The brainstem consists of the midbrain, pons and medulla oblongata from above downwards. Superiorly, the brainstem (midbrain) is continuous with the structures forming the forebrain: thalamus, hypothalamus and cerebral hemispheres. Inferiorly, it is continuous with the spinal cord. Posteriorly, the pons and medulla are separated from the cerebellum by the fourth ventricle. The ventricle is continuous below with the central canal, which traverses the lower part of the medulla and becomes continuous with the central canal of the spinal cord. Cranially, the fourth ventricle is continuous with the aqueduct, which passes through the midbrain. The midbrain, pons and medulla are connected to the cerebellum posteriorly by the superior, middle and inferior cerebellar peduncles, respectively . Ten pairs of cranial nerves are attached to the brainstem. The third and fourth nerves emerge from the surface of the midbrain and the fifth from the pons. The sixth, seventh and eighth nerves emerge at the junction of the pons and medulla. The ninth, tenth, cranial part of eleventh and twelfth cranial nerves emerge from the surface of the medulla
Actions of the brain stem..
1.Contains the cranial nerve nuclei from III to XII. Spinal part of accessory extends up to C5 segment of spinal cord. •
2.Contains important reflex centres associated with the control of respiration and cardiovascular system. Pons contains the pneumotaxic and apneustic centre. This influences the dorsal and ventral respiratory groups of medulla. Cardiovascular centre lies in the medulla. • 3.Controls consciousness (ascending reticularactivating system), regulates muscle tone (medial and lateral reticulospinal tracts), controls other vegetative functions inhibits pain