so we are going to do a video of sheep brain dissection today. On my hand you see a sheep brain, really small in size and that's one of the differences between sheep brain and human brain. The human brain is much larger, the human brain is also more rounded. The sheep brain is kind of elongated and also because the sheep are four-legged animals so you see the posterior part of the she brain is is kind of elongated and it's more posterior (horzontal) while in human beings this area- the brain stem and the cerebellum would have been more inferior. Because human beings, we are bipedal so the spine goes down like this. Now let us first try to see the major structures without you know cutting the brain. The brain has four main regions- the cerebrum, the cerebellum, the brain stem, and the diencephalon, which is the central core of the brain that you cannot see without cutting open the brain. So we'll start with the cerebrum. The superior view of the brain gives shows you the cerebrum here and on the surface of the cerebrum you see ridges which are the the 'ups' the elevations and the grooves, the shallow grooves. So the ridges are called the gyri and the shallow grooves are called the sulci. You can see the ridges and the grooves. The deep grooves are called fissures. So you see a longitudinal fissure here that is separating the cerebrum into the left and right cerebral hemisphere. There is also the central sulcus that is separating the frontal lobe from the parietal lobe, not very distinct but you can kind of see this. So the cerebrum is divided into lobes you can see here the left and the right frontal lobe; the left and the right parietal lobe; the left and the right occipital lobe; and the left and the right temporal lobe. So these are the lobes of the cerebrum. Behind the cerebrum, this small region of the brain, this is called cerebellum or the small brain and the cerebellum just like the cerebrum has also left and right parts. The left and right hemispheres of the cerebellum are connected by worm like structures. This is called the vermis. Behind the cerebellum this is the brain stem. The brain stem has three parts. If you look at the inferior view of the brain this is the spinal cord. Then as you're going up or anteriorly from the spinal cord the first bump that you feel this is the medulla oblongata. This is the inferior most part of the brainstem. Then the next bump here- this is called the pons. This is the second part or the middle part of the brainstem and then finally you see here- this is the superior most part of the brainstem this is mesencephalon. Specifically these are the cerebral peduncles of the mesencephalon. These are two fiber tracts, okay, relaying messages taking messages to the cerebrum. Now if you see the superior view of the brain, if I separate the cerebellum a little bit from the cerebrum you can see another part of the mesencephalon. There are two big bumps or bulges here, two big protrusions called the two superior colliculi and also two small protrusions here. These are the two inferior colliculi and all four of these together are called the corpora quadrigemina. So this is from the superior view what you can see of the mesencephalon and in the inferior view you saw the cerebral blood peduncles. You also see, as you are go moving anteriorly this structure here this is a remnant of the optic chiasm. The optic chiasm is this cross shaped structure. So imagine two optic nerves- nerves coming from your eyes and they make a cross shape structure and they go here then they are known as optic tracks. So this is a remnant it got cut when the dura , the covering of the brain was getting removed. Right behind this optic chiasm you see this space where I can put my probe in this is where the infundibulum, that means the stalk of the pituitary gland, would have been. It also got cut so if the pituitary was still intact it would be hanging from the brain like this. Right? So this is the place where the infundibulum comes out. As we go more anterior these are the olfactory bulbs. So your remember olfaction is your sense of smell. This is also a feature that is different in sheep. Between sheep and humans- sheep have bigger olfactory bulbs because their sense of smell is more developed than human beings. These are all the structures that you can see in the sheep brain inferior view without dissecting it. We've already covered the structures from the superior view. Now for the dissection. What you do is a mid sagittal section. You should put the brain specimen down on the tray and then with a scalpel and the blade you start going like this. Go slow as you're gently cutting this you know the mid sagittal section. You cut and you tease. You cut and you tease and as you tease you will see there's no real actual physical connection between the two cerebral hemispheres but at a certain point you will see kind of a floor and you will see a carpet of white fibers. That's the biggest white matter bundle in the brain. It's's called the corpus callosum and we will see that when we do the dissection also. So you do a midsagittal section like this then you turn the brain and then you again cut from here. And there's a line guiding you how to do the mid sagittal section. There is a line naturally there so you cut like this once you have cut the brain and you have obtained two halves of the brain left and right. It would look like this, okay? So this is already dissected out. So let's try to see the structures that we have you know we can see as you were cutting. These are the sulci you know of the cerebral hemisphere. This layer here, this one. This layer is the corpus callosum, the bundle of white matter that was that is the only connection between the left and the right cerebral hemispheres. It helps in communication between the two hemispheres. Now this corpus collosum, you see, it makes a loop like structure so it goes here also. And this part is called fornix and this corpus callosum and the fornix they are enclosing a space inside that is hidden by a thin membrane. You see this thin membrane this is known as septum pellucidum and I can tear through this membrane and expose the space inside. This space is the lateral ventricle. So if you think of the lateral ventricle as a room, then the ceiling of the lateral ventricle is the corpus callosum, the floor is the fornix and there were two lateral ventricles- remember the ram's horns? So one is in the left cerebral hemisphere. The second one is in the right cerebral hemisphere. And they would be separated by a curtain and that curtain is septum pellucidum. Now under the fornix you see this round kind of circular or egg-shaped structure. This is thalamus. Thalamus is part of your diencephalon. Diencephalon has three parts- thalamus, epithalamus, and hypothalamus. So above the thalamus is a thin layer of Epithalamus and this epithalamus houses an important endocrine gland- the pineal gland. The pineal gland makes the hormone melatonin that regulates your sleep-awake cycles. So this is epithalamus, pineal gland. Below the thalamus, this region here is hypothalamus. Hypothalamus is an important autonomic nervous center. This structure, remember, this is part of the optic chiasm. When the brain was intact this is the optic chiasm. So this part is optic chiasm and this structure that you see here this is mammillary body. This is associated with memory and sense of direction and the area between the optic chiasm and the mammillary body, this area is hypothalamus. That means if the brain was intact and the pituitary gland was still there it would be hanging like this. And when I open it this is where the hypothalamus would be. The hypothalamus is the boss's boss. It regulates the pituitary gland, which is the master endocrine gland. Now this epithalamus, it also surrounds the third ventricle, which is another cavity in the brain that contains cerebrospinal fluid. The lateral ventricles also contain cerebrospinal fluid (CSF) and this one also contains cerebrospinal fluid. There would be special blood vessels, you see this this is a choroid plexus which makes the CSF. You see this dark pigmented area. So the third ventricle is around the thalamus. It goes like this here and then it continues. This is the cerebral aqueduct. Also called the aqueduct of Sylvius. This is the connection between the third ventricle and the fourth ventricle. This is the fourth ventricle. So then the cerebro spinal fluid would come go into the fourth ventricle and then it goes down into the central canal of the spinal cord. This region here is the cerebellum, okay, the small brain and you can see the dark and light areas- the dark areas are the gray matter and the white area is the white matter of the cerebellum. This white matter is called The Tree of Life because of its resemblance to the small tree, it's calledarbor vitae. So we have covered some of the major internal structures. We did corpus callosum, lateral ventricles, septum pellucidum, fornix, thalamus, epithalamus, pineal gland, optic chiasm, hypothalamus, mammillary body, third ventricle, cerebral aqueduct, fourth ventricle, then the central canal. We covered cerebellum, arbor vitae, and the gray matter. I think we are done. if you like this video please don't forget to hit the subscribe button.