Intermediate zone of spinal cord

Intermediate zone of spinal cord refers to the region of gray matter which lies between the posterior (or dorsal) and anterior (or ventral) horns of the spinal cord. It comprises of the central intermediate substance (Rexed lamina X) and the lateral intermediate substance (Rexed lamina X).

The central intermediate substance comprises of the gray matter that surrounds the central canal and can be divided into dorsal and ventral commissures, behind and in front of the central canal, respectively.

The central intermediate substance continues laterally as the lateral intermediate substance in between the posterior and anterior horns of the spinal gray matter. This region corresponds with the base of posterior horn of spinal cord (lamina VII). In the thoracic and upper lumbar region (T1 to L2 spinal segments) the lateral intermediate substance protrudes outwards to create an additional lateral horn of the spinal cord.

The important groups of nuclei in the lateral intermediate substance (lamina VII) include the posterior thoracic nucleus (a.k.a. the Dorsal nucleus of Clarke or Clarke’s column), visceral afferent nucleus and the intermediolateral nucleus. Most of them lie in the thoracic and upper lumbar spinal segments and do not extend throughout the length of the spinal cord.

The posterior thoracic nucleus or the Dorsal nucleus of Clarke or Clarke’s column (C8 to L3/L4 spinal segments) receives subconscious proprioceptive information from muscle spindles and Golgi tendon organs. The axons from the cells in the Clarke’s column give rise to dorsal and ventral spinocerebellar tracts, which carry the proprioceptive information to the cerebellum.

The visceral afferent nucleus is located just lateral to the Clarke’s column and is believed to be associated with receiving visceral afferent information.

An additional group of neuronal cell bodies, called the intermediolateral nucleus can be found In the region where the lateral intermediate substance protrudes outwards to create a lateral horn (from T1 to L2 spinal segments). The intermediolateral nucleus give rise to preganglionic sympathetic neuronal efferents, which synapse with the ganglia inside the sympathetic trunk or ascend / descend within the trunk to reach the target organs.

Just like the T1-L2 segments of spinal cord, a similar group of cells is also found in the intermediate zone of spinal cord, from S2 to S4 spinal segments. These cell groups give rise to the preganglionic parasympathetic autonomic motor neurons. However, there is no prominent lateral horn created by these nuclei in the sacral region.