The rhombencephalon is a structure in the brain composed of the medulla oblongata and hindbrain. Its functions include the control of various reflexes, the regulation of vomiting, respiration, and blood circulation, and motor processes. Diseases and disorders affect the various functional centers and can result from lesions, neurological diseases, and specifically rhombencephalosynapsis.
What is the rhombencephalon?
The rhombencephalon is a part of the brain and is also known by the trivial name “diamond brain.” Both the medulla oblongata (extended spinal cord) and the hindbrain (metencephalon), or 4th cerebral vesicle, belong to this part of the central nervous system. The rhombencephalon maintains close connections to the spinal cord and cerebrum as well as to the cerebral ventricles. These cavities lie within the brain tissue and contain fluid (cerebrospinal fluid); medicine therefore also groups the ventricles together as the internal cerebrospinal fluid space. In addition, the rhombencephalon is connected to the outer cerebrospinal fluid space, which is located between two meninges (arachnoid mater and pia mater). The name of the rhombencephalon comes from the rhomboid fossa, which is located at the pons.
Anatomy and structure
Within the rhombencephalon, physicians distinguish two major anatomical structures: the medulla oblongata (medulla oblongata) and the hindbrain (metencephalon). The medulla oblongata is not sharply distinct from the spinal cord; this is true both for its anatomy and for its functions, which closely resemble those of the spinal cord. Complex neuronal networks in the medulla oblongata form functional centers such as the vomiting and respiratory centers. Macroscopically, however, they are hardly distinguishable from the rest of the tissue. However, various nuclei are easily recognizable, as well as the central canal, which projects downward from the medulla oblongata like a tube. The central canal is derived from the neural tube. The metencephalon or hindbrain, which is also part of the rhombencephalon, consists of the cerebellum (cerebellum) and bridge (pons). The cerebellum has its own cortex with three layers; specific types of neurons occur in each layer. Beneath the cortex, in the interior or medulla of the cerebellum, is predominantly white matter. This consists of the isolated axons of the neurons and is important for circuitry and information processing. Nuclei in the medulla of the cerebellum each form demarcated structures with specific tasks. The pons, the other part of the metencephalon, also contains nuclei – including the nucleus motorius nervi trigemini, the nucleus nervi abducentis, and the nucleus motorius nervi facialis. Nerve tracts traverse the pons and connect the brain to the rest of the human body.
Function and tasks
The various parts of the rhombencephalon each perform their own tasks; in summary, the main task of the rhombencephalon is the control of involuntary motor processes. The medulla oblongata connects the spinal cord to other parts of the rhombencephalon and relays nerve signals to and from most regions of the body. Functional networks of neurons in the medulla oblongata form the respiratory center, which controls all involuntary modes of respiration, and the vomiting center, which initiates the vomiting act in response to signals from the digestive tract, the vestibular organ, or the chemical receptors of the area postrema. Furthermore, the medulla oblongata is home to circuitry for reflexes to gag, cough, sneeze, swallow, and suck (in infants). The function of the pons is predominantly to transmit information. The motor nerve nuclei of the bridge form a site of origin of cranial nerves. The functions of the cerebellum are particularly extensive, housing half of all neurons in the brain. The tasks of the cerebellum range from motor processes to learning processes to contributions to higher cognitive functions. The cerebrocerebellum is primarily responsible for the latter; the rhombencephalon participates in the pre-planning of movements in this way. The motor control of the cerebellum contributes to speech and coordinates postural and supporting motor functions as well as movements during walking and standing.
Diseases
Rhombencephalosynapsis is a very specific clinical picture of the rhombencephalon; the disease occurs rarely. The basis is a malformation in the cerebellum.In a healthy person, this part of the rhombencephalon consists of two halves, but in rhombencephalosynapsis they are fused together. This condition affects the various anatomical and functional structures of the cerebellum. Patients are often mentally disabled and suffer from a number of characteristic disorders. One of these is ataxia, which is a disorder of movement coordination. As gait ataxia, it may also be a consequence of lesions in the rhombencephalon and other brain areas; affected individuals are unable to coordinate movements correctly despite the absence of muscular restrictions. In addition to walking, sitting and/or standing may also be impaired. Other movement disorders such as dyskinesia may also occur as a result of rhombencephalosynapsis; in this case, the brain is unable to adequately execute the sequence of movement, resulting in abnormalities in walking or other muscular activities. The ability to speak is also impaired in some cases (dysarthria), although this need not be accompanied by comprehension problems. Affected individuals may squint (strabismus) or suffer from neurally induced seizures (epilepsy), which can lead to further limitations and consequential damage. The symptoms of rhombencephalosynapsis and the extent to which they manifest themselves depend on the type and extent of the malformation in the cerebellum. Physicians can treat rhombencephalosynapsis symptomatically to some extent, for example, with anticonvulsants or antiepileptic drugs to prevent seizures.
