1 The
basic structure of the vertebrate brain
As can be seen in the excellent work "Comparative and Functional Anatomy of
Vertebrates" by Hildebrand/Goslow [11] from page 361 onwards, the brain develops
from the front section of the neural tube. This tube forms three primary
vesicles by constriction, which are
-
Forebrain (Prosencephalon)
-
midbrain (mesencephalon) and
-
Diamond brain (rhombencephalon)
can be designated. In the following stage, additional constrictions divide the
brain into five vesicles. This divides the forebrain (prosencephalon) into the
final brain (telencephalon) and the diencephalon. The rhombic brain is divided
into the hindbrain (metencephalon) and the extended medulla (myelencephalon,
medulla oblongata). The midbrain remains undivided. Thus there are five regions
in the brain:
-
endbrain (telencephalon)
-
Interbrain (diencephalon)
-
Midbrain (Mesencephalon)
-
Hindbrain (Metencephalon)
-
elongated medulla
(myelencephalon, medulla oblongata).
The midbrain, the isthmic region and the medulla oblongata are also called the
brain stem.
Since vertebrates are bilateria, i.e. have a bilaterally symmetrical body, the
brain and spinal cord are also
partly bilaterally symmetrical. Therefore, many of its substructures are
duplicated.
It is only possible to rationally analyse signal processing in a system as
highly complex as the vertebrate nervous system if at least the most
important of its basic structures are known. Therefore, the most important
subsystems of the vertebrate brain are listed below. If necessary, the
reader may deal with the basic structure of the vertebral column himself.
The following information was taken from the work "Wie einzigartig ist der
Mensch" [48] by Gerhard Roth, Spektrum Akademischer Verlag, 2011, from page
169 as well as from the work "Vergleichende und funktionelle Anatomie der
Wirbeltiere" by Hildebrand/Goslow, Springer Verlag, from page 362. Anyone
interested in brain research should therefore have this basic knowledge.
1.1 The substructures of the
medulla oblongata of vertebrates
-
The medulla oblongata connects to the spinal cord
and is therefore also called the elongated medulla.
-
It is the origin of all motor nerves
-
It is the target area for the sensory brain nerves III to XII
Oculomotor nerve (eye muscle nerve)
-
Trochlear nerve (also eye muscle nerve)
-
Trigeminal nerve (facial nerve)
-
Abducens nerve (another eye muscle nerve)
-
Facial nerve
-
Nervus stato-acusticus (balance and auditory nerve)
-
Nervus glossopharyngeus (lingual nerve)
-
Vagus nerve (vagus nerve)
-
Accessorius nerve (accessory nerve)
-
Hypoglossal nerve
-
It contains primary and secondary switching and processing points of
somatosensory and viscerosensory (coming from the intestines) information
-
It is the starting point for the motor parts of the fifth to seventh and ninth
to twelfth cranial nerve
-
It contains networks and centres for the control of vital functions such as
respiration and circulation as well as for alertness and attention
-
It is a convergence zone of numerous descending nerve tracts from all parts of
the brain
-
Although the reticular formation, which is important for cognitive functions,
is part of the rostral medulla oblongata, it continues to the tegmentum of the
midbrain.
-
The median zone of the Formatio reticularis contains the raphe seeds, which
produce the neurotransmitter serotonin. On the one hand they supply almost all
limbic centres with serotonin, on the other hand their descending fibres
project towards the spinal cord.
-
The lateral zone of the reticular format contains the locus caeruleus, whose
neurons produce norepinephrine and project it into many limbic and associative
centers of the brain.
-
The medulla oblongata has a very conservative basic structure, which has been
identical in principle in all vertebrates since the earliest history of
evolution. Nevertheless, there have been individual and sometimes spectacular
variations in specific vertebrate species (see Roth, above work, page 175).
-
The medulla oblongata also contains the olive pit complex, i.e. the nucleus
olivaris principalis, the nucleus olivaris accessorius medialis and the
nucleus olivaris accessorius posterior (secondary olives)
-
In the dorsal section of the medulla oblongata, the tegmentum, lie the cranial
nerve nuclei into which the various cranial nerves enter.
-
Ascending and descending pathways of various substructures run through the
medulla oblongata, such as the pyramidal path from the motor cortex to the
spinal cord.
-
The medulla oblongata can also include the pons (the bridge). The pons itself
is subdivided into the foot of the bridge (pars basalis pontis) and the bridge
cap (tegmentum pontis).
-
The descending fibres of the pyramid tract, which comes from the cortex and
goes to the spinal cord, pass through the foot of the bridge.
Also in the foot of the bridge are the bridge nuclei (Ncll. pontis), which
receive input from the cortex and project it to the cerebellar nuclei.
-
The structure of the medulla oblongata is symmetrical, one half is responsible
for each half of the body, with some projection paths alternating between the
two sides.