Gray matter spinal cord


Medical: substantia grisea spinalis

CNS, spinal cord, brain, nerve cells

English: spinal cord


The cross-sectionally butterfly-shaped form of the gray spinal cord substance can be divided into 10 layers (Laminae spinales IX) according to REXED.
Here, the layers I-VI form the rear horn / the rear column (somatosensory = feeling), the layers VIII and IX the front horn / the front column (motor system = musculature) and the layers VII and X a so-called. "Intervening part" (Pars intermedia) in which various processing takes place.

Disposition gray matter

The cells of the gray matter of the spinal cord can be divided into:

  • Root cells and
  • within cells

Figure spinal cord

Figure Contents of the spinal canal on a cross section through the cervical spine (section AA)

1st + 2nd spinal cord -
Medulla spinalis

  1. Gray spinal cord substance -
    Substantia grisea
  2. White spinal cord substance -
    Substantia alba
  3. Anterior root - Anterior Radix
  4. Rear root - Radix posterior
  5. Spinal ganglion -
    Ganglion sensorium
  6. Spinal cord nerve - spinal nerve
  7. Periosteum - periosteum
  8. Epidural space -
    Spatium epidural
  9. Hard spinal cord skin -
    Dura mater spinalis
  10. Subdural gap -
    Spatium subdural
  11. Cobweb Skin -
    Arachnoid mater spinalis
  12. Brain water space -
    Spatium subarachnoideum
  13. Spinous process -
    Processus spinosus
  14. Vertebral body
    Foramen vertebrale
  15. Transverse process -
    Processus costiformis
  16. Transverse process hole -
    Foramen transversarium

root cells

The root cells are mostly motor nerve cells (nerve cells that drive muscles), which leave the spinal cord over the anterior root. Here one distinguishes between different types of motor nerve cells:

  1. those that feed (innervate) the striated skeletal muscle, that is the musculature we use arbitrarily (for example, when we lift the arm).
    They are called somatomotor root cells (somatomotor = "body" movement) or alpha motor neurons (they are in the anterior horn) and
  2. those that supply (innervate) the intestinal muscles, which we can not control at will (eg bowel movements), and glandular cells.
    They are called visceromotor root cells (lat. Viscera = the organs, viscera)
  3. and smaller motor root cells called gamma motoneurons.

The fibers of the skeletal and intestinal muscles still contract in the anterior root of the spinal cord, but then separate.

The somatomotor root cells (= front horn cells, motoneurons) are with a diameter of 40-80 m (that is 4-8 hundredths of a millimeter) the largest neurons of the spinal cord.
These are multipolar ganglion cells, which means that they have at least two "impulse-receiving" extensions (= dendrites) in addition to an impulse-transmitting extension (axon), but usually much more.

Figure nerve cell

  1. dendrite
  2. cell body
  3. Axon
  4. nucleus

They are followed by many extensions (axons) of other nerve cells in the form of contact points (synapses), which provide information from distant body parts (periphery), from other spinal cord segments, from the cerebral cortex, from the cerebellum and from the brain stem. This information tells the motor neuron how to react in order to create a meaningful movement for the organism.

Figure nerve endings / synapse

  1. Nerve termination ( axon )
  2. Messenger substances, eg dopamine
  3. other nerve endings ( dentrit )

The visceromotor root cells are smaller (15-50 m) and belong to the autonomous, ie involuntary nervous system. They too are multipolar.
The cell bodies of the sympathetic nervous system active in stress reactions lie in the side horn of the thoracic and upper lumbar cord (C8-L2); their processes (axons) run briefly with those of the somatomotor front horn cells and then, as a so-called ramus communicans albus, they lead to the sympathetic trunk (= truncus sympathicus), which runs alongside the spinal column. There they are switched to a second nerve cell.

The cell bodies of the active at rest parasympathetic located in the sacrum (= sacral) (S2 to S4) between the anterior and posterior horn. Their processes lead to ganglia (= accumulations of nerve cells) in the vicinity of their target organs, such as the intestine and other organs of the pelvis and lower abdomen, and are switched there.

within cells

The internal cells receive nerve impulses from the sensitive nerve cells (neurons) that lie in the dorsal root ganglia and send their processes (axons) into the dorsal horn of the spinal cord. However, with their extensions they remain within the gray matter and convey the incoming information, depending on the cell type, to different other nerve cells. The internal cells can be subdivided into

  • "Short" cells of the spinal cord and its own
  • "Long" strand cells

The cells of the own apparatus connect mostly as so-called. Inter-neurons (interneurons) nerve cells of the spinal cord among themselves.
They are scattered in the gray matter of the spinal cord in different places. The

  • Switching cells connect nerve cells of the spinal cord, which lie on the same side (= ipsilateral) and on the same floor (segment). The
  • Commissural cells connect nerve cells that lie on the other side / opposite side (= contralateral) of the spinal cord, but on the same floor and
  • Association cells connect nerve cells, which are located on the same side but on different levels, ie belonging to different "segments".

By this eigenapparat is guaranteed that on the one hand

  • Not only individual muscle fibers and muscle bundles, but whole muscles and muscle groups are activated to a sensory stimulus, and indeed to another
  • regardless of the wiring in the brain:

For example, if the skin experiences a sting, defensive movements take place through direct connections to the anterior horn cells, which also function when the spinal cord is separated from the brain by a cut.
Through cross-segment communication, all those cells in the anterior horn required for movement of a muscle or muscle group can be reached, and cross-connections between the spinal cord halves also trigger a co-movement on the other side: the reaction is bilateral.
For example, if we stumble with our left foot, reactions still have to be made on both sides of the body to catch the fall.

At this level also works a simple reflex track.

The "long" strand cells are located in the nuclei of the dorsal horn of the spinal cord.
They belong to the afferent, that is, to the ascending, supplying system: the cell bodies receive their information from the spinal ganglion, which is the first switching station (1st neuron) for sensitive information from the inside of the body and from the body surface, and thus form the second switching station ( 2nd neuron) on the way to the brain.
Their processes are long and form thick strands or lanes ascending to the brain. These run in the white matter on each side of the spinal cord front and side, in the so-called front strands and lateral strands.

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