Structure
The spinal cord is composed of two types or regions, the inner gray matter and the surrounding white matter. White matter is rich in myelinated axons and this results in a whiter visual appearance in unstained tissue, relative to the darker gray matter. When viewed in cross section, white matter is essentially all of the spinal cord other than the central butterfly shape of gray matter. White matter is composed of dense tracts of neuronal axons that are heavily myelinated by glial cells known as oligodendrocytes. These bundles or tracts of fibers, sometimes referred to as fasciculi, carry information up towards the brain or down to the appropriate spinal cord level.
Key Features/Anatomical Relations
The spinal cord white matter varies in thickness depending on location, with the upper cervical levels having more white matter and the sacral regions having the least. This is due to the fact that all information to the entire body must travel up and down through cervical levels, while only information pertaining to lower limb and genital regions is found in the sacral levels.
The white matter is broken down into three major regions, or funiculi. The dorsal funiculus lays dorsal to the gray matter, the lateral funiculus is located lateral to the gray matter, and the ventral funiculus is located ventral to the gray matter. Within each region multiple tracts, each of which is called a fasciculus, carry information that is either ascending or descending.
List of Clinical Correlates
- Paralysis
- Hypertonia
- Spasticity
