Synonyms
Medical: Substantia alba spinalis CNS, spinal cord, brain, nerve cell, gray matter spinal cord
Introduction
This text tries to present the very complex interrelationships in the spinal cord in an understandable way. Due to the complexity of the topic it is aimed at medical students, doctors and very interested laymen.
Declaration
The Tractus spinobulbaris is divided into the: These two tracts are located in the posterior strand of the white matter of the spinal cord (Funiculus posterior). They lead as an ascending (afferent) tract from the spinal ganglion to two core areas, which lie in the elongated medulla oblongata: the Fasciculus gracilis to the “gracile core”, the Ncl. gracilis, and the Fasciculus cuneatus to the Ncl.
cuneatus. (Ncl. = nucleus = nucleus).
Here lies the first central switch point, the second neuron of the posterior limb. The two pathways are summarized as the tractus spinobulbaris, i.e. “path leading from the spinal cord to the nucleus”, because they conduct the same information, namely the sensation of touch and vibration (the so-called surface or epicritical sensitivity) as well as our feeling for the position of our muscles and joints (and thus of the whole body) in space and also in relation to each other (= sense of position, sense of depth, sense of force or proprioception). The Fasciculus cuneatus conducts the information from the upper half of the body, i.e. it consists of extensions of spinal ganglion cells of the neck and upper chest segments.
The gracilis fascicle directs the information from the lower half of the body, i.e. it consists of extensions of spinal ganglion cells from the lower thoracic, lumbar and sacral segments. The boundary between the two is approximately at the level of breast segment 5 (Th 5), but this is different in each case.
- Fasciculus gracilis (GOLL) and
- Fasciculus cuneatus (BURDACH)
Function
The spinal ganglion cells have their receiving (dendritic) ends wherever they get the “sensitive information”, e.g. :
- In the skin
- In the subcutaneous tissue
- In the joint capsules
- The periosteum
- The cartilage skin
- The muscle fasciae and
- The tendons.
- Dendrites
- Cell Body
- Axon
- Nucleus
These dendritic ends are called “free nerve endings”. Apart from them, there are also specialized receptors such as the so-called Merkel cells of the skin or the Meissen tactile corpuscles, the Golgi tendon organs or the muscle spindles. The stimulus that these endings register, e.g. a stretching stimulus of the tendon, is conducted in a peripheral nerve to the spinal nerve (spinal cord nerve) of a segment and from there to the spinal ganglion cell, which is the first neuron of this pathway.
This neuron is pseudounipolar. The impulse that arrives now travels via the posterior root (radix posterior) into the spinal cord. This is where the signal transmission splits up: But let’s look at the long ascending branch, the actual posterior tract.
Up to their respective nuclei, the gracilis and cuneatus fascicles run on the “same” (= ipsilateral) side, which means that the sensations (touch, vibration, sense of position) from the left foot and left hand also run on the left side of the spinal cord. Both on their path and in the nuclei themselves, there is a strict somatotopic division, which means that each location in the periphery has an exact local representation at all stations of its path up to the cerebral cortex:the further down the segment into which the stimulus information enters, the further sideways in the path it runs. In each of the two nuclei, the fibers are now switched to a second nerve cell, which sends its extensions to the thalamus in the diencephalon.
They are now no longer called “spinobulbaris” because they have left both the spinal cord (spino-) and the nuclei (bulbi) behind. These fibers now each cross over to the other side, i.e. they run contralateral. The fibers that now run on the left side thus conduct the information from the right side of the body.
In this section, they are called Lemniscus medialis, the “loop further in the middle”, and are part of a pathway that leads nerve fibers from various core areas to the thalamus (tractus bulbothalamicus). For this reason, the tract is also referred to as the lemniscale system from here on.In a certain core area of the thalamus (nucleus ventralis posterolateralis), they are switched to their third nerve cell, which sends its extensions to the cerebral cortex, there to the gyrus postcentralis. This is the brain winding, which lies directly behind the central furrow and is, so to speak, a “terminal point” for all sensitive information.
Some fibers of the positional sense, the proprioception, also end in other core areas, especially the nucleus thoracicus dorsalis (also called Stilling-Clarke’s column), which is found in the posterior horn at the level of the segments C8-L3. From there, they are sent to the cerebellar cortex via the posterior cerebellar lateral tract (= tractus spinocerebellaris posterior).
- On the one hand as a long branch in the said (spinobulbar) orbit to the core areas Ncl. gracilis or Ncl. cuneatus (depending on the height at which the stimulus was created),
- On the other hand, as short branches to intermediate neurons (so-called axon collaterals) of the posterior horn or
- Directly to motor cells of the anterior horn, creating a simple reflex path.
