What is a Pacinian corpuscle and how does it work? Need help with Biology? One to one online tuition can be a great way to brush up on your Biology knowledge. Answered by Martin L. Thus, the fingers, which require the ability to detect fine detail, have many, densely-packed up to per cubic cm mechanoreceptors with small receptive fields around 10 square mm , while the back and legs, for example, have fewer receptors with large receptive fields.
In general, these neurons have relatively large receptive fields much larger than those of dorsal root ganglion cells. However, the neurons are able to discriminate fine detail due to patterns of excitation and inhibition relative to the field, which leads to spatial resolution. The relative density of pressure receptors in different locations on the body can be demonstrated experimentally using a two-point discrimination test.
The subject reports if they feel one point or two points. If the two points are felt as one point, it can be inferred that the two points are both in the receptive field of a single sensory receptor.
If two points are felt as two separate points, each is in the receptive field of two separate sensory receptors. The points could then be moved closer and re-tested until the subject reports feeling only one point. The size of the receptive field of a single receptor could be estimated from that distance. Thermoreception is the process of determining temperature by comparing the activation of different thermoreceptors in the brain.
Describe the various types of receptors used for thermoreception: Krause end bulbs, Ruffini endings, free nerve endings. Thermoception or thermoreception is the sense by which an organism perceives temperatures. The details of how temperature receptors work are still being investigated. Mammals have at least two types of sensors: those that detect heat i. A thermoreceptor is a sensory receptor or, more accurately, the receptive portion of a sensory neuron that codes absolute and relative changes in temperature, primarily within the innocuous range.
The adequate stimulus for a warm receptor is warming, which results in an increase in their action potential discharge rate; cooling results in a decrease in warm receptor discharge rate. For cold receptors, their firing rate increases during cooling and decreases during warming. The types of receptors capable of detecting changes in temperature can vary.
Some of the receptors that exhibit the ability to detect changes in temperature include Krause end bulbs and Ruffini endings. Krause end bulbs are defined by cylindrical or oval bodies consisting of a capsule that is formed by the expansion of the connective-tissue sheath, containing an axis-cylinder core.
End-bulbs are found in the conjunctiva of the eye, in the mucous membrane of the lips and tongue, and in the epineurium of nerve trunks. They are also found in the penis and the clitoris; hence, the name of genital corpuscles. In these locations, they have a mulberry-like appearance, being constricted by connective-tissue septa into two to six knob-like masses.
Krause end bulb : A drawing of a Krause end bulb receptor which can detect cold. The Ruffini endings, enlarged dendritic endings with elongated capsules, can act as thermoreceptors. This spindle-shaped receptor is sensitive to skin stretch, contributing to the kinesthetic sense of and control of finger position and movement. Recent work [ 23 ] has found that using a low modulus for the lamellar stiffness gives more accurate predictions of PC response in the high-frequency range, but collagen fibers have been found to have moduli in the MPa range [ 25 ], as have basement membranes from the renal tubule [ 26 ] and ocular lens [ 27 — 29 ].
It is thus clear that a better theoretical and structural description is needed, and it is likely that the choice of modulus will depend on the structure of that model. Since the emphasis of this work was on the effect of anisotropy, not on differences in stiffness between the corpuscle and the surrounding skin which could be a very important factor and which should be explored in future studies , we chose to give the fibers in our PC model the same properties in as the fibers in the skin.
The isolated Pacinian corpuscle was meshed as a half-ellipsoid, with a major axis of length 1 mm and a minor axis of length 0. The PC model contained hexagonal elements. The indenter displaced nodes vertically, as shown in Fig 3A. A tissue-embedded PC was meshed as an ellipsoid with a major axis of 1 mm and a minor axis of 0.
For the epidermis model, the domain was 1. For the dermis model, the domain was 1. The epidermis and dermis models had and hexahedral elements, respectively.
The long axis of the PC was parallel to the surface of the skin. Nodes on the surface of the skin were indented individually in different simulations to construct the receptive field of the PC.
To observe the effect of PC orientation with respect to the skin surface, a dermally-embedded PC was modeled with its long axis perpendicular to the skin surface. When the PC is mechanically stimulated, a receptor potential is produced and increases until a threshold is reached, and an action potential is initiated [ 4 , 5 , 10 ]. This study used the working model that stretch along the long axis of the receptor, and thus along the nerve fiber at the center of the PC, causes stretch-gated cation channels along the axon to open and initiates the response of the PC [ 30 ].
