Okay this is a tutorial on anatomical terms, and it's a basic tutorial which should hopefully help you to understand how different terms in anatomy are used to describe the relative positions different structures in the body.
Firstly, I'm going to talk about the anatomical position. This model here is standing in the anatomical position, you can see he is standing facing forwards with his face looking towards you, his palms are facing outwards and his forearms are supinated, and his feet are facing forward like that. This is the anatomical position, and if I just zoom in a bit on his head, technically speaking, in the anatomical position, the inferior margin of the orbit should be level with the top of the external auditory meatus.
That’s just a technical detail. When you describe anatomical structures, you talk about them with reference to this anatomical position; the little finger is medial to the thumb. You can imagine if, even if the hand is facing the other way, the patient is laying on the bed, upside down standing on their head, whatever, you're always talking about structures relative to the anatomical position.
Firstly I'm just going to talk a little bit about anatomical planes, because people tend to talk about them. They’re three major groups of planes in the human body, the sagittal plane, the coronal plane and the axial plane or the transverse plane - transverse, horizontal, axial are used interchangeably. the sagittal plane is a plane that divides the body into left and right halves. And it runs straight down the middle here.
The coronal plane is oriented vertically and divides the body into anterior and posterior halves. And it runs perpendicular to the sagittal plane, it runs down here. And then the horizontal, transverse, axial, whatever you want to call it, plane, runs as you could probably guess - horizontally, and it divides the body into superior and inferior parts. Just going back to the sagittal plane, the plane that divides the body exactly equally into right and left halves is known as the median sagittal plane.
When you learn about anatomy, or you're reading textbooks or watching these tutorials, you'll hear a lot of terms that are thrown about to help describe the relative locations of structures within the body, like anterior, posterior, superficial, deep, proximal, distal, superior, inferior, rostral, caudal, dorsal ventral. All these kinds of words.
Anterior and Posterior
I'll just run through what these mean and I'll show you a few examples, hopefully you'll be able to remember what these all mean in the future. Anterior and posterior - anterior means closer to the front of the body, and all these terms are relative to the anatomical position, anterior and posterior describe structures relative to the front and the back of the body.
For example, the sternum is anterior to the heart, I’ll just show you that. The sternum here, just zoom in a bit, is anterior to the lungs, it's anterior to the heart, anterior to the vertebrae, or you could say the vertebrae is posterior to the sternum, whatever you like. Anterior and posterior refer to the front and the back of the body.
Medial and Lateral
Medial and lateral means close to, medial is close to the midline, and lateral is further away from the midline. A medial structure is a structure that is closer to that median sagittal plane that I talked about a bit before.For instance, going back to the sternum, dunno why I'm choosing the sternum but, the sternum is medial to the humerus, the sternum is medial to the ribs. medial and lateral just refer to either closer, or further away to the midline. And just going back to the importance of the anatomical position, we would say that the little finger is medial to the thumb, because in the anatomical position, the little finger is closer to the midline.
Obviously you can see that if this model was to turn his palm, so they were facing away from you, then the thumb would be closer to the midline, but we would still say that the thumb is a lateral structure, relative to the little finger, because in the anatomical position that's how it is. Always describe things relative to the anatomical position.
Superior and Inferior
Superior and inferior describe things on the vertical axis, a superior structure is one that is closer to the top, and an inferior structure is one that is closer to the bottom, we could say that the nose is superior to the chest, the nose is superior to the knees, the knees are superior to the feet. That’s what superior and inferior mean.
Superficial and Deep
Another term that is used quite a lot is superficial and deep. Superficial just means close to the surface of the body, and deep means further away from the surface of the body. If I just move, I'm just going to move the slider on the left which is slightly off screen at the moment, and it will move gradually from superficial to deep structures. Going down to the muscle layer, down the bones, and then you can see the organs and moving everything, going from superficial to deep and then back to... where this might be a bit confusing is if you are describing structures on the back, the skin here is superficial but it is posterior.
This is a muscle of the back here, if you're looking at the muscles of the back, the latissimus dorsi is a posterior structure, but it is more superficial than lie underneath it, the serratus posterior inferior is deep to the latissimus dorsi, but it is more anterior than the latissimus dorsi, because relative to the anatomical position it's closer to the front of the body. Superficial and deep are just used to describe things closer to the surface of the body or further away from the surface of the body, the heart is deep to the skin.
Proximal and Distal
The words proximal and distal are also commonly used, especially when talking about the limbs and the digestive tract, or anything, well a lot of things really, but proximal means closer to the trunk or closer to the structure's origin and distal means further away from the structures origin.
If we're just talking about muscles, for instance, the proximal attachment is here, and the distal attachment of the biceps is here. The shoulder is proximal to the elbow. The phalanges are distal to the elbow. proximal and distal refer to a structures origin. If we're talking about the digestive system for instance, I'll just get that up, the digestive system origin, the mouth, is the most proximal part of the digestive system, and oh, didn't mean to click that.
And the anus is the most distal part of the digestive system, we could say that the stomach is distal to the oesophagus. We could say the anus is distal to the stomach; the stomach is proximal to the anus.
Origin and Insertion
With reference to muscles, you often hear the words origin and insertion, the origin is the proximal attachment and the insertion is the distal attachment.
The origin is attached to the unmovable bone, and the insertion is attached to the movable surface of the bone. In the example of the biceps, just look at that, the short head of the biceps - this is the origin, its proximal - i.e. closer to the trunk.
That's the proximal attachment, and the distal attachment, the distal attachment is down here, that's the insertion, and it's inserted on to the bone which moves, and this is the bone which doesn't move, that's the origin and that's the insertion. And it's used for other, as well as the digestive system and muscles, it's used to describe blood vessels, you can say, the, the origin of blood vessels, you could say the radial artery is distal to the subclavian artery, because the subclavian artery is closer to the origin. That’s proximal and distal. we've talked about anterior, posterior, proximal, distal, medial, lateral, superior inferior.
Sometimes you'll hear the words dorsal, ventral, rostral and caudal. In human anatomy, this is usually restricted to use, to being used when referring to the nervous system, in the spine, you may hear of dorsal roots and ventral roots, and here it's referring to posterior and anterior.
Dorsal and Ventral
Dorsal is posterior and ventral is anterior. But in the brain, these words have a slightly different and specific meaning, if I just zoom into the brain; I'll show you what these words mean.
Rostral and Caudal
In the brain you'll hear the words rostral and caudal, rostral is anterior, and caudal is posterior. Dorsal is superior, and ventral is inferior, and that's primarily used in the brain in human anatomy. And then in the spinal cord, dorsal is posterior and ventral is anterior, that's a little bit confusing, but it's useful to be aware of, before you start hearing it and getting confused.
I think I've covered most of the common planes, and the terms to describe location, hopefully that will be useful and you'll remember what these mean when you hear them being used. Thank you for listening.