Anterior horn of spinal cord

The anterior horn of spinal cord, a component of the spinal gray matter, is located anterior (ventral) to the central canal. It is motor in function and is the place from where the motor information exits the central nervous system via efferent neurons to reach effector organs, such as muscles and glands.

Extending throughout the length of the spinal cord, the anterior horn consists of distinct laminae — specifically, lamina VIII and lamina IX — as defined by the cytoarchitectural characteristics of the cells in this region.

The anterior horn of spinal cord contains three main groups of nuclei: the medial, central, and lateral groups. The medial cell group innervates structures near the midline, while the lateral group innervates structures farther away from the midline, such as limb musculature. The central group, lies in between these two.

The structure and function of the anterior horn of spinal cord differ across the cervical, thoracolumbar, and sacral regions of the spinal cord. In the thoracic region, the anterior horns are smaller due to fewer motor neurons being required to control trunk musculature. Here, the medial nuclear group is present, but the lateral group is absent, as there is no need to innervate limb muscles. The central group is not prominent in this region either.

In contrast, the cervical and lumbo-sacral regions exhibit larger anterior horns due to an increased gray matter volume, housing additional neurons responsible for innervating the musculature of the upper and lower limbs via the brachial and lumbosacral plexuses, respectively. In these regions, prominent lateral nuclei are present, reflecting the functional need to control limb movements. The medial nuclear group is also well-developed in the cervical spinal cord, playing a role in innervating neck muscles. Additionally, the cervical region contains a notable central nuclear group, which includes the phrenic nucleus (essential for diaphragm innervation) and the spinal accessory nucleus (innervating the trapezius and sternocleidomastoid muscles). Fibers from the spinal accessory nucleus exit the spinal cord, ascend through the foramen magnum, and join with the cranial accessory nerve.

In the lumbosacral region, another important central group, the lumbosacral nucleus, is present within segments L2 to S1, although the specific axonal distribution of this nucleus is not well understood. The sacral anterior horns also feature a prominent medial cell group, which is responsible for innervating the perineal muscles.