General Structure and Central Canal
Unlike the white matter located peripherally, which consists of ascending and descending tracts, the gray matter is situated strictly in the center of the spinal cord. Its tissue framework is composed of neuronal cell bodies, unmyelinated nerve cell processes, neuroglial elements, and blood vessels.
In the exact center of the gray matter lies the central intermediate gray substance (substantia (grisea) intermedia centralis). Running through its core is the central canal (canalis centralis). This canal extends along the entire length of the spinal cord:
- Superiorly, it opens into the cavity of the fourth ventricle of the brain.
- Inferiorly (in the region of the conus medullaris), the canal widens.
- Throughout its entire length, the canal is surrounded by specialized central gelatinous substance (substantia gelatinosa centralis).
Spatial Organization: Gray Columns and Horns
The longitudinal columns of gray matter running along the spinal cord form volumetric structures known as gray columns. On a transverse cross-section, these columns form the so-called horns (cornua).
Three main divisions are distinguished:
- Anterior column (columna ventralis / anterior). On cross-section, it forms the anterior horn (cornu ventrale / anterius). This is a broad structure that does not reach the outer surface of the spinal cord.
- Posterior column (columna dorsalis / posterior). Forms the posterior horn (cornu dorsale / posterius). Unlike the anterior horn, it is narrow, long, and reaches the outer surface. The structure of the posterior horn comprises three parts: the apex, neck, and base.
- Lateral column (columna lateralis). Forms the lateral horn (cornu laterale), which is prominently expressed primarily in the thoracic segments.
A special zone is located between the lateral horn and the lateral margin of the posterior horn. Here, gray matter projects into the white matter, forming the spinal reticular formation (formatio reticularis).
Nuclei of the Spinal Cord Gray Matter
The neurons of the gray matter are not randomly scattered, but are grouped into nuclei with strict and constant topography. Depending on their localization within a specific column, these nuclei perform various functions: motor, sensory, or autonomic.
Nuclei of the Anterior Column (Motor)
| Nucleus Name | Latin Term | Localization (Segments) |
|---|---|---|
| Ventrolateral nucleus | nucleus ventrolateralis | CIV–CVIII and LII–SI |
| Ventromedial nucleus | nucleus ventromedialis | CII–LIV |
| Dorsolateral nucleus | nucleus dorsolateralis | CV–CVIII and LIII–SII |
| Dorsomedial nucleus | nucleus dorsomedialis | CI–SII |
| Central nucleus | nucleus centralis | ThI–LIII (occasionally SI–SV) |
| Accessory nerve nucleus | nucleus nervi accessorii | CI–CVI |
| Phrenic nerve nucleus | nucleus nervi phrenici | CIV–CVII |
| Lumbosacral dorsal nucleus | nucleus lumbodorsalis | LIII–SI |
Sensory and Autonomic Nuclei
The posterior and lateral columns house centers responsible for sensory perception and autonomic regulation of body functions.
Nuclei of the Posterior Column (Sensory)
Three key structures are distinguished here:
- Gelatinous substance (substantia gelatinosa);
- Proper sensory nucleus of the posterior horn (nucleus proprius cornus posterioris);
- Secondary visceral gray matter (substantia visceralis secundaria).
Nuclei of the Lateral Column (Autonomic)
These nuclei are localized predominantly in the thoracic and sacral regions:
- Thoracic nucleus (nucleus thoracicus [Clarke's column]) — located in segments ThI–LII.
- Central intermediate substance (substantia intermedia centralis).
- Lateral intermediate substance (substantia intermedia lateralis).
- Sacral parasympathetic nuclei (nuclei parasympathici sacrales) — located in segments SII–SIV.