Development of the brain and spine

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Our central nervous system contains some 100 billion neurons, the same number as there are stars in the milky way galaxy. Each neuron connects to about 10,000 other neurons, generating a quadrillion connections (1,000,000,000,000,000). But how does such complex network develops?

We all begin existence as a fairly simple thing: a single cell, in other words a tiny, spherical bag of proteins and DNA. This cell will start dividing, rapidly forming a compact group of cells, which will then differentiate in different group of tissues. At about the 16th day of development a narrow groove begins to form on the nascent group of cells, giving the first hint of a nervous system. 

The groove then folds unto itself, forming what is called the neural tube, a primitive form of our future brain and spinal cord. 

A radical transformation
The neural tube “squeezes” in various sections to form different parts of the brain and spinal cord. Around the first month of development the 4 main components of the central nervous system are formed.

Up until the moment we are born, the neural tissue will expand, fold and become more complex as each area is interconnected with the others.
In this regard, the spinal cord is more than a mere interface between our brain and the environment (sensation and movement). As it develops its internal structure becomes multi-layered and several distinct sub-areas are created.

The spinal cord – development explains anatomy
The nerves that will connect the spine to the rest of the body exit the spine transversely at an early developmental stage.

As the whole body grows the spinal nerves become oblique to the cord itself and an interesting anatomical fact appears: the different areas of the spine don’t match the height of the spinal nerves when they exit the vertebral column.
Each nerve (on both sides) will connect to a specific group of muscles (myotomes) and a specific skin area (dermatomes). This segmentation is even more apparent when a person is bending down: Four areas cover the totality of the body - cervical, thoracic, lumbar and sacral.

Knowing this it becomes obvious that the height of a spinal cord injury will have a dramatic effect on the severity of its symptoms.

Importance for regenerative medicine
When an injury occurs, this intricate system fails to regenerate. Even when the obstacles to regeneration are cleared, growing adult fibers usually fail to reform functional connections. Many scientists are exploring the possibility of somehow “mimicking” some of the stages that take place during development in order to promote a controlled and functional regeneration of the injured fibers.

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