How is the brain stem separated and what is it’s functions of each part

Together, they help to regulate breathing, heart rate, blood pressure, and several other important functions. All of these brainstem functions are enabled because of its unique anatomy; since the brainstem houses cranial nerve nuclei and is a passageway for many important neural pathways.

Medulla oblongata
Basilar portion - contains the pyramids (transmit the corticospinal tracts), olives (transmit the olivocerebellar tract)
Medullary tegmentum - contains the gracile and cuneate tubercles (and tracts), four cranial nerve nuclei

Pons
Basilar portion - accommodates the basilar artery, corticospinal tract, corticonuclear fibers, pontine nuclei
Pontine tegmentum - contains the pontine reticular formation, four cranial nerve nuclei, ascending spinal tracts, loci coerulei

Midbrain
Traversed by the cerebral aqueduct
Contains the quadrigeminal plate (superior and inferior colliculi)
Cerebral peduncles separated into crura cerebri and tegmentum
Tectum – posterior to the cerebral aqueduct

Ventricles and cisterns
Fourth ventricle and the foramina of Luschka and Magendie
Interpeduncular, Quadrigeminal, Pontine, and Cerebellomedullary cisterns

Function
Regulate breathing, heart rate, blood pressure, consciousness, audio-visual reflexes, taste and digestion, autonomic regulation, balance and coordination