Alright Ninja Nerds! What we're going to do in this video is, we're going to talk about the pineal gland. Alright, so the pineal gland is really cool a little gland. It's located in what's called the diencephalon. So what's the diencephalon? A little bit nothing crazy, a little bit into a neuro anatomy here. The diencephalon is actually consisting of a couple different structures, it consists of the thalamus, the hypothalamus, and what's called the epithalamus, which consists of the pineal gland and that's also called the habenula or habenular commissure. But it's kind of deep to what's called, this your cerebrum right here, all of this is your cerebrum, it's deep to the cerebral cortex which a bunch of grey matter inside deep to the cerebral cortex. Okay, now here I'm zooming in on the pineal gland. Okay, so this right here is our pineal gland. So again this right here is the pineal gland, just to kind of give us anatomical position here, this is the thalamus and this right here is a nuclei present within the hypothalamus and extremely important nucleus, extremely important. It's called the suprachiasmatic nucleus. This is your midbrain, pons, medulla and then the part of the spinal cord down here and cerebellum. This is an important ganglion we're not going to talk too much about it, I'm just going to mention it we'll get to it in a second though and this is the optic nerve and then this is going to be the eyeball right with on the back part of it, the important part which consists of all the photoreceptors like the rods and the cones, this is going to be the retina right there. Here's the eyeball, this green structure is going to be the retina and then we have a lot of these ganglion cells that are actually bringing this information to the suprachiasmatic nucleus. Alright. Pineal gland, what is it function? It's function is to be able to regulate our sleep and wake cycles, our diurnal cycles. Alright and it also plays other roles that we by discussing a tiny bit of detail. Alright, so here we go. Did you know the also call the pineal gland the third eye? Why? So you know that the retina of the eye has a direct connection to the pineal gland or kind of indirectly, we can actually say. Let's say here we actually have in red, let's show this as specifically light. So this is denoted to say light. And then we will have over here in black we'll describe this as darkness. Right, so darkness okay. Whenever there's light, what it does is it stimulates the action potentials down this axon right? And then triggers different types of reactions in the suprachiasmatic nucleus, which sends signals down to this structure and then up to the pineal gland. Let's take a look at what's happening then. So let's say that we actually have light, light is going to stimulate these action potentials, so let's draw that in red. Here it's going to stimulate, let's draw, stimulate these action potentials down this actual axon here and then it's going to release specific type of chemicals onto the suprachiasmatic nucleus that of glutamate usually. And what it's going to do is, it's going to trigger different types of mechanisms inside of the suprachiasmatic nucleus. Now, the suprachiasmatic nucleus is also referred to as our biological clock. So he can regulate a bunch of different activities within our body, to regulate our biological clock, our sleeping or waking, you know different things like that. Right so, what happens is he's going to get this stimulus right and what he's going to do is, he's going to secrete different chemicals which can affect multiple different nuclei. We're going to briefly talk about these they're not important, but the paraventricular nucleus, will get stimulus here, he'll come out here, down to your lateral grey column, come out here to what's called your superior cervical ganglion. And then what happens is your superior cervical ganglion, this is where it's important. The superior cervical ganglion has direct connections to the pineal gland. So now I'm going to show this in blue here, watch what happens here. This guy's going to release specific type of chemicals, so what do we say here. What was the most important thing? Light stimulates these action potentials, stimulates the suprachiasmatic nucleus to do different types of changes within our biological rhythm, which stimulates the paraventricular nucleus. The paraventricular nucleus does what? He sends these signals down, right? He'll send these signals all the way down through the lateral grey column of our spinal cord. And from the lateral gray column of our spinal cord, the axons will go out to the superior cervical ganglion. And then from the superior cervical ganglion, these post ganglionic motor neurons will come directly to the pineal gland. Now, what happens here? This superior cervical ganglion is going to secrete some really important chemicals. And this important chemical is called neroepinephrine. Okay that's interesting, right? On the actual pineal gland, are these pinealocytes. Because the pineal gland is made up of pinealocytes. It has receptors for the norepinephrine. What the norepinephrine does, is it binds on to this adrenergic receptor right here. So it binds on to this adrenergic receptor. What does it do? It triggers a bunch of mechanisms inside of this pineal gland. What