Learning Neuroanatomy made easy - Subcortical region of the brain
- Aparajitha
- Apr 7, 2023
- 3 min read
The cerebrum is at the top and the brainstem is at the bottom, and everything in between is referred to as the subcortical region. These structures can be easily oriented by just learning two diagrams of the brain - the coronal and the sagittal section.
To be honest, I had a lot of trouble wrapping my head around the depiction of a three-dimensional structure into a two-dimensional figure. The purpose of this blog article is to break down these two diagrams in a simple and understandable manner.
We are going to reconstruct a model step by step. Lets start with our first structure - Fig 1. This is the base upon which we will build the model.
Place this image in a 3D environment. The little rounded structures in the anterior aspect are the mammillary body, and the oval structure in the posterior aspect is the hippocampus. And the fornix is the link between the two. The Amygdala is the structure on top of the hippocampus. The fornix on the Right and left are connected by a commissure (Fig 2)
The next stage is to visualize the thalamus and basal ganglia structures as cups stacked on top of one another. Just like the picture depicted below.
Let us now include the Thalamus on one side of the fornix. Consider the thalamus as a snug fit within the space created by the fornix. The globus pallidus interna and externa are next added, followed by the putamen. These structures are built laterally on top of the thalamus. The caudate structure is built superiorly to all of these structures (Fig 3, 4)
The next structure that is placed superiorly to all these existing structures is the corpus callosum. The corpus callosum and the fornix are attached by a sheet called septum pellucidum. (Fig 5)
Time to check out the complete image. It looks cool! (Fig 6)
Viewing it from the side gives us a picture like this. This is the coronal section of the brain.
Those three black circular structures are Anterior, posterior and habenular commissures (Fig 7). Check out my post on commissural fibers to learn more.
Keeping these fundamentals in mind, let us now model the sagittal portion of the brain (Figure 8)
If you're still confused, let us walk you through it step by step.
On top, we begin by drawing the corpus callosum and the septum pellucidum, which link to the fornix. The fornix seems circular because a sliced cylinder appears circular when viewed from the front. The other corresponding parts - mammary body and the hippocampus which form the bulb like structures on either ends of the fornix are drawn down below. Next, adding our favorite thalamus below the fornix followed by the colorful bowls of Globus pallidus and putamen. As caudate comes on the top of these structures, it is drawn over it (Fig 9).
Some structures that are frequently overlooked in a coronal slice can be seen clearly when studying the sagittal section. The CSF system is shown in blue - the lateral and third ventricles. The lateral ventricle is between septum pellucidum and the thalamus which extends downward as third ventricle.
The thalamus and the lentiform nucleus is separated by white matter called the internal capsule containing all the tracts to and from the cerebral cortex. Lateral to the lentiform nucleus are some more tracts and are referred to as the external capsule. Lateral to the external capsule, is an interesting structure called claustrum (Fig 10). Learn more about claustrum from this article.
And that's it! You have now mastered the coronal and sagittal section of the brain.
Hope you found this post interesting and fun.
References
Gray, H. (2013). Gray’s Anatomy: With original illustrations by Henry Carter. Arcturus Publishing.
Crick FC, Koch C. What is the function of the claustrum? Philos Trans R Soc Lond B Biol Sci. 2005 Jun 29;360(1458):1271-9. doi: 10.1098/rstb.2005.1661. PMID: 16147522; PMCID: PMC1569501.
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