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Diagram depicting the main subdivisions of the embryonic vertebrate brain These regions will later differentiate into Forebrain , Midbrain and Hindbrain structures
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Diagram of the midbrain, sectioned at the level of the Superior Colliculus
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Mesencephalon
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In biological anatomy, the (or '''midbrain''') is the middle of three vesicles that arise from the
Neural Tube that forms the
Brain of developing animals. The mesencephalon caudally adjoins the
Pons and rostrally adjoins the
Diencephalon .
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 or the
Midbrain . The
Substantia Nigra is closely associated with
Motor System pathways of the
Basal Ganglia .
The mesencephalon is
Archipallian in origin, meaning its general architecture is shared with the most ancient of
Vertebrate s.
Dopamine produced in the subtantia nigra plays a role in motivation and habituation of species from humans to the most elementary animals such as insects.
On the posterior (back) surface, there are structures called the superior colliculus and the inferior colliculus. The superior colliculus is involved with saccadic eye movements, 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.
On the anterior surface the
Cerebral Peduncle s are prominent. These contain the
Corticospinal Tract fibres, from the
Internal Capsule , as well as the
Substantia Nigra .
Between the peduncles is the interpeduncular fossa, which is a cistern filled with
Cerebrospinal Fluid . The
Oculomotor Nerve comes out between the peduncles, and the trochlear nerve is visible wrapping around the outside of the peduncles.
section through mid-brain.
1.
Corpora Quadrigemina .
2.
Cerebral Aqueduct .
3.
Central Gray Stratum .
4.
Interpeduncular Space .
5.
Sulcus Lateralis .
6.
Substantia Nigra .
7.
Red Nucleus of
Tegmentum .
8.
Oculomotor Nerve , with 8’, its nucleus of origin.
a.
Lemniscus (in blue) with a’ the
Medial Lemniscus and a" the
Lateral Lemniscus .
b.
Medial Longitudinal Fasciculus .
c.
Raphé .
d.
Temporopontine Fibers .
e. Portion of
Medial Lemniscus , which runs to the
Lentiform Nucleus and
Insula .
f.
Cerebrospinal Fibers .
g.
Frontopontine Fibers .]]
The midbrain is usually sectioned at the level of the superior and inferior colliculi.
A cross-section through 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.