Length was calculated as the distance between the y-coordinates of two nodes located at the interface of PC and skin elements on the y-axis of the PC. In the case of the vertically-aligned dermally-embedded PC, the linear strain along the long axis Eq 5 was measured with respect to the z-axis.
The multiscale model captured the nonlinear trend in displacement seen in the experimental data and not predicted by an isotropic linear elastic model Fig 4A. As seen in Fig 4B , the multiscale model predicted a nonlinear spacing between nodes, with a greater nodal gap occurring with increasing depth. B To visualize the nonlinearity, lines were drawn to represent the initial first column and final second column of the nodes in the indentation experiment.
The multiscale model third column matched the experimental data much better than the linear elastic model fourth column. In Fig 5 , the isotropic case shows stress of approximately 2x higher magnitude around the indenter than those shown for the circumferentially-aligned case.
The isotropic network case shows higher stress around the indenter than that shown in the aligned network case. As seen in Fig 6 , the strain along the long axis of the axon increased with indentation into the PC. The strain calculated for the isotropic network case was approximately 10x higher than that calculated for the circumferentially-aligned network case.
The cases of circumferentially-aligned red squares network and isotropic blue circles networks are shown. While the long-axis strain increases monotonically with indentation into the PC in both network cases, the isotropic network case showed higher strain than the aligned network case. The long-axis strain along the PC resulting from indentation at various nodes along the surface was also compared for the epidermis and dermis models Fig 7.
The epidermal PC model showed large strain in response to loading directly above the PC that dropped off quickly as the indenter moved away from the PC. This drop-off implies more spatial sensitivity and thus a smaller receptive field.
The dermal PC model shows less indenter position dependence and thus a larger receptive field. The dotted black line indicates the position of a quarter of the PC beneath the surface of the skin. The solid black line on the epidermis plot indicates the contour line for zero strain, which is the strain value below which the neurite would not be expected to respond to indentation. As seen in Fig 8 , the Von Mises strain in the PC in the dermis case shows little variation when the structure is indented at different locations.
In both cases, PC strain is less than that of the immediately surrounding tissue because of its greater degree of anisotropy. The strain in the PC in the epidermis case shows greater variations with indenter location. The green arrows indicate the location of indentation. The large-strain region around the indenter reaches the epidermally-located PC but does not penetrate to the depth of the dermally-located PC. Only one quarter of the embedded PC mesh is shown due to symmetry.
The horizontal PC model showed positive strains or no strain resulting from indentation. The vertical PC model always showed negative strains in response to indentation. This result shows that indentation within the receptive field of a horizontally-aligned PC always results in positive axial stretch of the neurite. Indentation of the vertical model does not result in neurite stretch.
Both models contain a dermally-embedded PC. The scale bars indicate the long-axis strain values for each model. This study used a multiscale finite-element model to determine that the structure of the PC is an important contributor to the nonlinear behavior of the receptor. In addition, it showed that the deep dermal location of the PC provides it with lower spatial sensitivity.
Several factors must be considered when interpreting our results. First, the mechanical stimulus was a fixed indentation into the PC with no transient effects. As such, this study addresses the location and magnitude of the stimulus but it does not take stimulus frequency into account when determining the PC mechanical response, as others have [ 11 ].
A static model was chosen as suitable for comparison with experiment [ 7 ], but it would not be appropriate for simulating the vibrotactile response. While Hubbard [ 31 ] also investigated PC mechanics, the results from the current paper cannot be directly compared to that study, which placed the PC within a hinged apparatus rather than stimulating with a vertical indenter. Second, the PC was treated as incompressible, and no fluid movement was allowed within the PC even though such flow is known to be important [ 11 ]; thus, our model must be interpreted as the instantaneous response of the PC.
Also, the experimental PC literature [ 4 , 5 , 32 ] focuses appropriately on the use of directly applied sinusoidal displacements to elicit the response of the PC to vibratory stimuli, providing a rich data set on the dynamical response of the PC. A model of PC mechanics should include a dynamical component fluid flow, viscoelasticity, or both to account for the phase difference that can occur between skin and PC stimulation, and also between PC stimulation and receptor response.
The mechanical model used in this study also simplified the structure of the PC to account only for anisotropy within the receptor and not for its specific components and detailed structure. The receptor capsule is composed of concentrically-arranged collagenous lamellae through which mechanical forces are transduced.
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.
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