Gray Matter


Gray Matter

Grey Matter is composed of neuronal cell bodies, dendrites, axons, glial cells, synapses and capillaries.

In the spinal cord, grey matter consists of horns, dorsal and ventral, and an intermediate zone.

The dorsal horns are derived from the alar plate, and consist of afferent neurons.
The ventral horns are derived from the basal plate, and consist of motor neurons whose axons run to skeletal muscles.

In addition to the already present horns, inbetween Th1 and L2 lateral horns can also be observed. These contain sympathetic(promote the fight-or-flight response) neurons that give rise  to preganglionic sympathetic fibers – run through the ventral roots to various sympathetic ganglia.

  • Root Neurons:
    • Present in the anterior and lateral horns
    • Axons exit via ventral roots
    • Innervate somatic or visceral effectors
  • Column neurons
    • Are confined within the CNS
    • Are classified on the basis of length, course and synapse as:
      • Central
      • Internuncial
      • Commisural
      • Association
    • A large number of column neurons give rise to axons that enter the white matter, bifurcate, and ascend/descend for a variable distance.

Nuclei of the posterior horn:

  1. Marginal nucleus
  2. Central gelatinous substance
  3. Nucleus proprius
  4. Posterior thoracic nucleus of Stiling-Clarke

Nuclei of the lateral horn

  1. Intermediomedial nucleus
  2. Intermediolateral nucleus

Nuclei of the anterior horn

There are 5 motor nuclei.

Columns, according to Grey:

Most of the nerve cells are arranged in longitudinal columns, and appear as groups on transverse section. 

Nerve Cells in the Lateral Column.—These form a column which is best marked where the lateral gray column is differentiated, viz., in the thoracic regionbut it can be traced throughout the entire length of the medulla spinalis in the form of groups of small cells which are situated in the anterior part of the formatio reticularis. In the upper part of the cervical region and lower part of the medulla oblongata as well as in the third and fourth sacral segments this column is again differentiated. In the medulla it is known as the lateral nucleus. The cells of this column are fusiform or star-shaped, and of a medium size: the axons of some of them pass into the anterior nerve roots, by which they are carried to the sympathetic nerves: they constitute the white rami and are sympathetic or visceral efferent fibers; they are also known as preganglionic fibers of the sympathetic system; the axons of others pass into the anterior and lateral funiculi, where they become longitudinal.

Nerve Cells in the Posterior Column.

     The dorsal nucleus (nucleus dorsalis; column of Clarke) occupies the medial part of the base of the posterior column, and appears on the transverse section as a well-defined oval area. It begins below at the level of the second or third lumbar nerve, and reaches its maximum size opposite the twelfth thoracic nerve. Above the level of the ninth thoracic nerve its size diminishes, and the column ends opposite the last cervical or first thoracic nerve.

Reference:
1. Grey, Henry. 1918. Anatomy of the Human Body; IX Neurology. 3. The Spinal Cord;  22-27
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Laminar Classification

For a better understanding of the laminar and nuclear organisation of grey matter check Sobotta: Atlas of Human Anatomy, Head, Neck, and Neuroanatomy; 2011; p. 335; Fig. 12.183

 

 

Not all the nuclei are presented in this scheme. Use the picture to grasp the concept of laminae.

 

Posterior horns, Laminae I to VI, contain relais neurons for the transmission of afferent sensory input (from skin, propioceptive info, and pain from periphery).

Lateral horns, Lamina VII, contains (nucleus intermediolateralis) neurons for autonomic efferences.

Anterior horns, Laminae VIII to IX, contain the efferent neurons for the muscles.