Synonyms
Medical: substantia grisea spinalis CNS, spinal cord, brain, nerve cells
Declaration
According to REXED, the grey spinal cord substance, which is butterfly-shaped in cross-section, can be divided into 10 layers (Laminae spinalales I-X). Layers I-VI form the posterior horn – the rear column (somatosensory = feeling), layers VIII and IX the anterior horn – the front column (motor function = musculature) and layers VII and X form a so-called “intermediate part” (pars intermedia), in which various processes take place.
Classification grey matter
The cells of the gray matter of the spinal cord can be divided into
- Root cells and
- Inland cells
Root cells
The root cells are mostly motor nerve cells (nerve cells that control muscles), which leave the spinal cord via the anterior root: The fibers of the skeletal and visceral muscles still contract in the anterior spinal root, but then separate. The somatomotor root cells (= anterior horn cells, motoneurons) are the largest nerve cells from the spinal cord with a diameter of 40-80 m (i.e. 4-8 hundredths of a mm). They are multipolar ganglion cells, which means that in addition to an impulse-transmitting extension (axon), they have at least two “impulse-receiving” extensions (= dendrites), but usually considerably more.
- Those that supply (innervate) the striated skeletal muscles, that is the muscles that we use at random (for example, when we lift our arm). They are called somatomotor root cells (somatomotor = “body” movement) or alpha-motoneurons (they are located in the anterior horn) and
- Those that supply (innervate) the visceral muscles, which we cannot control on purpose (e.g. the intestinal movements), and glandular cells. They are called visceromotor root cells (lat.
Viscera = the organs, intestines)
- As well as smaller motor root cells called gamma-motoneurons.
- Dendrites
- Cell Body
- Axon
- Nucleus
Many extensions (axons) of other nerve cells end at them in the form of contact points (synapses), which provide information from more distant body locations (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 movement that is meaningful for the organism. Figure Nerve EndingsSynapse
- Nerve ending (Axon)
- Messenger substances, e.g.
dopamine
- Other nerve ending (dendrite)
The visceral root cells are smaller (15-50 m) and belong to the autonomous, i.e. involuntary, nervous system. They are also multipolar. The cell bodies of the sympathicus, which is active during stress reactions, are located in the lateral horn of the thoracic and upper lumbar marrow (C8-L2); their extensions (axons) run briefly with those of the somatomotor anterior horn cells and then, as so-called ramus communicans albus, lead to the border strand of the sympathicus (= truncus sympathicus), which runs alongside the spinal column.
There they are switched to a second nerve cell. The cell bodies of the parasympathicus, which is active at rest, lie in the sacral medulla (S2 to S4) between the anterior and posterior horn. Their extensions lead to ganglia (= accumulations of nerve cells) near their target organs, e.g. the intestine and other organs of the pelvis and lower abdomen, and are switched over there.
