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Rostral vs Caudal

Meaning and difference between the directional terms rostral and caudal.

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Front, back, up, down – describing locations in anatomy can sometimes be really confusing. Who knew there could be so many names for so many directions? In this short tutorial, we're going to explain two terms for you – the words rostral and caudal. To understand the terms rostral and caudal, let's quickly go over some directional terms you may already know.

Remember our lady in the anatomical position? For those who don't remember, let's quickly remind ourselves. The anatomical position is the position from which we derive all of our directional terms, and as you can see, our image is of a standing body looking straight ahead, feet apart, and pointing forward. Her arms are hanging down at both sides with palms facing forward. And if you recall, there are four important directions that are used regularly in anatomy. Can you name any of them? If you named north, south, east, and west, you're close but not quite.

The four main directions are superior, that is towards the head; inferior or towards the feet; anterior or ventral, which refers to the direction towards the stomach; and posterior or dorsal, which refers to the direction towards the back. Got that? All right, let's move on now to discuss how the terms rostral and caudal fit into all that.

So let's for a moment go back – way back. Remember this little guy? That’s right. Not long after we're little grape bunches of replicating cells, we turn into embryos. Now here's the thing. If I told you that rostral comes from the Latin word rostrum which means “beak”, where do you think the rostral end of this embryo might be? That’s right! The rostral end refers to the superior or cranial aspect of the embryo. In fact, rostral not only sounds like nostril, it can help you remember that the rostral direction is in the direction towards the nose.

So can you now guess where the caudal end might be? That’s right! It’s at the inferior or posterior end of the embryo. Caudal comes from the Latin word caudum meaning “tail.” So if we're talking about the caudal end of something, we're talking about its inferior or posterior end.

So the terms rostral and caudal are important when discussing the rostrocaudal axis in the embryo, but really where they’re used most in the human body is within the field of neuroanatomy. Let’s now have a look at how we use rostral and caudal within the brain.

For this part of the tutorial, we're going to be using this midsagittal section of the brain and, of course, when it comes to labeling our directions, we have the superior aspect over here, the inferior aspect over here, the anterior or ventral aspect over here, and our posterior or dorsal aspect over here. When it comes to neuroanatomy, the use of rostral and caudal is different for different parts of the brain and I know this is going to be a little bit confusing, but don't worry we're going to take it really slow.

The use of rostral and caudal in the brain is separated by the structure over here – the midbrain. To make things easier, let's draw a line going through the midbrain from anterior to posterior. This line is known as the midbrain diencephalic junction and occurs embryologically at the cephalic flexure. We’ll come back to some embryology a little bit later in the tutorial.

So let's start by talking about some structures including the midbrain and below. So if you remember our directions – superior, inferior, anterior or ventral, and posterior or dorsal, we can see that the terms rostral and caudal can be used in place for superior and inferior respectively. However, when talking about the structures above the midbrain, the terms rostral and caudal change direction. Ah what? I hear you ask. Don’t worry it's not as bad as it sounds. Well, I hope.

So above the midbrain, anterior remains anterior as does posterior, superior, and inferior. If you remember with the midbrain and below, we said that rostral was equivalent to superior. Well, in the cerebrum, the rostrocaudal axis takes a roughly 90-degree turn – meaning rostral is instead equivalent to anterior. Likewise, caudal goes from meaning inferior in the midbrain and below to posterior in the cerebrum. So why is this? I hear you ask.

Well, it's a tad complicated and I'll leave the nitty-gritty details for another day, but long story short when the central nervous system is developing in the embryo, it develops along what is known as the neuroaxis. Due to reasons related to our bipedal nature, the orientation of the neuroaxis changes at the junction of the midbrain and diencephalon. This results in a bending of the neural tube during development known as the cephalic flexure which is why our directions change orientation.

The image on the left shows us how the rostrocaudal axis flips within the region of the brain. The image on the right shows us the orientation of directions in relation to the neuroaxis within the entire body. In quadruped animals, there's no folding of the neural tube during embryological development so you can see how the neuroaxis is maintained along the anterior-posterior axis. It’s for this reason that the term rostral is more commonly used in veterinary science.

Now you're an expert on rostral and caudal. I hope you enjoyed our tutorial and feel confident in your knowledge about the directional terms of anatomy. If you need more help, feel free to head over to our websites to check out our full video tutorial on this very subject. And don't forget to explore our website further where you’ll also be able to find hundreds of more videos, challenging quizzes, and articles.

Thanks for watching. Happy studying!

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