Everything about Mesencephalon totally explained
In biological anatomy, the
mesencephalon (or
midbrain) is the middle of three vesicles that arise from the
neural tube that forms the
brain of developing animals. Caudally the mesencephalon adjoins the
pons (metencephalon) and rostrally it adjoins the
diencephalon (Thalamus, hypothalamus, et al).
In mature human brains, the mesencephalon becomes the least differentiated, from both its developmental form and within its own structure, among the three vesicles. The mesencephalon is considered part of the
brain stem. Its
substantia nigra is closely associated with
motor system pathways of the
basal ganglia.
The human mesencephalon is
archipallian in origin, meaning its general architecture is shared with the most ancient of
vertebrates.
Dopamine produced in the substantia nigra plays a role in motivation and habituation of species from humans to the most elementary animals such as insects.
Corpora Quadrigemina
It consists of four solid optic lobes on the dorsal side of cerebral aqueduct, where the superior anterior pair are called the superior colliculi and the inferior posterior pair is called the inferior colliculi.
The 4 solid optic lobes help to decussate several fibres of the optic nerve. However some fibers also show ipsilateral arrangement (for example they run parallel on the same side without decussating.)
The superior colliculus is involved with saccadic eye movements; while the inferior is a synapsing point for sound information. The
trochlear nerve comes out of the posterior surface of the midbrain, below the inferior colliculus.
Cerebral Peduncle
These are paired structures, present on the ventral side of cerebral aqueduct, and they further carry
tegmentum on the dorsal side and cresta or pes on the ventral side, and both of them accommodate the
corticospinal tract fibres, from the
internal capsule (i.e ascending + descending tracts = longitudinal tract.)
the middle part of cerebral peduncles carry
substantia nigra (also called "Black Matter") which is a type of basal nucleus. It is the only part of the brain that carries melanin pigment.
Between the peduncles is the interpeduncular fossa, which is a cistern filled with
cerebrospinal fluid. The
occulomotor nerve comes out between the peduncles, and the trochlear nerve is visible wrapping around the outside of the peduncles.
Cross-Section Through the Midbrain
The midbrain is usually sectioned at the level of the superior and inferior colliculi.
A cross-section at the level of the superior colliculus shows the
red nucleus, the nuclei of the
oculomotor nerve (and associated
Edinger-Westphal nucleus), as well as the
substantia nigra.
The substantia nigra is still present at inferior colliculus level. Also apparent are the
trochlear nerve nucleus, and the decussation of the superior cerebellar peduncles.
The
cerebral aqueduct runs through the midbrain, and is the communication between the
third and
fourth ventricle.
As a
mnemonic the mesencephalic cross-section resembles a bear (or teddybear) upside down with the two red nuclei as the eyes and the crus cerebri as the ears.
Organization
Additional images
Image:Ventral midbrain.png|Ventral midbrain
Image:midbrainsuperiorcolliculus.png |Diagram of the midbrain, sectioned at the level of the superior colliculus
Image:Gray18.png|Chick embryo of thirty-three hours’ incubation, viewed from the dorsal aspect. X 30.
Image:Gray40.png|Embryo between eighteen and twenty-one days.
Image:Gray711.png|Transverse section of mid-brain at level of inferior colliculi.
Image:Gray712.png|Transverse section of mid-brain at level of superior colliculi.
Image:EmbryonicBrain.svg|Embryonic brain
Image:Human cerebrum lateral view, a part of temporal lobe resected description.JPG|Human cerebrum lateral view
Image:Human brain frontal (coronal) section description.JPG|Human brain frontal (coronal) section
Further Information
Get more info on 'Mesencephalon'.
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