is the overall purpose? What it does is, you know there's what's called tryptophan? So you have tryptophan here, and then tryptophan can eventually get converted into what's called another molecule which we call 5-hydroxytryptamine. And then 5-hydroxytryptamine can get converted into what's called serotonin. And then serotonin can eventually get converted into what's called melatonin. What is norepinephrine doing? It's stimulating these intracellular pathways to stimulate this conversion here, to stimulate this conversion here, to stimulate this conversion here and what's the overall process then? We're stimulating the synthesis of melatonin. Now here's where we need to get something extremely straight here. When this is occurring in light, this mechanism isn't completely known to the detailed point. But when it's in light this pathway that we just talked about here right? So coming from the superior cervical ganglion here, let's follows up these impulses coming from the superior cervical ganglion and releasing norepinephrine pineal gland they're lower, so this release here is lower during light. Okay, then in darkness, what happens? DARKNESS everybody, darkness. It inhibits this actual impulses right guys, from going to the suprachiasmatic nucleus. So then it changes different types of rhythms and different types of biological processes that are occurring in the suprachiasmatic nucleus, right? That then sends signals to the paraventricular nucleus, to the superior cervical ganglion. And from the superior cervical ganglion, it goes to the pineal gland. What's the difference here? When it releases the norepinephrine, so it's lower during the night, guess what? You make higher norepinephrine during darkness. Now here's what's important, you have to regulate a balance because obviously if you don't make enough of what? If you don't make enough of this norepinephrine, you're not going to make enough melatonin. And if you make too much of this this can cause problems too right, because you have to find a happy balance, a happy medium with this norepinephrine right? And that's the whole purpose here. That's what this superc asthmatic nucleus is doing. What is this melatonin go and do? Because whenever this is stimulating this pathway is actually going to be this light pathway going to suprachiasmatic nucleus, paraventricular nucleus, lateral grey column, superior cervical ganglion to the pineal gland. When it's occurring in light, watch this I'm going to show this in red. There's very little melatonin. So very, very little melatonin being secreted during the daytime right, during the light. But when it's in this darkness, all right and it goes to suprachiasmatic nucleus, the suprachiasmatic nucleus receives these signals, sends it down through the paraventricular nucleus to the superior cervical ganglion, to the pineal gland. and it releases more norepinephrine and then therefore releases more melatonin. So in darkness, look what happens to the melatonin levels. You have higher melatonin levels. When there's higher melatonin levels, what does it do to the suprachiasmatic nucleus? It acts through different types of receptors and stimulates the suprachiasmatic nucleus to reset the biological clock. So what is it going to do, it's going to reset the biological clock. So in summation, what can we say is the function of the pineal gland? We can say the function of the pineal gland is to do what? To secrete melatonin. And what does that melatonin do? It regulates our sleep and wake cycle via the..? So it regulates what's called our diurnal cycle, our sleep and wake cycle via who, the suprachiasmatic nucleus, which is located in the hypothalamus. That's the whole purpose here and what's stimulating this process of the pineal gland to make melatonin. This is stimulated by darkness. So darkness is one of the primary stimuli of the pineal gland right, via all these actual other signals right? But again biggest overall concept, overall concept together is that darkness works through different mechanisms to stimulate the pineal gland to release melatonin. And that melatonin regulates your sleep and wake cycles by acting on the suprachiasmatic nucleus and what is the suprachiasmatic nucleus do? It resets our biological clock through various complex mechanisms to help induce the actual drowsiness and trying to get you're getting sleepy right to be able to induce the sleeping process, right? So that's the purpose of the pineal gland. Whereas in light, it inhibits the pineal gland it releases.. So again in light, what does it do? It inhibits the pineal gland releases less melatonin, less melatonin is actually not going, it's going to affect the regulation of the diurnal cycle via the suprachiasmatic nucleus by how? It's going to make you awake. So with this you would actually be awake, versus with the darkness you would actually have sleep, your sleepiness. Right so sleepiness. So this is how it does that. The pineal gland has indirect input from the actual visual pathway and from that input it can help to regulate our actual sleep and wake cycles via activating or inhibiting the suprachiasmatic nucleus, who will then control that by controlling our wakefulness or our sleep fullness. Alright, Ninja Nerds, I hope this made sense alright. Take it easy Ninja Nerds!
