The Development of the Chordate Nerve Cord

Why is the chordate nerve cord described as hollow when it appears to be solid?

The chordate nerve cord is often described as “hollow” because its structure initially appears solid when observed under a microscope. However, the term “hollow” refers to the fact that the nerve cord is not a solid mass of tissue, but rather contains a fluid-filled cavity, known as the neural canal or neural tube.

During development, the chordate nerve cord begins as a solid structure called the neural plate, which folds inward to form a groove called the neural groove. As the neural groove continues to deepen, the edges of the groove eventually fuse together, creating the neural tube. This tube gives rise to the central nervous system, including the brain and spinal cord.

The neural tube is considered “hollow” because, after fusion occurs, the center of the tube is filled with cerebrospinal fluid (CSF), providing cushioning and support to the developing nervous tissue. CSF also plays a vital role in nutrient supply and waste removal within the nervous system.

Although the outer layer of tissue in the nerve cord may appear solid, it actually surrounds this fluid-filled hollow core. This central channel is what makes the nerve cord be referred to as a “hollow” structure.

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