White Matter

The white matter of the spinal cord is divided into three large regions, each of which is composed of individual tracts or fasciculi. The posterior funiculus is located between the posterior median septum and the medial edge of the horn. At cervical levels, this area consists of the gracile and cuneate fasciculi; collectively, these are commonly referred to as the posterior columns.

The lateral funiculus is the area of white matter located between the posterolateral and anterolateral sulci. This region of the cord contains clinically important ascending and descending tracts. Those most important in diagnosis of the neurologically impaired patient are the lateral corticospinal tract and the anterolateral system (ALS).

Located between the anterolateral sulcus and the ventral median fissure is a comparatively small region, the anterior funiculus. This area contains reticulospinal and vestibulospinal fibers, portions of the ALS, the anterior corticospinal tract, and a composite bundle called the medial longitudinal fasciculus (MLF).

Two small but important components of the white matter are the anterior white commissure and the posterolateral (dorsolateral) tract. The anterior white commissure is located on the anterior midline and is separated from the central canal by a narrow band of small cells. The posterolateral tract, the tract of Lissauer, is a small bundle of lightly myelinated and unmyelinated fibers capping the posterior horn.