Anatomical terminology

Transcript

Content Reviewers:

Antonella Melani, MD

When someone talks to us, we’re only able to understand them if we know their language. Well… the same thing goes for anatomy!

To study anatomy and communicate among peers, we have to use specialized terminology that helps us describe the structures of the human body, where exactly they’re located, and their relationship to one another.

If I tell you to look at the right-most finger of your hand - which one will it be? Your pinkie? Your thumb? It will depend on the position of your hand and whether you're looking at the back or the palm.

This is why all anatomical descriptions are expressed in relation to one consistent position to eliminate any ambiguity.

Anatomical position, is the position that is globally adopted for anatomical and medical descriptions of the human body. Now, let’s describe the position the body is in when we refer to anatomical position.

When a person is in the anatomical position, they are standing straight up with their legs close together, their feet parallel to one another, toes directed forward, their arms are down at their sides with the palms of their hands facing forward, and they are keeping their head up and gazing straight forward. All descriptions of the body refer to the position shown here.

Now, if we’re looking at someone in anatomical position, there are four imaginary planes that intersect the body to help us with anatomical descriptions.

First we have the median plane, which is an imaginary vertical plane going through the body’s midline, over structures such as the nose and belly button, separating the body into right and left halves.

Second, are sagittal planes, which are also vertical planes, but aren't fixed, meaning that they could be placed anywhere parallel to the median plane, dividing the body into uneven left and right parts.

You might also hear the term paramedian plane, which describes a sagittal plane that is near the median plane. Next we have frontal planes, also known as coronal planes.

These imaginary planes are also vertical, but perpendicular to the sagittal and median planes, meaning they go from left to right, separating the body into a front portion and a back portion.

Finally we have transverse planes, which are the only horizontal planes, and thus are also known as - you’ve guessed it! - horizontal planes.

These planes are perpendicular to the median and sagittal planes as well, but they divide the body into an upper portion, and a lower portion.

In radiology, it’s also common to use the term axial plane, which is short for transaxial plane. The use of planes allow us to cut the body into sections, which provide a view of depth.

Longitudinal sections refer to sections that are cut along the longitudinal axis of a structure. Transverse sections, also known as cross sections, are perpendicular to the longitudinal axis.

These sections are useful for understanding the relative depths of different internal structures and their position in relation to each other.

Last but not least, oblique sections are sort of intermediate to the two sections we’ve talked about, since they’re not cut in a straight, defined plane, but rather in diagonal.

Now, here are some examples of anatomical structures being shown in different planes and sections. Pause the video and see if you can correctly define the plane of view!

Alright! Now, when an anatomical structure is introduced, it is common to describe its position or location related to surrounding structures, and this is done with specific anatomical terms.

Among the most frequently used terms, we have up and down directions, which are termed superior and inferior. Let’s go back to the anatomical position!

Okay, so superior means towards the head, while inferior means towards the feet. So we can say that the chest is superior to the hip, but inferior to the neck.

Another way of saying this is using the terms cranial and caudal. Cranial refers to the cranium, or head, while caudal refers to the cauda, which means tail in Latin. So, caudal means towards the tail or feet.

In the human body, the cauda can either refer to the coccyx, which is the most inferior bone in the vertebral column, or simply to the feet.

Keep in mind that the terms cranial and caudal are commonly used to describe embryological structures and their growth or development.

Now, to indicate that a structure is in front of another, we use the terms anterior, as well as ventral, which literally means ‘belly’ in Latin.

When referring to structures in the head or brain, we can also use the term rostral, which means nose or beak. For example, the nose is considered a rostral structure, and the frontal lobe of the brain is rostral to the cerebellum.

On the other hand, to indicate a structure that is more towards the back, we can say it is posterior, or dorsal, which means ‘back’ in Latin.

However, keep in mind that the term dorsum or dorsal surface can also be used to describe the superior part of a structure that projects out of the body anteriorly, like the nose or foot, as well as the posterior surface of the hand.

On the other ...hand, the anterior surface of the hand is known as the palmar surface. The sole is the inferior aspect of the foot which is referred to as the plantar surface.

This may seem confusing, but if we think of a bear walking with its four paws touching the ground. The palmar and plantar surfaces are what would be touching the ground and the dorsal surfaces are the upper sides of the hands or feet that are not touching the ground.

Now, to describe a structure’s relative proximity to the median plane, we use the terms medial and lateral. Medial refers to a structure that is closer to the midline or median plane, while lateral refers to a structure that is farther from it.

So, when looking at the head, our eyes are closer to the midline than our ears. Therefore, we could express this by saying that our eyes are medial to our ears, and our ears are lateral to our eyes.

Next, there’s external and internal, which refer to the proximity to the center of an organ or cavity, regardless of the direction. External indicates structures that are outside or further from the center, while internal means inside, or closer to the center.

So, for example, our heart, which is in our chest cavity, is more internal, while the ribs are more external. Similar, yet different are the terms superficial, and deep.

These terms are used in relation to the surface or the body. For instance, our skin is superficial to the muscles that lie deep to it. We can also use the term intermediate to express the position in between. So, a layer of fat between the skin and muscle layers could be considered intermediate.

Lastly, the terms proximal and distal are used for structures that have a beginning and an end, such as the limbs, bones, or blood vessels. In the limbs, these terms describe the relative proximity of a structure to the trunk.