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.
The cells of the gray matter of the spinal cord can be divided into:
1st + 2nd spinal cord -
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:
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.
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
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.
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
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
By this eigenapparat is guaranteed that on the one hand
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.