Anterior corticospinal tract

The anterior corticospinal tract is an example of a descending motor tract. It comprises of upper motor neurons which helps adjust the posture by controlling the voluntary movements of the axial or truncal body musculature. Within the brain, it runs in close proximity to the lateral corticospinal tract. The latter influences the voluntary skilled (or fine) movements of the distal muscles of our body.

The corticospinal tracts–both anterior and lateral–originate from three distinct regions of the cerebral cortex, namely the primary motor cortex (pre-central gyrus, area 4), the pre-motor cortex (area 6) and the primary sensory cortex (post-central gyrus, areas 3, 1, 2). The anterior corticospinal tract is indistinguishable from the lateral corticospinal tract, at this stage. The fibers of corticospinal tract descend in the corona radiata and converge to pass through the posterior limb of the internal capsule. From here, the tract runs through the crus cerebrum or the middle cerebral peduncle of the midbrain, following which it traverses downwards through the transverse pontocerebellar fibers of the ventral pons. In the upper medulla oblongata, the corticospinal tract fibers get bundled together on either side of the midline to create swellings called the ‘pyramids’ (hence a.k.a. pyramidal tract).

In the lower medulla oblongata, majority (90%) of the corticospinal tract fibers cross (or decussate) from anterior to lateral and consequently descend in the lateral white column of the spinal cord as the lateral corticospinal tract. The remaining fibers which do not cross, descend ventrally in the lower medulla and in the spinal cord, forming the anterior corticospinal tract. The fibers of anterior corticospinal tract eventually cross the midline in their respective spinal cord segments prior to synapsing with the alpha and gamma lower motor neuron cell bodies in the anterior horns of the spinal cord.