Anatomy of the basal ganglia

Generally speaking, our central nervous system is made up of three parts; the cerebrum, the cerebellum, and the brainstem. The cerebrum consists of two nearly symmetrical halves called the cerebral hemispheres, and deep within these hemispheres lie the basal ganglia.

On a coronal or axial section of the brain, the outermost area represents the cerebral cortex, which is made up of gray matter that consists of billions of neuronal cell bodies. The axons that are connected to these cell bodies create the white matter of the brain, which is the innermost area.

One prominent white matter fiber bundle is the internal capsule, which is like a highway that allows signals, and thus information, to flow to and from the cerebral cortex. On both sides of the internal capsule, we can see areas of subcortical gray matter that form the basal ganglia.

The basal ganglia are very important for providing a feedback mechanism to motor cortices for initiation and control of voluntary movements. So, for example, you want to write your name on a piece of paper.

First, you plan the movements using your prefrontal cortex, and that sends a signal to the motor cortex as well as the basal ganglia. The basal ganglia now help the motor cortex prepare for, and initiate the action. The result is that you position your arm so that you can start writing.

Then, the basal ganglia ensure that your hand movements are as precise and executed as planned, and while doing so, they also maintain your posture. In addition to this, the basal ganglia can help you learn new procedural motor skills, like riding a bicycle.

The basal ganglia are a collection of nuclei that include the caudate nucleus, the putamen, the globus pallidus externus and the globus pallidus internus. These nuclei have highly complex connections with other parts of the central nervous system, like the cerebral cortex, the thalamus and the brainstem. But the two most important structures that are closely related to the basal ganglia are the substantia nigra of the midbrain and the subthalamic nuclei of the diencephalon.