Hear This Illustration: the Locations of Selected Sensory and Motor Tracts, Shown in A

Hear This Illustration: The locations of selected sensory and motor tracts, shown in a transverse section of the spinal cord

This transverse section of the spinal cord illustrates functions of the white matter areas of the spinal cord. The white matter is generally subdivided into anatomical regions known as columns. Histological cross sections of the spinal cord show that the white areas contain little more than myelinated axons. The axons concentrated in the areas shown in red are conducting sensory information that ascends toward the brain for interpretation. In blue, the concentrations of axons are carrying information that descends from the brain to control the muscles.

Ascending, sensory tracts are generally named according to their location in the spinal cord and include terms such as lateral or medial. Most importantly, the names describe the region of the brain where this sensory information will be processed. Each of these tracts conducts different kinds of sensory information. Names of the descending, motor tracts, shown in blue, reflect their location in the spinal cord or where the neurons controlling that muscle activity arise or take major anatomical detours.

These two groups of ascending and descending tracts occur on both sides of the spinal cord but are shown separately here to simplify the diagram. Once you have studied these patterns, you might want to fill in the corresponding red and blue areas on your own.