Video: Directional terms and body planes

Do you ever feel like you're lost in a maze of human anatomy, trying to decode an anatomical language without a dictionary? If you're like me, figuring cranial from caudal or ventral from dorsal is a very dangerous game, because before you know it, you look more like you're trying to learn the Macarena, rather than trying to learn Anatomy.

Studying human anatomy involves naming and describing thousands of structures and describing their relative position to each other. And unfortunately, saying something is on top of or beside something else just doesn't cut it. Students, clinicians, and anatomists alike rely on a more specific and precise language to describe these relations.

But fear not! Today, we're giving you the ultimate arsenal of terms to navigate this. Say goodbye to the Macarena and hello to confident anatomical orientation.

Let's learn about the directional terms and body planes of anatomy.

When we talk about our bodies in anatomy, we always refer to a standard pose called the anatomical position. It's like the blueprint for describing our body parts regardless of how the body is positioned in real life. In the anatomical position, we always consider the person as standing upright, looking forward, with arms to the side, palms facing forward, and thumbs pointing away from the body. The feet are slightly apart and parallel to each other with the toes pointing forward.

Let's get straight to the directional terms that help us in describing the location of body parts or structures.

The first pair of terms that you need to know is anterior and posterior. Anterior indicates that the body part in question is in front of or front. Posterior indicates that it is behind of or behind. For example, your toes are anterior to your heels and your heel is posterior to your toes.

The next pair of terms are ventral and dorsal. Ventral indicates something is towards the front of the body and dorsal means towards the back of the body. Ventral comes from the Latin word 'venter', which means belly. So, ventral literally means towards the belly which is towards the front of the body. Dorsal comes from the Latin word 'dorsum', which means back. So, for example, the kneecap is located on the ventral side of the knee joint while the popliteal fossa is located on the dorsal aspect.

Our next directional terms are right and left, which, lucky for us, is quite straightforward… well, kind of. Just remember that when thinking about left and right, you always have to think of it in the anatomical position, not the position of something when you're looking at it on a screen or in a book. So this is the right lower limb and this is the left lower limb.

Next in our arsenal of terms are proximal and distal. Distal means that it is away, or distant, from the trunk or the point of origin of a certain structure. Proximal means that it is closer, or in proximity, to the trunk or point of origin. So we can say that the elbow joint is proximal to the wrist joint and the fingers are distal to it.

Now if we split the body in half this way to equal left and right parts, the line down the middle of the body is called the median or midline. This is key in understanding the directional terms – medial and lateral. Medial means towards the median or towards the midline of the body. Then lateral means away from the median. So we can say that your nose is medial to your eyes because it's closer to the midline while your ears are lateral to them.

Superior means above or upwards. And of course, if there's an up, we must also have a down, and the term we're looking for in in this case is inferior. Inferior indicates below or downwards. So, for example, the nose is superior to the mouth while the chin is inferior to it.

You'll also sometimes see the terms cranial and caudal instead of superior and inferior. They literally mean towards the cranium, or head, and towards the tail, or coccyx, respectively.

You may often also see the term superior converted into the prefix supra- as in the supraclavicular lymph nodes, which are located superior to the clavicle, and you may also see inferior as the prefixes such as infra-. For example, the infraorbital artery is located inferior to the orbit.

Two other prefixes similar to infra- are hypo- or sub-, both of which mean under. The hypoglossal nerve is inferior to or under the tongue and the submandibular lymph nodes are located beneath the mandible.

Two additional pairs of terms which we need to look at now are superficial and deep, as well as external and internal. These are kind of related to each other, however, are not completely interchangeable. Superficial and deep refer to position relative to the surface of something, usually the skin, for example; for example, the superficial gluteal muscles and the deep gluteal muscles. External and internal, sometimes also called outer and inner, describe whether something is located on the outside or inside of something. For example, the stomach has an external surface and an internal surface.

Now that we've learned about the major directional terms, it's important to note that using one-directional term is often not enough to describe the location of a structure in relation to another. Fortunately, we can combine them to give a more accurate description of anatomical structures.

The liver is located below the heart and away from the midline, so we can describe that as inferolateral. To combine the two directional terms, we usually abbreviate the first term like in this list, and then add it to the second term.

Now let's take a few moments to discuss some regional directional terms, which is specific to certain parts of the body.

Let's begin with the brain. Now we came across some of these terms earlier on, but in the brain they have different meanings which can be confusing. In the cerebrum, we sometimes use the term rostral instead of anterior. Rostrum comes from the Latin word for nose, or beak, so think of this term as anything pointing anterior towards the nose. The term caudal in the brain means the opposite of rostral and can be used instead of posterior when describing structures of the cerebrum. When describing the inferior aspect of the cerebrum, we use the term ventral while the superior aspect is referred to as the dorsal aspect.

Moving down to the brainstem, we can see here the anterior, posterior, superior, and inferior directions to orientate ourselves. As with the rest of the body, the anterior and posterior aspects of the brainstem may also be referred to as the ventral and dorsal aspects, respectively, while the superior and inferior aspects can be called cranial and caudal.

Moving further down to the hand, the anterior aspect is often referred to as the palmar or volar aspect of the hand while the posterior aspect or back of the hand is referred to as the dorsal aspect. The thumb is on the lateral or radial aspect of the hand while the little finger is on the medial or ulnar aspect.

We're going to move on now to the feet. The underside, or sole of your foot, is known as the plantar aspect of the foot. To help remember this term, think of your feet as being firmly planted on the ground. On the opposite side, we have the dorsum of the foot which is the area facing upwards while standing. This can be a little confusing because as we've already seen, dorsal typically means towards the back. You can blame embryology for this one.

Now to further help us navigate the human body, we also have anatomical planes and axes that serve as reference points for anatomical descriptions and movements.

Body planes are imaginary planes that slice or section the body in its anatomical position. Try not to get too spooked out here but if we were to slice the body vertically, we would get an anterior part and a posterior part. This is called the coronal or frontal plane. Now the word coronal is derived from the Latin word 'corona' which means relating to a crown or coronation. So imagine a king or queen who wears a crown that is slightly too sharp and splits their body into two.

Then we have the sagittal plane. It is also a vertical plane but it splits the body into left and right parts. A sagittal plane that runs directly through the midline is also called the midsagittal plane or median plane.

Next we have the transverse plane, which is a horizontal plane that divides the body into superior and inferior portions. We also sometimes refer to this as a cross-section.

In addition to anatomical planes, we also have anatomical axes. These are straight imaginary lines that run through the body along three directions. We have the horizontal axis, also known as the mediolateral or x-axis, which passes from left to right and is formed by the intersection of the coronal and transverse planes. The vertical axis, also known as the longitudinal or y-axis, and this axis passes inferior to superior and is formed by the intersection of the sagittal and coronal planes. And the sagittal axis, known as the anteroposterior or z-axis, passes from anterior to posterior and is formed by the intersection of the sagittal and transverse planes. These axes are usually used to describe a line around which a body part rotates, typically the movement around a joint. For example, the elbow joint sees the movements of flexion and extension occurring around a horizontal axis in the sagittal plane.

And that's it! Today we managed to take a quick look at the arsenal of terms we need to orientate ourselves and navigate the human body. Farewell, Macarena! Hello, mastery of anatomical orientation!

See you next time!