Muscle tissue is unique to animals and is capable of contraction. That's how animal locomotion works. There are actually 3 types of muscle tissue that we'll talk about. These are skeletal muscle, which is attached to bone and used for locomotion and posture. And you can see right here, we have some skeletal muscle. Then, we also have cardiac muscle, which you can see right here. This is cardiac muscle only found in the heart and its job is to contract the heart and help the heart pump blood. And it's got some super interesting features that relate to signal transduction in the nervous system sense. Well, I'm getting ahead of myself because I'm excited, but we'll get to all that in a later lesson. Lastly, we have smooth muscle. This is found in the walls of organs and vasculature and is what allows them to contract. And you can see some smooth muscle, right behind my head here. Boom, smooth muscle.

Now, the last type of tissue that we'll talk about is epithelial tissue. This lines organs and body surfaces and its main job, the thing that makes it so important, is it can separate interior and exterior environments. This allows organisms to create unique environments which allow for some drastically different chemical and physical conditions. This is super important. I mean, think about it. Your stomach is full of acid, right? You need that for digestion. But, obviously, if that stuff leaked out into your body, you would be done for. Thankfully, we have epithelium that will line our stomach and keep those environments separate. You can see an example of epithelial tissue right here. This darkened line that crosses through them is meant to represent the barrier that they create between the two environments. And there's a little bit of terminology that you should know. The apical side of the epithelium faces away toward the exterior environment. So here, we have our apical side. The basal side faces the interior of the animal or the organ, for example. And lastly, there's a special type of extracellular matrix on the basal side that epithelium sits on. This is called the basal lamina, and you can see a nice image of it here. We are looking at a small portion of the exterior or the sort of outer edge of a cell here. This is the inside of the cell. This is the outside of the cell. And this dark line right here is that basal lamina that the epithelium will sit on. That's all I have for this lesson. I'll see you guys next time.