The metencephalon is the

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

nic part of the

hindbrain The hindbrain or rhombencephalon or lower brain is a developmental categorization of portions of the central nervous system in vertebrates. It includes the medulla, pons, and cerebellum. Together they support vital bodily processes. Metencephal ...

that differentiates into the

pons The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Va ...

and the

cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebe ...

. It contains a portion of the

fourth ventricle The fourth ventricle is one of the four connected fluid-filled cavities within the human brain. These cavities, known collectively as the ventricular system, consist of the left and right lateral ventricles, the third ventricle, and the fourth ve ...

and the

trigeminal nerve In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and che ...

(CN V),

abducens nerve The abducens nerve or abducent nerve, also known as the sixth cranial nerve, cranial nerve VI, or simply CN VI, is a cranial nerve in humans and various other animals that controls the movement of the lateral rectus muscle, one of the extraocu ...

(CN VI),

facial nerve The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste ...

(CN VII), and a portion of the vestibulocochlear nerve (CN VIII).

Embryology

The metencephalon develops from the higher/rostral half of the embryonic

rhombencephalon The hindbrain or rhombencephalon or lower brain is a developmental categorization of portions of the central nervous system in vertebrates. It includes the medulla, pons, and cerebellum. Together they support vital bodily processes. Metencephal ...

, and is differentiated from the myelencephalon in the embryo by approximately 5 weeks of age. By the third month, the metencephalon differentiates into its two main structures, the pons and the cerebellum.

Functions

The pons regulates breathing through particular nuclei that regulate the breathing center of the

medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (invol ...

. The

works to coordinate muscle movements, maintain posture, and integrate sensory information from the

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in th ...

and proprioceptors in the muscles and joints.

Development

At the early stages of brain development, the brain vesicles that are formed are imperative.Nakamura, H., and Watanabe, Y. Isthmus organizer and regionalization of the mesencephalon and metencephalon. Int. J. Dev. Biol. 49: 231-235 (2005). doi: 10.1387/ijdb.041964hn. Each brain region is characterized by its own specific architecture. These regions of the brain are determined by a combination of transcription factors and the signals that change their expression. The

isthmus An isthmus (; ; ) is a narrow piece of land connecting two larger areas across an expanse of water by which they are otherwise separated. A tombolo is an isthmus that consists of a spit or bar, and a strait is the sea counterpart of an isthmus ...

is the main organizing center for the tectum and the cerebellum.Matsunaga, E., Katahira, T., and Nakamura, H
"Role of Lmx1b and Wnt1 in mesencephalon and metencephalon development"
Development" (2002) The tectum is the dorsal part of the metencephalon. The tectum includes the superior and inferior colliculli, which play a part in visual and audio processing. Two of the major genes that affect the metencephalon are Fgf8 and Wnt1, which are both expressed around the isthmus. Fgf8 is also known as Fibroblast Growth Factor 8. It is a protein that is widely thought to be the most important organizing signal. Its main function is to set up and maintain the barrier between the midbrain and hindbrain, specifically between the mesencephalon and metencephalon. It also plays a large role in deciding the structure of the mid- and hindbrain. Wnt1 is a proto-oncogene protein (Wingless-type MMTV integration site family, member 1). This gene was originally thought to play a role in the development of the midbrain and hindbrain, but studies have shown that this may not be the case. Wnt1 is thought to be behind the genetic disorder called Joubert Syndrome, a disorder that affects the cerebellum. Otx1 and Otx2 are genes that play important parts in the development of the brain, and studies have shown that their roles change throughout the brain’s development.Sakuri, Y., Kurokawa, D., Kiyonari, H., Kajikawa, E., Suda, Y., and Aizawa, S
"Otx2 and Otx1 protect diencephalon and mesencephalon from caudalization into metencephalon during early brain regionalization"
"Developmental Biology" (2010). It is thought that at the stage of brain development wherein the rostral brain is regionalized into its different parts (telencephalon, diencephalon, metencephalon, and mesencephalon) that Otx2 and Otx1 protect the caudalization of the diencephalon and mesencephalon into metencephalon. Pons - Middle

References

{{Authority control Brainstem Central nervous system Cranial nerves Animal developmental biology

Embryology

Functions

Development

See also

References