Midbrain

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The mid brain /mesencephalon/ is the most rostral part of the Brainstem, and it builds on the Varol's bridge.

It connects the rhombencephalon to the diencephalon. It measures about 2cm in length. Practically all of it is covered by the hemispheres of the endbrain, only its ventral part is visible as the so-called crura cerebri (partes anteriores pedunculi cerebri) – massive trunks containing white matter. The middle brain runs through the aquaeductus mesencephali' (Sylvii) - a narrow channel, leading cerebrospinal fluid, after a distance from IV. ventricles.

Aquaeductus m. is lined with a layer of gray matter substantia grisea centralis.

The midbrain can be divided into several parts - the tectum mesencephali and the pedunculus cerebri (which consists of the tegmentum mesencephali and the crura cerebri).

Pedunculus cerebri is placed ventrally from the aquaeductus muscle.

 Crura cerebri  (partes anteriores pedunculi cerebri) – also part of the pedunculus cerebri. They are lateral and sink under the optic tract into the base of the brain.

Between the two trunks is the fossa interpeduncularis. Its surface is perforated the course of a series of vessels, therefore it is called ''substantia perforanta posterior' (interpeduncularis). Be careful not to confuse the substantia perforanta anterior, which is part of the endbrain!

In the fossa interpeduncularis, medially from the pedunculi, the n. oculomotor III.

Ventral from the fossa interpeduncularis are the corpora mamillaria, which already belong to the diencephalu. The following cranial nerves depart from the midbrain – III, IV (II runs here already as a pathway, not the optic nerve). The cranial ends of the reticular formation also extend here.

Tectum, "quadrupedal" in English, lies dorsal to the aquaeductus mesencephali. It contains two pairs of bumps - colliculi superiores et inferiores.

They are involved in the visual pathway and the auditory pathway and continue as brachium colliculi superioris et inferioris to the corpus geniculatum laterale a mediale''' diencephalon.

Caudal to the colliculi, the pedunculi cerbellares superiores extend, another in the series of cerebellar pathways. As with the pedunculi cerebellares inferiores, the velum, more precisely, the velum medullare superius, forming the cranial part of the IV ceiling, is opened here. chambers. Cranially from the tectum is the area pretectalis, which already belongs to the diencephalon.

 Nuclei of the tectum mesencephali : 

- predominantly sensitive pathways (sight and hearing)

a) Nc. colliculi superioris - vlákna zo sietnice oka aj motorické a somatosenzitívne

b) Nc. colliculi inferioris - sluchové kôrové centrum

c) Nc. commissurae posterioris

d) Ncc. pretectales - nc. tractus optici

 Tegmentum  (partes posteriores pedunculi cerebri) – ventrálně od tecta, součást pedunculus cerebri.

Hranica medzi crura a tegmentum tvorí substantia nigra.

Substantia nigra - pigment v perikaryách, vonkajšia časť smeruje ku crura a má sieťovitý vzhľad ( pars reticularis ) a vnútorná časť smeruje k tegmentum ( pars compacta ) produkuje dopamín.

Obsahuje řadu důležitých drah a jader. Na boční straně je viditelné jemné vyvýšení – trigonum lemnisci, kde probíhá lemniscus medialis.

 Jadrá tegmentum mesencephali : 

- prevažne motorické dráhy

a) Nc. ruber - oválne, veľké, červenkasté, medzi substantia nigra a aquaeductus, regulácia pohybov končatín

b) Nc. nervi oculomotorii - pri aquaeductus, súbor viacerých jadier, vysiela somatomotorické vlákna do n. oculomotorius, ktoré inervujú 4 zo 6 okohybných svalov, riadi pohyby očnej gule

c) Nc. accessorius n. oculomotorii - dorzálne od nc. nervi oculomotorii, visceromotorické parasympatikové vlákna, m. ciliaris a sphincter pupillae, pohyby očnej gule

d) Nc. interstitialis Cajal - malé, dorzálne od nc. nervi oculomotorii, súvisí so sivou hmotou substantia grisea centralis a s rostrálnou časťou formatio reticularis, súčasť fasciculus longitudinalis medialis

e) Nc. Darkševiči - malé, vlákna z cerebella, kôry telencefala, vestibulárnych jadier rombencefala

f) Nc. nervi trochlearis - malé, pri substantia grisea centralis, kaudálne od n. III, somatomotorické vlákna inervujú m. obliquus superior bulbi

g) Nc. mesencephalicus nervi trigemini - dlhé a štíhle, ide sem z rombencefala, laterálne od aquaeductus, senzitívne svalové a kĺbové receptory žuvacieho svalstva, artic. temporomandibularis a okohybné svaly

Dráhy mesencephala :

- aferentné do ncc. collicules superiores zo sietnice oka, z miechy, rombencefala, zo zrakovej kôry

- do colliculi inferioris z ncc. cochleares

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