Spinal cord gray matter
Medical: substantia grisea spinalis
CNS, spinal cord, brain, nerve cells
English: spinal cord
The shape of the gray spinal cord substance, which is butterfly-shaped in cross-section, can be divided into 10 layers (laminae spinales I-X) according to REXED.
Layers I-VI form the posterior horn / the back pillar (somatosensory = feeling), the layers VIII and IX the front horn / the front pillar (motor skills = muscles) and the layers VII and X form a so-called "intermediate part" (pars intermedia) , in which various processing takes place.
Classification of gray matter
The cells of the gray matter of the spinal cord can be divided into:
- Root cells and
- Internal cells
Figure spinal cord
1st + 2nd spinal cord -
- Gray matter of the spinal cord -
- White spinal cord substance -
- Anterior root - Radix anterior
- Back root - Radix posterior
- Spinal ganglion -
- Spinal nerve - N. spinalis
- Periosteum - Periosteum
- Epidural space -
- Hard spinal cord skin -
Dura mater spinalis
- Subdural gap -
- Cobweb skin -
Arachnoid mater spinalis
- Cerebral water space -
- Spinous process -
- Vertebral bodies -
- Transverse process -
- Transverse process hole -
You can find an overview of all Dr-Gumpert images at: medical illustrations
The Root cells are mostly motor nerve cells (nerve cells that control muscles) that leave the spinal cord via the anterior root.A distinction is made between different types of motor nerve cells:
- those who the striated Skeletal muscles supply (innervate), these are the muscles that we use arbitrarily (for example when we raise our arm).
They are called somatomotor root cells (somatomotor = "body" movement) or alpha motor neurons (they are located in the anterior horn) and
- those that supply (innervate) the intestinal muscles that we cannot control voluntarily (e.g. the bowel movements), as well as gland cells.
They are called visceromotor root cells (Latin Viscera = organs, intestines)
- as well as smaller motor root cells called gamma motor neurons.
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, motor neurons) are the largest nerve cells in the spinal cord with a diameter of 40-80 m (that's 4-8 hundredths of a mm).
There are multipolar ganglion cells, which means that apart from an impulse-transmitting continuation (Axon) at least two "impulse-receiving" extensions (= Dendrites), but usually much more.
Figure nerve cell
- Cell body
- Cell nucleus
Many projections (axons) of other nerve cells in the form of contact points (Synapses), the information from more distant parts of the body (periphery), from other spinal cord segments, from the Cerebral cortex, from the Cerebellum and from the Brain stem deliver. This information tells the motor neuron how to react in order to create a movement that is meaningful for the organism.
Figure nerve endings / synapse
- Nerve ending (Axon)
- Messenger substances, e.g. Dopamine
- other nerve endings (Dendrite)
The visceromotor root cells are smaller (15-50 m) and belong to the autonomous, so involuntary nervous system. They are also multipolar.
The cell bodies of the active in stress reactions Sympathetic lie in the lateral horn of the thoracic and upper lumbar cords (C8-L2); their appendages (Axons) run briefly with those of the somatomotor anterior horn cells and then lead as so-called ramus communicans albus to the Sympathetic trunk (= Sympathetic trunk), next to the Spine runs. There they are on a second Nerve cell switched.
The cell bodies of the active at rest Parasympathetic nervous system lie in the sacrum (= sacral) medulla (S2 to S4) between anterior and posterior horn. Their processes lead to Ganglia (= Accumulations of nerve cells) in the vicinity of their target organs, e.g. of the intestines 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 are in the Spinal ganglia lie and their appendages (Axons) in the Back horn of the spinal cord. However, their appendages remain within the gray matter and, depending on the cell type, transmit the incoming information to various other nerve cells. The inner cells can be subdivided into
- "Short" cells of the self-apparatus of the spinal cord and
- "Long" cord cells
The Self-apparatus cells For the most part, as so-called inter-neurons (interneurons) connect nerve cells of the spinal cord with one another.
They are scattered in the gray matter of the spinal cord in different places. The
- Switching cells connect nerve cells of the spinal cord that are on the same side (= ipsilateral) and on the same floor (segment). The
- Commissure cells connect nerve cells that are on the other side / opposite side (= contralateral) of the spinal cord, but on the same floor
- Association cells connect nerve cells that are on the same side, but on different floors, that is, belong to different “segments”.
This own telephone ensures that on the one hand
- not only individual muscle fibers and muscle bundles, but entire muscles and muscle groups are activated in response to a sensitive stimulus, and to the other
- regardless of the circuitry in the brain:
Does the skin experience e.g. a sting, defensive movements take place due to the direct connections to the anterior horn cells, which still function when the spinal cord is separated from the brain by a cut.
Through cross-segment communication, all those cells in the anterior horn can be reached that are needed to move a muscle or muscle group, and the cross connections between the halves of the spinal cord also trigger a movement in the same direction on the other side: the reaction is bilateral.
For example, if we stumble with our left foot, reactions must still take place on both sides of the body in order to intercept the fall.
A simple one also works at this level Reflex path.
The lengths" Cord cells lie in the nuclei of the dorsal horn of the spinal cord.
They belong to afferents, that means to the ascending, supplying system: The cell bodies receive their information from the Spinal ganglion, which represents the first switching station (1st neuron) for sensitive information from inside the body and from the body surface, and thus form the second switching station (2nd neuron) on the way to the brain.
Their appendages are long and form thick strands or webs that ascend to the brain. These run in the white matter on each side of the spinal cord in the front and side, in the so-called Front strands and Side strands.