Vertebrate brain theory

ISBN 978-3-00-064888-5

Monograph of Dr. rer. nat. Andreas Heinrich Malczan

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.

Monograph of Dr. rer. nat. Andreas Heinrich Malczan