Introduction to the Brain Stem
The brainstem is located at the rostral end of the spinal cord and extends superiorly to the base of the thalamus (forebrain). The bulbous enlargements that form the brainstem reflects its origin from the caudal two cephalic vesicles of the embryo, the mesencephalon and the rhombencephalon. The expansion in size, characteristic of the brainstem, over the diameter of the spinal cord reflects the fact that former structures contains the neuronal circuitry required to regulate body homeostasis, such as cardiorespiratory system regulation and that necessary to control the complicated musculature of the orofacial and pharyngeal-laryngeal regions.
A sagittal section of the brainstem illustrating it main divisions. Note the greatly expanded diameter of the brainstem over the spinal cord. The pons is the largest expansion of the brainstem.
the major divisions of the brainstem are the medulla, pons and midbrain, although some authorities will also include the hypothalamus as the rostralmost extend of this structure. Developmentally and functionally the thalamus is part of the forebrain.