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Midbrain
The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated
with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature
regulation.[2] The name comes from the Greek mesos, "middle", and enkephalos, "brain".[3]

2. Midbrain
Figure shows the midbrain (A) and surrounding regions; sagittal view of one cerebellar hemisphere. B:
Pons. C: Medulla. D: Spinal cord. E: Fourth ventricle. F: Arbor vitae. G: Nodule. H: Tonsil. I: Posterior lobe.
J: Anterior lobe. K: Inferior colliculus. L: Superior colliculus.
Inferior view in which the midbrain is encircled blue.
Details
Pronunciation UK: /ˌmɛsɛnˈsɛfəlɒn, -kɛf-/, US: /ˌmɛzənˈsɛfələn/;[1]
Part of Brainstem
Identifiers
Latin mesencephalon
MeSH D008636 (https://meshb.nlm.nih.gov/record/ui?ui
=D008636)
NeuroNames 462 (http://braininfo.rprc.washington.edu/centrald

3. The principal regions of the midbrain are the tectum, the cerebral aqueduct, tegmentum, and the
cerebral peduncles. Rostrally the midbrain adjoins the diencephalon (thalamus, hypothalamus,
etc.), while caudally it adjoins the hindbrain (pons, medulla and cerebellum).[4]
In the rostral
direction, the midbrain noticeably splays laterally.
irectory.aspx?ID=462)
NeuroLex ID birnlex_1667 (http://www.neurolex.org/wiki/birnlex
_1667)
TA98 A14.1.03.005 (http://www.unifr.ch/ifaa/Public/Entr
yPage/TA98%20Tree/Entity%20TA98%20EN/14.1.
03.005%20Entity%20TA98%20EN.htm)
TA2 5874 (https://ta2viewer.openanatomy.org/?id=587
4)
FMA 61993 (https://bioportal.bioontology.org/ontologie
s/FMA/?p=classes&conceptid=http%3A%2F%2Fpu
rl.org%2Fsig%2Font%2Ffma%2Ffma61993)
Anatomical terms of neuroanatomy
Structure
Brainstem (dorsal view).
A:Thalamus B:Midbrain C:Pons
D:Medulla oblongata
7 and 8 are the colliculi.

4. Sectioning of the midbrain is usually performed axially, at one of two levels – that of the superior
colliculi, or that of the inferior colliculi. One common technique for remembering the structures
of the midbrain involves visualizing these cross-sections (especially at the level of the superior
colliculi) as the upside-down face of a bear, with the cerebral peduncles forming the ears, the
cerebral aqueduct the mouth, and the tectum the chin; prominent features of the tegmentum
form the eyes and certain sculptural shadows of the face.
Tectum
The tectum (Latin for roof) is the dorsal side of the midbrain. The position of the tectum is
contrasted with the tegmentum, which refers to the region in front of the ventricular system, or
floor of the midbrain.
It is involved in certain reflexes in response to visual or auditory stimuli. The reticulospinal tract,
which exerts some control over alertness, takes input from the tectum,[5] and travels both
rostrally and caudally from it.
The corpora quadrigemina are four mounds, called colliculi, in two pairs – a superior and an
inferior pair, on the surface of the tectum. The superior colliculi process some visual
information, aid the decussation of several fibres of the optic nerve (some fibres remain
ipsilateral), and are involved with saccadic eye movements. The tectospinal tract connects the
superior colliculi to the cervical nerves of the neck, and co-ordinates head and eye movements.
Each superior colliculus also sends information to the corresponding lateral geniculate nucleus,
…
Principal connections of the tectum

5. with which it is directly connected. The homologous structure to the superior colliculus in non
mammalian vertebrates including fish and amphibians, is called the optic tectum; in those
animals, the optic tectum integrates sensory information from the eyes and certain auditory
reflexes.[6][7]
The inferior colliculi – located just above the trochlear nerve – process certain auditory
information. Each inferior colliculus sends information to the corresponding medial geniculate
nucleus, with which it is directly connected.
Cerebral aqueduct
The cerebral aqueduct is the part of the ventricular system which links the third ventricle
(rostrally) with the fourth ventricle (caudally); as such it is responsible for continuing the
circulation of cerebrospinal fluid. The cerebral aqueduct is a narrow channel located between
the tectum and the tegmentum, and is surrounded by the periaqueductal grey,[8] which has a role
in analgesia, quiescence, and bonding. The dorsal raphe nucleus (which releases serotonin in
response to certain neural activity) is located at the ventral side of the periaqueductal grey, at the
level of the inferior colliculus.
The nuclei of two pairs of cranial nerves are similarly located at the ventral side of the
periaqueductal grey – the pair of oculomotor nuclei (which control the eyelid, and most eye
movements) is located at the level of the superior colliculus,[9] while the pair of trochlear nuclei
…
Ventricular system anatomy showing the cerebral aqueduct, labelled centre right.

