up over here in the sensory strip. And similarly, if we were getting information from your foot, the information from your foot would all synapse over here in this part of the cortex. And information from your toes would synapse over here. So you get the idea. Basically, information from various parts of the body will come into the brain, hit the sensory strip, and it will always go to one part of that sensory strip. So this is your face over here. So this would be the face. And so information from the lips would come right here, information from the eyes would go over here, and so on. So basically, the sensory strip always receives information from different parts of the body. And that information will always go to one part of the sensory strip. So let me again clean this up a little. If this is still a little confusing, let me try explaining it a different way. So let's imagine that there was a brain tumor right over here. This brain tumor would kind of look like this. It would basically be in this region of the brain. And so in order to figure out what part of the brain is tumor and what part of the brain is normal, neurosurgeons can actually go in with an electrode and touch different parts of the cortex. So they can actually come in, and touch this part of the cortex, and touch this part of the cortex. And this electrode will actually cause the cells that it touches to stimulate. And so in some cases, the surgery can actually be conducted on patients that are awake. And so if a surgeon touches this part of the cortex, patients can actually say, oh, I feel as if somebody is touching my wrist. And if the surgeon touches this part of the cortex, people might say, oh, I feel somebody touching my forehead or my eye. So depending on what part of the cortex the surgeon places his electrode, the patient will get a sensation of some part of his or her body being touched. The reason that surgeons do this is to make sure that they aren't removing parts of the cortex that are involved in sensation, because if the surgeon were to remove this part of the cortex, the patient would no longer have any feeling in the wrist or in the forearm. So they need to make sure that the part of the cortex that they're removing is not involved in sensation. Otherwise, the patient would actually lose sensation. Similarly, if the surgeon removed this part of the cortex, the patient would lose sensation in the lips because that is part of the cortex actually receives input from the lips. So let me again clean this up just to go over everything one last time. So the sensory homunculus basically maps out the body in the brain. So as information comes to the brain from different parts of the body, information from the hand will all synapse in this region of the cortex. Information from the face will synapse in this region. Information from the feet will synapse in this region. And so what this effectively creates is a topological map of the entire body in this strip of cortex. And this topological representation of the body in the cortex is what's known as the somatosensory homunculus.