Anatomy of the ascending spinal cord pathways

The spinal cord is like a highway that enables a two-way communication between the brain and other parts of the body. It contains neural pathways, called spinal cord pathways, or simply spinal tracts, which can be either ascending or descending. Both types of tracts are made up of neuronal axons that gather into long columns called funiculi, which are found inside the ventral, lateral and dorsal aspects of the spinal cord. Here, we’ll focus on the ascending tracts, which are sensory pathways, carrying sensory information from the body, like pain, up the spinal cord to the brain.

Now, let’s start by looking at the anatomy of the spinal cord. Anteriorly, there is a deep midline depression called the ventral median fissure and, posteriorly, there is a more shallow midline depression called the dorsal median sulcus. ​​Each half also has a ventrolateral sulcus, where ventral rootlets leave the spinal cord; and a dorsolateral sulcus, where dorsal rootlets enter the spinal cord. The ventral and dorsal rootlets fuse to form the ventral and dorsal roots, respectively.

Ventral rootlets and roots carry motor fibers that travel from the spinal cord to different organs and muscles, while their dorsal counterparts - with a sensory ganglion, called the dorsal root ganglion, attached to each dorsal root - carry sensory fibers from organs and receptors throughout the body to the spinal cord.

Now, on a transverse section, the spinal cord has an area of gray matter shaped like a capital “H” in the middle. The gray matter is subdivided into the gray commissure, which is the strip connecting the two halves of the spinal cord that surrounds the central canal; and the peripheral regions known as horns.

There are two ventral, and two dorsal horns. Dorsal horns contain neuronal cell bodies that process information received from sensory fibers, entering the spinal cord from the dorsal roots and dorsal rootlets. On the other hand, the ventral horns contain cell bodies of motor neurons, with motor fibers exiting through the ventral rootlets and ventral roots.

Now, the gray matter in the T1 through L3 spinal cord segments has a small lateral projection known as the lateral horn. The lateral horn is located between the dorsal and ventral horns, and contains the cell bodies of preganglionic neurons of the sympathetic nervous system, which mediates the fight-or-flight response, including increasing heart rate and dilating bronchioles to increase air intake. The gray matter is surrounded by white matter, which consists of bundles of axons that carry information to and from the brain. These axons are organized into bundles called tracts or pathways.