6. (which helps focus vision on more proximal objects) is located caudally to that, at the level of
the inferior colliculus, immediately lateral to the dorsal raphe nucleus.[8] The oculomotor nerve
emerges from the nucleus by traversing the ventral width of the tegmentum, while the trochlear
nerve emerges via the tectum, just below the inferior colliculus itself; the trochlear is the only
cranial nerve to exit the brainstem dorsally. The Edinger-Westphal nucleus (which controls the
shape of the lens and size of the pupil) is located between the oculomotor nucleus and the
cerebral aqueduct.[8]
Tegmentum
The midbrain tegmentum is the portion of the midbrain ventral to the cerebral aqueduct, and is
much larger in size than the tectum. It communicates with the cerebellum by the superior
…
Cross-section of the midbrain at the level of the superior colliculus
Cross-section of the midbrain at the level of the inferior colliculus.

7. cerebellar peduncles, which enter at the caudal end, medially, on the ventral side; the cerebellar
peduncles are distinctive at the level of the inferior colliculus, where they decussate, but they
dissipate more rostrally.[8] Between these peduncles, on the ventral side, is the median raphe
nucleus, which is involved in memory consolidation.
The main bulk of the tegmentum contains a complex synaptic network of neurons, primarily
involved in homeostasis and reflex actions. It includes portions of the reticular formation. A
number of distinct nerve tracts between other parts of the brain pass through it. The medial
lemniscus – a narrow ribbon of fibres – passes through in a relatively constant axial position; at
the level of the inferior colliculus it is near the lateral edge, on the ventral side, and retains a
similar position rostrally (due to widening of the tegmentum towards the rostral end, the position
can appears more medial). The spinothalamic tract – another ribbon-like region of fibres – are
located at the lateral edge of the tegmentum; at the level of the inferior colliculus it is
immediately dorsal to the medial lemiscus, but due to the rostral widening of the tegmentum, is
lateral of the medial lemiscus at the level of the superior colliculus.
A prominent pair of round, reddish, regions – the red nuclei (which have a role in motor co-
ordination) – are located in the rostral portion of the midbrain, somewhat medially, at the level of
the superior colliculus.[8]
The rubrospinal tract emerges from the red nucleus and descends
caudally, primarily heading to the cervical portion of the spine, to implement the red nuclei's
decisions. The area between the red nuclei, on the ventral side – known as the ventral tegmental
area – is the largest dopamine-producing area in the brain, and is heavily involved in the neural
reward system. The ventral tegmental area is in contact with parts of the forebrain – the
mammillary bodies (from the Diencephalon) and hypothalamus (of the diencephalon).
Cerebral peduncles …

8. The cerebral peduncles each form a lobe ventrally of the tegmentum, on either side of the
midline. Beyond the midbrain, between the lobes, is the interpeduncular fossa, which is a cistern
filled with cerebrospinal fluid.
The majority of each lobe constitutes the cerebral crus. The cerebral crus are the main tracts
descending from the thalamus to caudal parts of the central nervous system; the central and
medial ventral portions contain the corticobulbar and corticospinal tracts, while the remainder of
each crus primarily contains tracts connecting the cortex to the pons. Older texts refer to the
crus cerebri as the cerebral peduncle; however, the latter term actually covers all fibres
communicating with the cerebrum (usually via the diencephalon), and therefore would include
much of the tegmentum as well. The remainder of the crus pedunculi – small regions around the
main cortical tracts – contain tracts from the internal capsule.
The portion of the lobes in connection with the tegmentum, except the most lateral portion, is
dominated by a blackened band – the substantia nigra (literally black substance)[8] – which is the
only part of the basal ganglia system outside the forebrain. It is ventrally wider at the rostral end.
By means of the basal ganglia, the substantia nigra is involved in motor-planning, learning,
addiction, and other functions. There are two regions within the substantia nigra – one where
neurons are densely packed (the pars compacta) and one where they aren't (the pars reticulata),
which serve a different role from one another within the basal ganglia system. The substantia
nigra has extremely high production of melanin (hence the colour), dopamine, and noradrenalin;
the loss of dopamine-producing neurons in this region contributes to the progression of
Parkinson's disease.[10]
Brain anatomy – forebrain, midbrain, hindbrain.
Development

