The spinal cord is a long, cylindrical structure extending from the base of the skull, connecting the brain to the rest of the body. It is a crucial part of the central nervous system, serving as the main pathway for information transfer. The spinal cord acts as a two-way highway, relaying signals that allow the brain to control movement and the body to send sensory feedback.
Distinguishing Gray and White Matter
The spinal cord’s interior is organized into two distinct tissue types: gray matter and white matter. These tissues are named for their appearance in a cross-section and are composed of different neural components. Gray matter is located centrally, forming a characteristic “H” or butterfly shape. It consists primarily of neuron cell bodies, dendrites, and synapses, which are the main sites for processing information.
White matter is found in the outer region, completely surrounding the central gray matter core. Its lighter color is due to the high concentration of myelin, a fatty, insulating sheath that wraps around the axons of nerve cells. These myelinated axons are the long-distance “wires” of the nervous system, designed to rapidly transmit electrical signals up and down the spinal cord.
The Organization of White Matter Columns
The white matter is precisely organized into large bundles known as columns or funiculi. In a cross-section, the white matter is symmetrically divided into three paired regions on each side of the spinal cord. These regions are identified by their position relative to the central gray matter horns.
Posterior Column
The posterior column (dorsal funiculus) lies between the two posterior (dorsal) gray horns. It is separated from the lateral column where the sensory nerve roots enter the cord.
Lateral Column
The lateral column (lateral funiculus) is situated on the side of the spinal cord. It is positioned between the posterior gray horn and the anterior gray horn.
Anterior Column
The anterior column (ventral funiculus) occupies the space between the anterior gray horns, running along the front midline of the cord. This tripartite division organizes the communication pathways for specific and directional signal transmission.
What Signals Travel Through White Matter
The white matter functions as the long-distance relay system of the central nervous system. It is composed of tracts, which are bundles of axons that share a common origin and destination. These tracts carry information either toward the brain or away from it, ensuring constant communication.
Ascending Tracts
The white matter contains ascending tracts, which convey sensory information from the body up to the brain. These signals include sensations like light touch, pain, temperature changes, and proprioception (the sense of body position and movement). The pathways are highly organized, with different tracts carrying specific types of sensory data.
Descending Tracts
Descending tracts transmit motor commands from the brain down to the muscles and glands throughout the body. These signals control voluntary movement and coordinate muscle action. The organization of the white matter allows for rapid and efficient communication between the brain and the rest of the body.