Mechanoreceptors: En- & Unencapsulated

by Thad Wilson, PhD

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    00:00 Mechanoreceptors Mechanoreceptors afferents in the skin. There are quite a few.

    00:08 We will start with pacini corpuscles.

    00:11 This Pacini corpuscles look like more of an onion type of a shape.

    00:16 They are compressible, meaning that you can press them together.

    00:20 They have a gelatinous substance within each of those particular layers.

    00:26 So as you squeeze them down, you’ll get an increase in firing frequency.

    00:31 So you notice that this response to a change in compression.

    00:38 Thus, vibration are sensed very easily through this type of a mechanism.

    00:43 So what vibrations are pretty fast about 40 to 500 hertz.

    00:49 Interesting Pacini corpuscles adapt quite rapidly.

    00:53 And what we mean by that, is they only respond when they are changing the vibration frequency or compressing.

    01:00 After you’ve compressed it once and you’re not still compressing it, they’ve adapt it and they won’t send signal back anymore.

    01:09 They have a really wide receptive field.

    01:12 Meaning that they capture a large skin surface area.

    01:19 If we can trust that with things like Meissner corpuscles, they are located in a different plane.

    01:26 They are usually more vertical versus horizontal in nature.

    01:32 They respond more rapidly to changes in compression.

    01:38 Now, this compression is a little bit different.

    01:41 Instead of being a really a deep pressed or vibration.

    01:45 This is more light touch or kind of fluttering sensations.

    01:51 They also adapt quite rapidly but they have a much narrower receptor field.

    01:56 Meaning that there’s less skin surface area per receptor in comparison to something like the Pacini corpuscle.

    02:04 Ruffini endings? These are ones that are now located in series with the skin.

    02:12 What do I mean by in series? In series means as the skin moves, these will move along with it.

    02:18 And these are great for sensing stretch.

    02:22 And here’s an example of the skin being stretched.

    02:26 You can see that there is a increase in firing frequencies and then a continued firing frequency once the skin is a new stretched position.

    02:37 They are fairly slowly adapting, meaning that overtime they don’t reduce their firing frequency add a new level of stretch and they have a fairly wide receptive field.

    02:48 Meaning that they are not. They have a low density per surface area of skin.

    02:57 Continue it on with some more mechanoreceptor that we have in the skin, there are few that are uncapsulated.

    03:05 These means that they don’t have like a circle around that can be compressed.

    03:10 Good examples of these are things like hair cells.

    03:13 Yes, we have a little sensory nerves around your hairs.

    03:17 And these case as your hair deflexed one way or another, you sensed that as a change in that hair follicle or root plexus.

    03:28 These are free nerve endings that surround the hair follicle.

    03:32 And so, by surrounding it as the hair moves it will enact these particular receptors.

    03:40 In human since we don’t have a lot of hair.

    03:43 These is not something that we talk about quite in the same level.

    03:47 But if you definitely, if you have a four legged companion of some sort whether that a dog or a cat. Their whiskers are definite things that are utilizing these hair cells to a greater degree than we are.

    04:01 We do those still sense base upon hair deflexions and you can do that by lightly rubbing just over the skin and not touching it.

    04:09 But if you do touch your hairs, you can feel it.

    04:14 Merkel’s Cells Merkel cells sense light pressure.

    04:20 These particular ones fire quickly upon light touch and then they are sustained over time.

    04:27 They adapt slowly about will eventually adapt.

    04:31 And they have a very narrow receptive field.

    04:34 and one reason is they are located very superficially in this skin surface itself.

    04:40 Really just below the epidermis.

    04:44 How do we sense mechanoreceptor in the skin? One way to do that is via 2-point touch discrimination test.

    04:52 This is a very simple test but I’ll explain it because it helps us think about receptive field.

    04:58 So you have a calipers that has two distinct points.

    05:03 And you know there’s a two distinct points because you can see the gap between either the protractor or the other device that looks like a wrench.

    05:12 What you do is you place it on the skin and then have the person not look at that area because for example if you look at it, you can see, oh I see a gap Therefore, I’m gonna feel multiple points.

    05:26 But we have to do is not look at it so you close your eyes, you put out your hand or whatever body parts is being tested and they touch it with these two points.

    05:36 If you sense it as two points, you just respond two points.

    05:42 If however, you sense it as one point. even though there were two points, these perception of one point means you are in the same receptive field versus in twos separate receptor fields.

    05:58 This simple test can be done all across the body, and you have different densities of mechanoreceptors in different lowcals.

    06:08 For example, if we tested Meissner’s corpuscles, you can see there’s a close clustering of these in the hand.

    06:16 If we look at Pacinian corpuscles, they have a really wide range or receptive field.

    06:24 And therefore, across most of the hand, you can still only feel one point.

    06:31 This is easily look at across the different areas of the hands, the arm up ways to the shoulder.

    06:38 And you can see as you start to get more proximal to the hand, there’s longer longer spaces in which you can determine to the points.

    06:49 That means that the receptive fields are larger.

    06:52 So places like the shoulder in the upper arm, you can barely tell there are two points for a number of millimeters.

    06:59 If you look at the face like the upper lip, the nose, the cheek, Those are much more sensitive.

    07:05 They have a higher density of mechanoreceptors.

    07:09 And as you go up to the fingers, you can see you have a greater number or a higher density of mechanoreceptors to be able to determine fine types of sensations.

    07:20 so you can grasp and do other potential important items with those lowcals.

    About the Lecture

    The lecture Mechanoreceptors: En- & Unencapsulated by Thad Wilson, PhD is from the course Neurophysiology. It contains the following chapters:

    • Mechanoreceptors
    • 2-Point Touch Discrimination

    Included Quiz Questions

    1. Meissner corpuscles
    2. Pacini corpuscles
    3. Ruffini endings
    4. Merkel disks
    1. Pacinian corpuscle
    2. Ruffini corpuscle
    3. Meissner corpuscle
    4. Merkel corpuscle
    5. Hair follicle receptors
    1. Light pressure
    2. Crude touch
    3. Pain
    4. Temperature
    5. Vibration
    1. Meissner corpuscle
    2. Merkel cells
    3. Ruffini corpuscle
    4. Free nerve endings
    5. Cold receptors
    1. Meissner corpuscle
    2. Pacinian corpuscle
    3. Merkel cells
    4. Ruffini corpuscle
    5. Hair cells

    Author of lecture Mechanoreceptors: En- & Unencapsulated

     Thad Wilson, PhD

    Thad Wilson, PhD

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