This is the 2007 version. Click here for the 2017 chapter 02 table of contents.

CNS Development in the Embryo

The human nervous system starts as a tube of cells in the developing embryo. Over the first few weeks of development, the front part of the tube thickens. Already the three basic divisions of the central nervous system are visible: the forebrain, midbrain, and hindbrain.

What areas of the brain are visible in the embryonic CNS?

CNS Development in the Embryo

Late in embryological development the convolutions begin to form, giving the human brain its distinctive wrinkled appearance. The convolutions continue to form and deepen for years after a baby is born.

What causes convolutions to form? What is a fissure? A gyrus?

The convolutions form because the rapidly growing brain has different layers of cells that grow at different rates, causing buckling. Because of this folding, the brain appears to have distinct parts called lobes. Fissures—deep folds in the surface of the brain—mark off each lobe. The opposite of a fissure is a gyrus (plural gyri ), which is an outward fold similar to a hilltop on the brain. The following figure shows major gyri on the human brain.

Gyri on the Brain

The cerebrum (pronounced either SARAH-brum or suh-REE-brum) is the topmost part of the brain. It consists of everything you see in this figure. The prefrontal area, darkened above for emphasis, is an important area for higher-level thought processes in humans.

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