Brain Dissection || Always on My Mind [EDU]

[0:07]Oh worm! Today, we'll be continuing our series on organ dissections and take a look at the anatomy of the brain. The brain is one of the largest and most complex organs in the human body. It is made up of more than 100 billion nerves that communicate in trillions of connections called synapses. The brain controls our thoughts, memory and speech, movement of the arms and legs, and the function of many organs within our body. It's incredible that this large mass of nerve tissue, which is 60% fat, somehow manages to run a complex biomechanical suit and experience consciousness while using less electricity than it takes to work a light bulb. Of course, this is a sheep brain, not a human brain, so there are some differences. The most obvious being size. The human brain is much larger than this, the sheep brain is pretty small compared to us. The first thing we're going to have to do is get rid of this film that covers the brain. This is called the dura mater and it's the outermost layer of the three layers of membrane called the meninges that protect the brain. I'm just going to peel it off with scissors to help.

[1:25]So first, let's take a look at the external anatomy. So this here is the dorsal surface, and when I flip it over, this is the ventral surface. On the ventral surface, you can see the brain stem. The brainstem is located at the base of the brain here and extends down here towards the spinal cord. All information relayed from the brain to the body and vice versa must travel through the brainstem. There are a few different parts of the brainstem. First is the spinal cord here. Then this first bump is the medulla, which controls various autonomic and voluntary functions like digestion and heart rate. The second bump here is the pons, which regulates and controls a number of vital functions such as breathing and sleeping. The next part of the brainstem, the midbrain, is located further in, around here. To see it, I'm going to flip it over and pull back this structure. And now you can see these four bumps here are the midbrain. It's involved in a lot of sensory processing. Now, it's worth noting that a lot of these functions overlap between parts of the brain, and the brain constantly communicates within itself, so these are just generalizations. So these three parts, the pons, medulla and midbrain, make up the brain stem.

[2:47]This structure here is the cerebellum, which plays an important role in motor control. As I lift this brain right now, my cerebellum is coordinating my arm with my brain to make this movement possible. Now when I flip it over, you can see parts of the temporal lobes here, and you can also see parts of the frontal lobe. We'll discuss these more later. These two things here are the two optic nerves which come from the eyes. You can imagine that the eyes are located around here, and the optic nerves bring that information all the way back here, which is where vision actually gets processed. Where these two nerves cross here is called the optic chiasm. These two bumps here are the olfactory bulbs which transmits information about smell from your nose to your brain. It's an extension of the nervous tissue of the brain that extends to the roof of the nasal cavity. Now let's look at the dorsal surface of the brain. So you can see the brain has these many folds, which increase the surface area so that the brain can accommodate more neurons. The raised ridges here are called gyri, and the grooves in between are called the sulci. Now this here is the temporal lobe, which we saw a little of earlier. We just kind of arbitrarily draw a line around here, right here, and say that this is about the end of the temporal lobe. The temporal lobe is involved in a lot of things, but to summarize, it processes memories and integrates them with sensations of taste, sound, sight, and touch. Now, to distinguish the frontal lobe from the parietal lobe, we look for the central sulcus. The central sulcus is right here. The central sulcus runs all the way from the midline here to here, and it separates the frontal lobe from the parietal lobe. The frontal lobe in front is involved in a lot of motor control and also higher order functioning. Higher order functions include consciousness and communication, judgment, learning, etc. The parietal lobe behind the central sulcus, right here, processes sensory information that it receives from the outside world, mainly relating to touch, taste, and temperature. So if I decide to pet a cat, that decision gets made in the frontal lobe here, which then also moves my arm to touch the cat. Then the sensory information, i.e., the cat is soft, gets sent to the parietal lobe here for processing. This region in the back is the occipital lobe, which is involved in processing visual information. So remember the optic nerves we saw earlier? Those lead to the occipital lobe where information from the eyes gets interpreted and processed. Now let's look at the two hemispheres. This longitudinal fissure, right here, divides the brain into the two hemispheres, left and right. The hemispheres are held together by a large band of nerve fibers called the corpus callosum. You can see if I pull it apart here. It connects the left and right sides of the brain, allowing for communication between both hemispheres. Now let's look at the internal anatomy. I'm going to cut through the corpus callosum and separate the two hemispheres. Take a scalpel and cut gently down the center line. Cut through the cerebellum as well.

[6:26]Now let's look at one of the halves. You can see parts of the brainstem again. So medulla, pons, and the midbrain right here. Here is the cerebellum right here. This indentation here is a ventricle. The ventricles are a network of cavities in the brain that are filled with cerebrospinal fluid. They're responsible for the production, transport and removal of cerebrospinal fluid, which bathes the brain. This one here is called the lateral ventricle. It is the largest ventricle in the brain. Here, the circular tissue is the thalamus, which acts as a relay station. When the body registers a sensory impulse, it first travels to the thalamus. The thalamus then passes it on through the cerebral cortex for interpretation as touch, pain or temperature. 98% of sensory information passes through the thalamus, the only exception being information related to smell or olfactory information. This smaller circle to the side here is the pineal gland. The pineal gland regulates circadian rhythm. It produces melatonin which controls sleep cycles. Now this region below the thalamus, right here, is called the hypothalamus, which serves as the link between the nervous and the endocrine systems and is involved in a lot of hormone controls. Now I'm going to cut a cross section of the brain.

[8:00]This is a cross section of half of the brain, just imagine an identical part around here. Now in the cross section, you can see the gyri, which is here, and the sulci here. You can also see that there's a layer of beige area around the edges, and this is the gray matter. The white area in the middle, right here, is called the white matter. Gray matter consists of cell bodies like neuron cell bodies and glia. White matter on the other hand consists of axons. You can see that the corpus callosum here, which we cut through earlier, consists of a band of white matter. This band connects similar areas in one hemisphere to the other. Alright, that's the end of our sheep brain dissection. Thanks for staying, lads. Here's a fun fact about brains to send you on your way. Nearly all colors have a physical wavelength associated with it, but the color magenta doesn't. Rather, your brain is simply processing the color as not green. If you like this video, feel free to like and subscribe for more.