Lumbar part of spinal cord

The lumbar part of spinal cord lies between the cervical and thoracic parts above and the sacral, and coccygeal spinal regions below.

Like all other regions, the lumbar part of spinal cord consists of a central butterfly shaped gray matter with anterior (motor) and posterior (sensory) gray columns or horns. The lumbar part of spinal cord (similar to the cervical part) is distinct from other regions of the cord, as it has more gray matter (hence, bigger anterior and posterior horns) due to additional neurons that are required to innervate the lower limbs.

The anterior gray horn of the lumbar spinal cord is characterized by a prominent lateral cell group, which is responsible for innervating the muscles of the lower limbs. Additionally, a central group of neurons, known as the lumbosacral nucleus, extends from the L2 to S1 spinal segments. Unlike the thoracic spinal cord, the lumbar spinal segments lack a medial cell group which was specialized for innervating midline structures, such as the trunk musculature.

The posterior gray horn of the lumbar part of spinal cord, like that of other spinal regions, contains two primary groups of nuclei that extend throughout the length of the cord. These include the substantia gelatinosa, responsible for processesing pain and temperature sensations, and the nucleus proprius, which interprets sensory inputs related to proprioception, vibration, and two-point discrimination. Additionally, the lower terminal portion of the dorsal nucleus of Clarke is present in the lumbar part of spinal cord, as this nucleus runs from the C8 spinal segment to the L3 or L4 segments. Clarke's nucleus plays a crucial role in receiving proprioceptive information and transmitting it to the cerebellum. Lastly, the visceral afferent nucleus, involved in autonomic innervation, is located in the upper lumbar spinal segments.

The lateral gray horn, commencing at the T1 spinal segment and terminating at the L2 spinal segment, is absent in the lower lumbar part of spinal cord.

The gray matter on both sides–right and left–are interconnected by a gray commissure that surrounds a central canal, a.k.a. the spinal canal.

It is important to note that, like that of other spinal regions, the gray matter in the lumbar part of spinal cord is also surrounded by bundles of white matter fibers or tracts. These include the anterior, posterior and lateral white columns (or funiculi).

The anterior white column (a.k.a. anterior funiculus) in the lumbar part of spinal cord, similar to other spinal regions, contains sensory and motor tracts. These include the anterior spinothalamic, anterior corticospinal, tectospinal, vestibulospinal, and pontine reticulospinal tracts.

The lateral white column (a.k.a. lateral funiculus) likewise contains a combination of sensory and motor tracts, such as the anterior and posterior spinocerebellar, lateral spinothalamic, lateral corticospinal, lateral reticulospinal, and rubrospinal tracts.

The posterior or dorsal white column in the lumbar part of spinal cord differs from that in other spinal levels. It lacks the fasciculus cuneatus, as this tract is responsible for innervating the upper limbs, which are not represented at this lower spinal level. However, the fasciculus gracilis is present throughout the entire length of the spinal cord and can be identified in the dorsal column of the lumbar region.