The metencephalon is generally considered a part of the brain that largely consists of the brain's cerebellum and pons. Comprising such structures of the center of the nervous system means that the metencephalon contributes to brain's various functions. It is usually classified as one of the two parts of the developing rhombencephalon, or hindbrain, with the other part being the myelencephalon.
Specifically, the metencephalon is considered part of the central nervous system (CNS), which receives and processes data for regulating the activity of the parts of the body. This is because it is one of the components of the brain, which, along with the spinal cord and other components, comprises most of the nervous system. Also, the CNS is partly named after the brain, which is the center of the entire nervous system.
It is during embryonic development that the metencephalon began to take shape. By five weeks of embryonic development, the rhombencephalon — appearing as a tiny intracellular membrane-covered sac called a vesicle — splits into two. The metencephalon serves as the primary vesicle, while the myelencephalon, placed behind it, serves as the secondary one. The metencephalon develops its two main defining structures by the end of the third month.
These main defining structures are the cerebellum and the pons. The cerebellum, named after the Latin term for "little brain" is in the part of the brain that is commonly associated with the body's movement by receiving signals from other parts of the nervous system. The cerebellum is connected to the pons, which is appropriately named after the Latin term for "bridge." About 0.98 inches (2.5 cm) in length, the pons constitutes the upper part of the brain stem. The metacephalon in particular contributes to functions like sleep and dreaming, muscle tone maintenance, balance, arousal, cardiac reflexes and circulation.
There are other parts of the metencephalon as well. The structure holds a part of one of the brain's four fluid-filled cavities called the fourth ventricle. It also contains a portion of the fifth, sixth, seventh and eighth cranial nerves. These nerves are referred to the trigeminal, abducens, facial and vestibulocochlear nerves.
In terms of location, the metencephalon is situated below the rear portion of the cerebrum and above the medulla oblongata. The cerebrum, also known as the telencephalon, forms part of the forebrain, with the diencephalon being the other component. The medulla oblongata constitutes the lower part of the brain stem, placed below the pons.
