Pacinian's Corpuscle and Merkel's Disk

The next mechanoreceptor is called Pacinian's Corpuscle. Pacinian's, this is another corpuscle. Another body we're going to talk about right here. And again, we'll have some external stimulus right here. Could be somebody poking you, or some other type of stimulus that's transmitted deep into our skin. Pacinian's corpuscle will respond. It looks like this. Also known as the onion-layered mechanoreceptor. You kinda tell why, right? Because there are a whole bunch of layers here. And another term for Pacinian's corpuscle is the Lamellar corpuscle. And lamella just means a layer. So there are many lamella around here. In fact that's an important term, so I'll write it here. So this is a Lamellar corpuscle. So, notice all of these layers here. What happens is that when we have this force transmitted deep into our skin. We'll have, say, this layer here. That layer will stay still, but the layer immediately outside of it that I'm outlining right here. So this outer force right here will cause this outer ring to respond by spinning. It'll turn this way relative to the inside disk. And compared to Meisner's corpuscle above. In order for this disk to move in this direction relative to this inner disk right here. We would require a little more significant of a stimulus. Something like a push or a poke to cause this disk to move relative to this disk. And it'll be the same thing as what we saw earlier with Meisner's corpuscle. When one disk move past the other, there's an opportunity for sodium to enter this ring. And this ring is also an epithelial cell that's been specialized. And they're all these concentric rings that lead into the middle. What do you think sits here, right dab in the center? Well, if you guessed an afferent nerve fiber, you are absolutely right. And so the sodium ions will go through between these rings or these epithelial cells to get to the center. And eventually, that would be a lot of sodium building up in this afferent nerve fiber. Thus generating an action potential that will be sent to our central nervous system. And so, if all this began from a significant stimulus, like a push. That means that Pacinian's corpuscle, likely perceives deep touch. And it's deep touch of hairy and non-hairy skin. An example of that would be what I drew up here. That's just going to be a poke. So, a very strong poke. Not like what you see on Facebook, but when someone actually pokes you in real life would cause this type of stimulus. And as we mentioned above with Meisner's corpuscle, we're going to have this exact thing here. And we're going to require constantly changing stimulus to keep on firing and sending a message to the central nervous system. And this makes sense, right? Because when we're taking the subway to work or school, and there's so many people that people have to be pushing and shoving to fit in one car. You won't even notice if someone's pushing against you after some time. And finally, if this is going to be a significant stimulus that perceives deep touch, we can deduce then that Pacinian's corpuscle would sit lower than Meisner's corpuscle. And sure enough it's found deep in the hypodermis. Or the subcutaneous tissue sometimes. So it's pretty deep there. As we move further along, we can talk about the next mechanoreceptor that is called Merkel's disk. So, Merkel's Disk. We've been talking about corpuscles all this time. But now we'll just talk about a single disk. And our stimulus will be the same. If we have some type of external force right here that pushes and transmit this force deep within our skin, we'll have Merkel's disk respond. I don't have a fancy picture for it. And that's because Merkel's disk is actually just a specialized keratinocyte, or an epithelial cell that's not unlike the regular cells you have in your epidermis. So, it kinda sits in your epidermis. So, it kinda looks like this. This also has an afferent nerve fiber that sits right there. And the reason why we have all of these little vertices right here is because Merkel's disk holds a whole bunch of vesicles. You might remember that term, vesicles. Which are just pockets that have membrane around them that's sitting within the cell. These pockets hold a neuropeptide. So I'll draw a little neuropeptide in each of them You've probably heard of neuropeptides before, but it's just a peptide, which is a string of amino acids that talk to the nervous system. This is a neuropeptide sitting within our vesicle in our specialized epithelial cell, the Merkel's disk. And what I'll draw down here is a little receptor. This is going to be an "n" be a neuropeptide. "Np" receptor, just to abbreviate. And what will happen is that when we have this force transmitted right here, it actually causes the vesicle to open up. And so this kinda splits open right there. It allows the neuropeptide to be liberated. It's going to be present within the cell, kinda floating around. And, over time it'll come and sit down right here. And when it lands on the neuropeptide receptor, we'll actually start having ion channels open. So, ion channels should signal sodium. Ion channels will open that allow sodium to enter Merkel's disk. And eventually make its way into this afferent nerve fiber. And that generates the action potential that'll go communicate with our central nervous system. And with Merkel's disk, this is just a specialized keratinocyte or an epithelial cell. It's just like what we have sitting in our epidermis. So much so, that it's located itself in the epidermis. It's found in the stratum basale. Or it can be even lower, in the papillary dermis. So I'll write two here to emphasize it's in between these guys. So the trick is that if you remember that this is a specialized keratinocyte, like what's in the epidermis. You remember then that it sits pretty high up in the stratum basale to the papillary dermis. And so it's responsible for perceiving light touch. Light touch, this is gonna be on both hairy and non-hairy skin. But it's different from Meisner's corpuscle, because this is sustained light touch. So this is something that is going to keep on firing as long as you have the stimulus present. And that makes sense, because when the stimulus is there, and it's causing this sensation, as long as the neuropeptide is connected to this receptor. We're going to keep on having these ion channels open. And the sodium coming in, and generating the action potential. And remember, it's sustained light touch. As long as the stimulus is there, we're going to keep on noticing it.