 Okay. Sorry about that. Okay, so we're going to talk about the light pathway today. And so in talking about the light pathway, we first have to kind of talk about how light travels in the eye. So obviously light comes in and it first hits the tear layer. I didn't show that here. But after hitting the tear layer, it then hits the cornea. The cornea goes through the iris. After the iris, it goes through the lens and then it goes to a focal point onto the retina. From there, it travels to the optic nerve via retinal ganglion cell axons, which makes up the optic nerve. And then, of course, to the brain. And so in terms of the retinal anatomy, there's obviously a hierarchy to the structure of the retinal cells with light first entering in through the bottom and then traveling towards the backside where the photoreceptors are located. And so how does an image, how does an image produce? So what happens is as light is reflected from an image where you see number one, it gets sent through into the eye via the pathway that I just explained, it's actually inverted. So the actual organ, the eye itself sees an inverted image. It then gets trans, that image gets transported over to the optic or occipital lobe where it then gets processed into the actual image that we perceive. And so, of course, that is shown as an A in our occipital cortex. And so when talking about the light pathway, it's important to talk about how light is transduced. And so what happens is you have this opsin protein, which is important as a component to the actual chromophore. And specifically in rods, it's located at the cell disc membrane. Consists about 348 amino acids. And again, it complexes with the chromophore. In this case, it's retinaled in order to form a rhodopsin. And so the chromophore itself, obviously absorbs light, has a specific wavelength, and it gets transformed from this 11 cis to the 11 trans after being excited by light. And then, of course, the trans-retinal form is what's considered to be energetically unfavorable in this opsin molecule. So in terms of the reactionary intermediates, so the goal for the retinal is to expel the used up chromophore and then have it be recycled via the pathway that I'll explain in a few seconds. And so what you have are these multiple intermediates. You go from rhodopsin to beta-rhodopsin to lumi-rhodopsin to metero-rhodopsin 1, and then finally, rhodopsin 2. And metero-rhodopsin 2 is the form that actually gets transported and actually is involved in a light transduction pathway. And so the trans-retinal form is what is actually released and then sent to the RPE, and then from the RPE is recycled into the 11 cis form. So hyperpolarization is actually what is used to conduct the signaling from light capture and then forming it into a chemo-electrical signal. So what happens is you have this closure of these sodium channels which leads to this hyperpolarization of the cell. And then, of course, the potential difference travels from the rods to the bipolar cells and then finally to the retinal ganglion cells. So, like I said, metero-rhodopsin 2 is the form that's actually involved in the transduction pathway. So what happens is metero-rhodopsin complexes with transducin, and then this activates the enzyme photodiesterase. And as you can see here, the metero-rhodopsin binds to the transducin which then is complexed and then activates that photodiesterase molecule. So color vision, how is it different from monochromatic vision? It has the same principles, however, the only difference is in the actual opsin molecule itself. Each cone has a specific spectra of absorption for light, and so that's why you have the different colors, or at least the three different colors that we know that are specific to cones. And, of course, this is the rod signal transduction pathway that I explained before. And so, like I was explaining, there's the metero-rhodopsin that binds to, or there's the opsin plus the retinal, which forms the cis retinal, and then light enters, and then it transforms that into a trans retinal form. The metero-rhodopsin 2 then binds to the G protein receptor transducin. Then that forms in a complex with the photodiesterase unit. And then from there, cyclic GMP is converted to GMP. And then that later then closes the ion channel, the sodium ion channel here. And so less CGMP leases closure. And so when you have less closure, you have this hyperpolarization, and so less glutamate is being produced as a result. So what happens from between dark and light? So what you have is this release of glutamate in the dark, and that's constantly being generated. And so you have this sodium channel that's being closed. And so when you do have light, when you are in a light environment, what that does is it stops to release of glutamate that then leads to the opening of the sodium channel, and that leads to further that hyperpolarization. And so when you talk about the pathway vision, I just explained the photoreceptors and light signal, it then goes, it travels through the optic nerve, eventually getting into the optic chiasm, the optic track, and then goes on to sub nuclei in the brain. And so you have lateral geniculate nucleus, you have a superior colliculus, and then the pineal gland. And then later goes through the optic radiations, finally reaching the optic low, which is the primary visual cortex center. And so in talking about the different paths, just quickly going through the chiasm, this is where the retinal output from the retina first kind of it desiccates into into several fibers. The most important thing to remember here is that there's a about 51 to 53% of the retinal fibers are desiccating as they reach the optic chiasm. And so if you have, say, an injury beyond that we call retrochiasmal injuries, it's possible to affect, say, the pupillary fibers, especially when we're talking about, say, an RAPD. So you can get an RAPD as a result of a retrochiasmal injury. And so this is kind of further elucidating the conversion points for the retinal or the the signal coming from the retina. As I said, you go through the chiasm and then of course, the lateral geniculate body. But prior to that, you have connections that go to the hypothalamus to the pre tectum, as well as the superior colliculus from the from the fibers that are desiccating. And then, of course, the optic radiations and finally the striate new cortex. And just to kind of continue on this description of the different pathways, of course, again, the optic track. And this just then projects to the lateral geniculate nucleus, as well as the superior colliculus. I will talk a little bit about the different sub nuclei. So you have the lateral geniculate nucleus, and its primary function is it receives the main, the main support or the main amount, or the majority of the relay signals, or is the relay pathway for the signals from the RGC. And then, of course, the superior colliculus. This is important for head as well as eye orientation and movement. The pineal gland is another area where fibers are sent to. This is important for the production of melatonin, which is considered the hormone involved with circadian rhythms. And then you have the occipital lobe, which is the primary visual cortex. And again, this is the final step for this relay pathway from the RGC through the multiple paths. That is the light pathway.