hi everybody and welcome back to miss Angler's biology class I am Miss angler in today's video we are going to be looking at the pelly mechanism of the eye I want you to know that this is an updated version of this video there was an older video that I did create a while back during lockdown for my students but I've decided to redo this video and I've simplified it and made it even easier to remember and learn for exams now if you are new here don't forget to give this video a thumbs up and make sure you're subscribed with your notifications turned on because I post every Tuesday and Thursday and if you are in grade 12 and you're looking for a little extra help you should check out my website miss anger. co.za it is filled with so many free resources as well as some paid for resources like my cheat sheet study guide which is available currently for maths and life sciences and if you are listening to this video in August of 2024 some exciting news is coming soon of two new subjects we are going to be launching very soon in the study guide collection on top of that you can also join my YouTube membership if you'd like a little more one onone live lessons with me so let's dive into the content around the pupillary mechanism now at this point we should know quite a bit about the ey structure but I'm just going to recap what exactly we're working with here so what we've done in this diagram is we have our Iris on the outside here which is the colorful part of our eye and I want you to know that the iris is a muscle itself but it's actually made up of two types of muscle it has an outer radial muscle and Radial means that it's like long and elongated it radiates outwards like that and then it has an inner circular muscle which sits around the p p and as the name suggests it is circular and it is these two muscles that move and change the size of the pupil now why do we have the papillary mechanism we have the papillary mechanism because we want to either change the pupil from small to big or the opposite way around from Big to small because we want to limit or we want to increase the amount of light entering the eye because if too much light enters the eye the image is blindingly bright and it's very difficult to see I'm sure you've had that when you go from a dark room moving into a bright space it's really bright and difficult to see but if you go the opposite way so you go from being in a bright light to a very dark room it takes your eyes a couple of seconds to adjust and get used to the lack of light that adjustment that is happening is one of these two options here and it's the pupil changing size you need to be able to explain how the pubil gets bigger or smaller depending if you are in dim light or bright light so how do you actually go about explaining the Pine mechanism in an exam or a test because you want full marks now this diagram here really is a lovely illustration of what's happening in your eye we start off with a normal light situation and you will notice that the pupil is a medium size and both of the circular and Radial muscles are not at play just yet they're keeping your eye or your your iris at a rest stage if you move into dim light and what is dim light that means Darkness like you're going into a dark room the first thing that's going to happen is the radial muscles which remember those are the muscles that radiate outwards they are going to contract and so if we can't remember where they were remember these are the radial muscles they go outwards the next thing that happens is if the radial muscles are Contracting then the circular muscles they can't contract at the same time so they relax and if we've forgotten where those are remember these are the circular muscles that circle around the pupil the next step is the pupil dilates and what that means is it gets bigger so we're going from a small pupil to a bigger pupil and the final point we want to put here is more light enters the ey and that's how you get four out of four generally this question won't be more than the more than four unless they've married this question with another topic now what happens if you have to explain strong light and what that means is you're going into bright light well you'll notice in the diagrams the pupils have dramatically changed size here one is going from really big and then the other is going really small now you just have to make a very small change you see when you're going into bright light instead of the radial muscles Contracting they actually relax which remember are these radial muscles and the circular muscles on the other hand they now contract you see they do the opposite of what they originally did in our first explanation instead of the pupil dilating the pupil is going to reduce and lastly it's not more light enters it's actually less light enters the eye and so when I tell myrix is very simple if you learn the one explanation like let's say you just learn the dim light explanation this one here the first one we did the strong light or the bright light is just the opposite opposite so the opposite of contract relax the opposite of more less and so you can save time studying by simply learning the one and knowing it's the opposite for the other process it's just important to not confuse your muscles with each other so you need to know who is who and it's important to know what triggers this response is it bright light or is it uh dim light a lovely overlap question for this would come into play when we're doing Reflex because the papillary mechanism is a reflex and a lovely overlap exam question would be if you were asked about reflexes and the papillary mechanism at the same time and they can definitely do this for example they might say something like if a bright torch is Shun in your eyes explain the papillary mechanism and the reflex arc that occurs in the spinal column or the spinal cord to enable this to happen so now you've got two bodies of knowledge you need to work with one the reflex arc and the other the papillary mechanism now as always I like to wrap up these lessons with a very quick terminology recap these are the four main words we need to take away from here number one is the pupil the pupil is that black open hole into your eye and it allows light to enter into your eye so it can go through your lens to your retina in order to change the size of the pupil you are going to use your iris muscle the colorful part of your eye and it is going to contract or relax allowing more or less light in now to do the Contracting and relaxing we have the circular muscles and we have the radial muscles each of these muscles are positioned in a different place in order to facilitate the change in the pupil now now what I like to think of is if the circular muscles the round muscles of the eye are doing the work then we are Contracting them we are therefore making the pupil smaller whereas if we're using the radial muscles which are those long elongated muscles then we are making the pupil bigger and so depending on which one is doing the work will determine if we're making the pupil bigger or smaller if the circular is working we're making the pupil smaller if the radio are doing the work the pupil is getting bigger now if you like this video don't forget to give it a thumbs up and make sure you are subscribed if there's any questions that you have please leave them down below in the comments section and you can also leave future topics that you want me to make videos on that might be missing from the playlist I'll see you all again soon everyone bye