Synonym
Metencephalon
Definition
The hindbrain is a part of the central nervous system. It belongs to the brain and is assigned here to the rhombic brain (rhombencephalon), which also includes the medulla oblongata (extended medulla). The Pons (bridge) and the Cerebellum (cerebellum) belong to the hindbrain.
The cerebellum plays a major role in the coordination of movements. The pons is traversed by numerous nerve fibers that run from the brain to peripheral or from peripheral to brain. In addition, some brain nerves have their exit point here.
Bridge
PonsDer Pons borders downward (caudally) on the medulla oblongata and belongs to the brain stem. Cranially, it merges into the midbrain (mesencephalon). The bridge can be divided into two sections, the anterior (ventral) base (pars basilaris pontis) and the posterior (dorsal) hood (tegmentum).
Towards the rear, the pons together with the medulla oblongata form the base of the diamond-shaped pit. Here lies the fourth ventricle, one of several cavities filled with cerebrospinal fluid (liquor) in the area of the brain. The ventral part of the pons can be easily distinguished from the rest of the brain stem, since nerve fibers run transversely here and thus form cross bulges on both sides, which are separated from each other by a notch in the middle.
In this notch runs an important artery for the supply of the rear part of the brain, the arteria basilaris, which results from the confluence of the two arteria vertrebales. Numerous nerve fiber paths run through the pons. Those that run from the cerebral cortex to the periphery, such as the pyramidal tract, one of the most important nerve tracts for voluntary movement, and nerve tracts that run from the periphery into the cerebral cortex, such as the tractus spinothalamicus lateralis.
It is part of the anterior cortex and mainly transmits information about pain and temperature (summarized as protopathic information) from peripheral to central. The pons also contains numerous nerve cell nuclei, the nuclei pontes. Among other things, fibers of the pyramidal tract (corticopontine fibers) coming from the cerebral cortex are switched in them and then transmitted as a kind of copy to the cerebellum (pontocerebellar fibers).
This serves to inform the cerebellum about the movement information that is sent to the muscles of the face, trunk, arms and legs. The cerebellum then plays a decisive role in precise coordination and fine motor skills. A large part of the bridge’s tasks therefore revolves around motor skills.
Further back (dorsally) in the bridge are parts of the reticular format. This is a network of nerve cell nuclei and fibers that runs through the entire brain stem and plays a central role in the regulation of circulation and respiration, among other things. 4 of the 12 brain nerves have their exit point in the area of the bridge.
The 5th cranial nerve, the trigeminal nerve, emerges on both sides of the bridge. It is responsible for the innervation of the masticatory muscles and the sensitivity in the facial area. The cornea is also sensitively innervated by the trigeminal nerve, and is therefore part of the reflex arc during the eyelid closure reflex (corneal reflex).
The sixth cranial nerve, the abducens nerve, is the only cranial nerve that emerges from the rear of the brain stem. It is responsible for supplying one of the six eye muscles. The seventh cranial nerve, the facial nerve, emerges in the cerebellar bridge angle, i.e. in the area between the cerebellum and the bridge.
Among other things, it plays an essential role in facial expression and taste. The eighth cranial nerve, the nervus vestibulocochlearis, also exits at the cerebellar bridge angle; it is essential for hearing and the sense of balance. The pons is damaged in the so-called locked-in syndrome.
The cause is usually a thrombosis, i.e. a blood clot, in the basilar artery. This leads to an infarction in the bridge, the oxygen supply in a part of the pons is permanently interrupted, so this part is functionless. Affected patients are awake and perceive their surroundings unclouded, but they are no longer able to move or speak because the nerve fibers that make this possible run through the pons, which is no longer functional due to the thrombosis. The only communication ability with the outside world for the patients concerned is vertical eye movements.
