So now that we've learned all about anatomical position, we're going to learn a whole bunch of directional terms, and these directional terms are going to help us communicate where things are in the body, specifically where things are relative to each other. Before we do that, though, we want to talk about the basic human body plan because some of these terms are going to be dependent on how the body is built. So, the first thing to know is that humans are considered to have bilateral symmetry. Now, bilateral symmetry just means that the two sides of your body are symmetrical.
And as we look at this image over here, we can draw a dotted line down the middle of the body, and you can see the left side and the right side are mirror images. You have a right arm, you have a left arm, you have a right ear, you have a left ear, etc. Importantly, not everything in your body is a perfect mirror image. Your internal organs definitely are not a perfect mirror image. They're not a mirror image at all.
But for the most part, when you look at somebody’s left and right, they mirror each other. Now bodies also consist of a trunk and limbs, and we've highlighted the trunk here in orange and the limbs in blue. So the head and trunk, we're going to refer to as the axial portion of the body, while the limbs, we're going to refer to as the appendicular portion. Now, for this unit, you probably do not need to know 'axial' and 'appendicular'.
You don't need to know those words. You will need to know those words later on in this course, specifically in the skeletal unit, so it's not the worst thing to learn them now. However, the idea that you have a core—your head, your thorax, your abdomen—that that's one part of your body, and that you have limbs that operate quite differently as a different part of your body, that's going to be important to keep in mind as we learn some of these directional terms. Now as we go through these directional terms, it's important to remember that they compare relative locations. Alright?
When you say something's to the left, that does not mean it's all the way to the left. Something's to the left compared to something else. Something is up; it's not up all the way up. It's up compared to something else.
These terms are relative. And for that reason, they generally come in pairs. Right? If there's an 'up,' there's a 'down.' If there's a 'left,' there's a 'right.'
If there's a front, there's a back, etcetera, etcetera, etcetera. And lastly, the thing to really remember when you're learning these terms is that it always refers to a body as if it's in the anatomical position. So it doesn't matter what position the body is in. It might be a contortionist in the craziest handstand you have ever seen. When you talk about directional terms on the body, you are assuming that the body is standing just like this.
Alright, with that, let's go learn some directional terms.
