The Gyrencephalic Brain: Gyri and Functional Areas
The Gyrencephalic Brain: Gyri and Functional Areas
Objective 3: Label the major gyri and functional areas of the cerebral cortex.
On either side of the central sulcus are two parallel, almost identical-looking gyri. The first we’ll look at is the precentral gyrus (part of the frontal lobe). The precentral gyrus is involved in the motor system, which has an orderly map of the body distributed across the surface of the gyrus. If you make a conscious movement, the signal needed for each muscle is calculated in this area and then sent as a neural signal down to the α motor neuron in the anterior horn of the spinal cord. Because this pathway goes from cortex to spinal cord, it’s called the corticospinal tract.
The postcentral gyrus processes sensations from the face and body surface (the somatosensory system). Like the motor cortex, it has an orderly map (homunculus) which is shown here.
Returning to the cerebral cortex, now that we have some landmarks and lobes in mind, we can begin to further subdivide the cortex. The most common mapping system for the cortex was developed by Korbinian Brodmann in the late 1800s and early 1900s.
Brodmann was a German scientist who started slicing a brain and looking at the sections through a microscope. It’s surprising, as shown in the multicolored map developed in 2016 by Glasser and van Essen, how much modern maps resemble the classic map of Brodmann.
For no reason that we can fathom, Brodmann started at the top and cut horizontal sections. Most of the cerebral cortex has six layers of cells, but the way the cells are packed and the shape of the cells are different in different places. The first pattern of cell shapes and packing he named Area 1; the second, Area 2; and so forth. The last area he numbered was Area 52.2
Some of the areas are synonymous with functional areas of the cortex and are still used today; others are obscure. Some of the area numbers you will frequently encounter are listed.
Parietal Lobe
Areas 3, 1, and 2 (postcentral gyrus): primary somatosensory cortex, receiving information about the face and body surface. No one knows why we list them in this order. Taste is also here, and nearby in area 43.
Frontal Lobe
Area 4: (precentral gyrus): primary motor cortex, sending axons to the α motor neurons of spinal cord (executing movement). This is shown in the green shading in the illustration above.
Area 6: supplementary motor area (planning or imagining movement). This is blue and purple in the illustration above.
Area 8: frontal eye fields (eye movements). This is brick-red in the illustration above.
Areas 44 and 45: Broca’s area. In most people, Broca’s area on the left side is responsible for the production of speech (movements of the throat and tongue).
The non-motor areas of frontal cortex, in the rostralmost part of this large cortical lobe, are called prefrontal cortex. Prefrontal cortex is important for holding on to our personality and individuality, the things that make you “you”.
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