9. During embryonic development, the midbrain (also known as the mesencephalon) arises from
the second vesicle of the neural tube, while the interior of this portion of the tube becomes the
cerebral aqueduct. Unlike the other two vesicles – the forebrain and hindbrain – the midbrain
does not develop further subdivision for the remainder of neural development. It does not split
into other brain areas. while the forebrain, for example, divides into the telencephalon and the
diencephalon.[11]
Throughout embryonic development, the cells within the midbrain continually multiply; this
happens to a much greater extent ventrally than it does dorsally. The outward expansion
compresses the still-forming cerebral aqueduct, which can result in partial or total obstruction,
leading to congenital hydrocephalus.[12] The tectum is derived in embryonic development from
the alar plate of the neural tube.
The mesencephalon is considered part of the brainstem. Its substantia nigra is closely
associated with motor system pathways of the basal ganglia. The human mesencephalon is
archipallian in origin, meaning that its general architecture is shared with the most ancient of
vertebrates. Dopamine produced in the substantia nigra and ventral tegmental area plays a role
in movement, movement planning, excitation, motivation and habituation of species from
humans to the most elementary animals such as insects. Laboratory house mice from lines that
have been selectively bred for high voluntary wheel running have enlarged midbrains.[13]
The
midbrain helps to relay information for vision and hearing.
Mesencephalon of human embryo
Function
Related terms

10. The term "tectal plate" or "quadrigeminal plate" is used to describe the junction of the gray and
white matter in the embryo. (ancil-453 (http://braininfo.rprc.washington.edu/Scripts/ancilcentral
directory.aspx?ID=453) at NeuroNames)
Wikimedia Commons has media related to Mesencephalon.
Look up midbrain in Wiktionary, the free dictionary.
List of regions in the human brain
1. "mesencephalon" (https://oed.com/search?searchType=dictionary&q=mesencephalon) . Oxford English
Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership (https://w
ww.oed.com/public/login/loggingin#withyourlibrary) required.)
2. Breedlove, Watson, & Rosenzweig. Biological Psychology, 6th Edition, 2010, pp. 45-46
3. Mosby's Medical, Nursing & Allied Health Dictionary,≈ Fourth Edition, Mosby-Year Book 1994, p. 981
4. "Archived copy" (https://web.archive.org/web/20110427225104/http://www.morris.umn.edu/~ratliffj/ima
ges/brain_slides/slide_5.htm) . Archived from the original (http://www.morris.umn.edu/~ratliffj/image
s/brain_slides/slide_5.htm) on 2011-04-27. Retrieved 2011-03-05.
5. Kandel, Eric (2000). Principles of Neural Science (https://archive.org/details/isbn_9780838577011/pag
e/669) . McGraw-Hill. pp. 669 (https://archive.org/details/isbn_9780838577011/page/669) . ISBN 0-
8385-7701-6.
. Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
7. Ferrier, David (1886). "Functions of the optic lobes or corpora quadrigemina" (http://psycnet.apa.org/boo
ks/12789/005) : 149–173. doi:10.1037/12789-005 (https://doi.org/10.1037%2F12789-005) .
. Martin. Neuroanatomy Text and Atlas, Second edition. 1996, pp. 522-525.
9. Haines, Duane E. (2012). Neuroanatomy : an atlas of structures, sections, and systems (https://archive.or
g/details/neuroanatomyatla00hain_570) (8th ed.). Philadelphia: Wolters Kluwer/ Lippincott Williams &
Wilkins Health. pp. 42 (https://archive.org/details/neuroanatomyatla00hain_570/page/n55) . ISBN 978-
1-60547-653-7.
See also
References

11. Last edited 8 months ago by 150.135.165.24
Retrieved from
"https://en.wikipedia.org/w/index.php?
title=Midbrain&oldid=1051301047"
10. Damier, P.; Hirsch, E. C.; Agid, Y.; Graybiel, A. M. (1999-08-01). "The substantia nigra of the human brainII.
Patterns of loss of dopamine-containing neurons in Parkinson's disease" (https://doi.org/10.1093%2Fbrai
n%2F122.8.1437) . Brain. 122 (8): 1437–1448. doi:10.1093/brain/122.8.1437 (https://doi.org/10.1093%
2Fbrain%2F122.8.1437) . ISSN 0006-8950 (https://www.worldcat.org/issn/0006-8950) .
PMID 10430830 (https://pubmed.ncbi.nlm.nih.gov/10430830) .
11. Martin. Neuroanatomy Text and Atlas, Second Edition, 1996, pp. 35-36.
12. "Hydrocephalus Fact Sheet" (http://www.ninds.nih.gov/disorders/hydrocephalus/detail_hydrocephalus.
htm) . National Institute of Neurological Disorders and Stroke. February 2008. Retrieved 2011-03-23.
13. Kolb, E. M.; Rezende, E. L.; Holness, L.; Radtke, A.; Lee, S. K.; Obenaus, A.; Garland (2013). "Mice
selectively bred for high voluntary wheel running have larger midbrains: support for the mosaic model of
brain evolution" (https://doi.org/10.1242%2Fjeb.076000) . Journal of Experimental Biology. 216 (3):
515–523. doi:10.1242/jeb.076000 (https://doi.org/10.1242%2Fjeb.076000) . PMID 23325861 (https://p
ubmed.ncbi.nlm.nih.gov/23325861) .