Organization of the central nervous system

The human spinal cord has about 10⁸ neurons. A transverse section through the spinal cord shows a butterfly-shaped central gray matter which contains neuron cell bodies. The white matter surrounding the gray is largely axons in ascending and descending 14tracts and gets its color from the high content of myelin. In the middle is the central canal which contains cerebrospinal fluid (CSF), though in adults it is usually closed.