The central canal of the spinal cord is a microscopic, narrow channel that extends longitudinally through the core of the spinal cord. This continuous passage runs from the lower part of the brainstem down to the tip of the spinal cord, known as the conus medullaris.
Anatomical Location and Structure
The central canal is positioned within the gray matter of the spinal cord, residing in the center of the gray commissure. This commissure is a bridge of gray matter that connects the two butterfly-shaped halves of the spinal cord’s central region.
The interior of the central canal is lined by a specialized layer of cells called ependymal cells. These neuroglial cells are typically columnar and possess small, hair-like projections known as cilia on their surfaces. These cilia contribute to the movement of fluid within the canal. The ependymal cells also form a barrier, regulating the exchange of substances between the fluid within the canal and the surrounding spinal cord tissue.
Role in Cerebrospinal Fluid Circulation
Within the central canal flows cerebrospinal fluid (CSF), a clear, colorless liquid that bathes the central nervous system. This fluid-filled channel directly connects to the ventricular system of the brain, specifically being continuous with the fourth ventricle located in the brainstem.
Cerebrospinal fluid performs several functions, including providing mechanical protection by cushioning the brain and spinal cord against physical impacts. It also facilitates the transport of nutrients and signaling molecules to nervous tissue and aids in the removal of metabolic waste products. In adults, the actual volume of CSF flow within the central canal is very small.
Development and Changes Over a Lifetime
The central canal originates from the neural canal, which is the hollow interior of the embryonic neural tube during development. This neural tube forms early in embryonic life, around the fourth week of gestation, and eventually differentiates into the brain and spinal cord. The neural canal’s lumen gradually narrows as the walls of the neural tube thicken, resulting in the minute central canal observed in the adult spinal cord.
With advancing age, the central canal undergoes significant changes. While it is fully patent (open) in infancy, its patency rate decreases markedly after the first decade of life. In many adults, the canal becomes very narrow or may even close off completely in certain segments, a process referred to as stenosis or obliteration. This narrowing or closure is a common and expected part of the aging process and is not typically associated with any symptoms or health concerns.
Associated Medical Conditions
Although often a normal structure, the central canal can be involved in certain medical conditions. One primary condition is syringomyelia, characterized by the formation of a fluid-filled cyst, known as a syrinx, within the spinal cord. This syrinx often represents an abnormal expansion of the central canal itself, as cerebrospinal fluid collects within the spinal cord tissue.
Syringomyelia can arise from various causes, including congenital conditions like Chiari malformations, where brain tissue extends into the spinal canal and disrupts CSF flow. Other causes include spinal cord trauma, tumors growing on or near the spinal cord, and inflammation of the arachnoid membrane, one of the protective layers surrounding the spinal cord. Symptoms typically develop slowly over years and vary depending on the syrinx’s location and size, often including pain, progressive weakness, stiffness in the limbs or back, loss of sensitivity to temperature or pain, and headaches.
Another condition involves tumors that can originate from the ependymal cells lining the central canal, known as ependymomas. These are primary central nervous system tumors that can occur in both children and adults, with spinal ependymomas being more common in adults. As ependymomas grow, they can press on surrounding spinal cord tissue or obstruct CSF flow. Symptoms of spinal ependymomas can include back pain, numbness, weakness in the arms, legs, or trunk, and sometimes problems with bladder or bowel control. These tumors can also spread to other areas of the brain or spine through the cerebrospinal fluid.