During embryonic development, the medulla oblongata develops from themyelencephalon. The myelencephalon is a secondarybrain vesicle which forms during the maturation of therhombencephalon, also referred to as the hindbrain.
Thebulb is an archaic term for the medulla oblongata.[1] In modern clinical usage, the wordbulbar (as inbulbar palsy) is retained for terms that relate to the medulla oblongata, particularly in reference tomedical conditions. The word bulbar can refer to thenerves andtracts connected to the medulla such as thecorticobulbar tract, and also by association to thosemusclesinnervated, including those of thetongue,pharynx andlarynx.
Theanterior median fissure contains a fold ofpia mater, and extends along the length of the medulla oblongata. It ends at the lower border of thepons in a small triangular area, termed theforamen cecum. On either side of this fissure are raised areas termed themedullary pyramids. The pyramids house thepyramidal tracts–thecorticospinal tract, and thecorticobulbar tract of the nervous system. At the caudal part of the medulla these tracts cross over in thedecussation of the pyramids obscuring the fissure at this point. Some other fibers that originate from the anterior median fissure above the decussation of the pyramids and run laterally across the surface of the pons are known as theanterior external arcuate fibers.
Just above the tubercles, the posterior aspect of the medulla is occupied by a triangular fossa, which forms the lower part of the floor of thefourth ventricle. The fossa is bounded on either side by theinferior cerebellar peduncle, which connects the medulla to thecerebellum.
The lower part of the medulla, immediately lateral to the cuneate fasciculus, is marked by another longitudinal elevation known as thetuberculum cinereum. It is caused by an underlying collection of gray matter known as thespinal trigeminal nucleus. The gray matter of this nucleus is covered by a layer of nerve fibers that form the spinal tract of thetrigeminal nerve. The base of the medulla is defined by thecommissural fibers, crossing over from the ipsilateral side in the spinal cord to the contralateral side in the brain stem; below this is the spinal cord.
Posterior inferior cerebellar artery: This is a major branch of the vertebral artery, and supplies the posterolateral part of the medulla, where the main sensory tracts run andsynapse. It also supplies part of the cerebellum.
Direct branches of thevertebral artery: The vertebral artery supplies an area between the anterior spinal and posterior inferior cerebellar arteries, including thesolitary nucleus and other sensory nuclei and fibers.
The medulla oblongata connects the higher levels of thebrain to thespinal cord, and is responsible for several functions of theautonomous nervous system which include:
Reflex centers of vomiting, coughing, sneezing and swallowing. These reflexes which include thepharyngeal reflex, theswallowing reflex (also known as the palatal reflex), and themasseter reflex can be termedbulbar reflexes.[5]
BothLamprey andHagfish possess a fully developed medulla oblongata.[6][7] Since these are both very similar to earlyagnathans, it has been suggested that the medulla evolved in these early fish, approximately 505 million years ago.[8] The status of the medulla as part of the primordialreptilian brain is confirmed by its disproportionate size in modernreptiles such as thecrocodile,alligator, andmonitor lizard.
Diagram showing the positions of the three principal subarachnoid cisternæ.
Micrograph of the posterior portion of theopen part of the medulla oblongata, showing thefourth ventricle (top of image) and the nuclei of CN XII (medial) and CN X (lateral).H&E-LFB stain.
