The four major regions of the brain

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As is the case with many other human organs, understanding the structures and anatomy of the brain has proven far easier than understanding its functioning and physiology. As a result, different neuroanatomists have organized and labelled the different parts of the brain in different ways, based on different criteria. You can organize the brain by specific locations and structures, by related functions, by similar cytological features, etc. Often, the same region of the brain can have various names, depending on what system of organization you are using at the time.

We will mainly organize the brain by its gross anatomy – its large structures that are visible to the eye.

The human brain can be divided into four major parts, illustrated in Figure 10-2 and Figure 10-3.

  1. The cerebrum, which is the part with the folds and crevices that we most associate with a mental image of the brain. It consists of two cerebral hemispheres which are divided by the longitudinal fissure down the center of the cerebrum.
  2. The cerebellum, which is also known as the hindbrain. It is in the posterior region of the brain and inferior to the back of the cerebrum. In cross-section, it has an almost-cauliflower appearance, while its exterior consists of thin parallel folds.
  3. The brain stem connects directly to the spinal cord but is noticeably thicker than the spinal cord below it.
  4. The diencephalon is in the interior of the brain and can only be seen in its entirety if the brain is cut open. In intact brains, only the floor of the diencephalon can be seen directly superior to the brain stem.
The major regions of the brain.

Figure 10-2. The cerebrum, the cerebellum, and the brain stem are the three major regions of the brain visible from the exterior.

 

Diencephalon

Figure 10-3. Two views of the diencephalon, the fourth major region of the brain, in orange on the left and in orange and green on the right.