The brainstem

The brainstem ^{[32, 38]} is an anatomical structure of the brain that connects various elements of the nervous system: the cerebrum, cerebellum, and spinal cord. It plays a vital role ^{[32, 41, 46]} due to the essential functions regulated by its nuclei ^[1] , including respiration and heart rate. It is also a transition zone for sensory and motor pathways, as well as a center for pain control ^{[47, 48]}. Furthermore, it serves as the site of emergence ^[41] of the majority of the cranial nerves ^[64].

It is divided into three sections ^[36] , which are, from top to bottom: the midbrain (mesencephalon) ^[49] , the pons ^[181] , and the medulla oblongata ^[72].

The midbrain :

The midbrain (or mesencephalon ^[38] ) is the part of the brainstem directly connected to the brain via the cerebral peduncles ^[38]. Behind these lies the tegmentum ^{[49, 50, 51]} , which contains the aqueduct of Sylvius ^{[41, 43, 72]} ; the latter connects the third ventricle to the fourth ventricle. Posteriorly, the midbrain contains the corpora quadrigemina ^[226] (tectum ^[39] ), which are essential for functions such as vision and hearing.

The Pons :

The pons (or pons Varolii ^[38] ) is the intermediate part of the brainstem. It plays an important role in motor control, particularly as a relay station between the cerebrum and the cerebellum ^[52] ; it also contributes to autonomic functions and facial sensation (it is at this level that the nucleus and the emergence of the trigeminal nerve are located ^[116] ). The pons is connected to the cerebellum by a pair of middle cerebellar peduncles ^[64] and forms the anterior surface (or floor) of the fourth ventricle ^[64].

The medulla oblongata :

The medulla (or myelencephalon ^[38] ) is the part of the brainstem that is continuous with the spinal cord below. It contains the olivary bodies ^[32] as well as the medullary pyramids ^[119] (structures through which the corticospinal fibers ^[39] of the pyramidal tract ^{[179, 227]} pass).

The medulla, or medulla oblongata ^[73] , contains vital autonomic control centers such as the respiratory centers ^[119]. It ends downward at the pyramidal decussation ^{[5, 40]} , a zone where the fibers of the corticospinal tract cross.