Covers the midbrain's position between the pons and diencephalon, its length and cranial nerve nuclei III and IV, then its external and internal features: the tectum with superior and inferior colliculi, the tegmentum, and the cerebral crus. Two cross-sections at the inferior colliculus level list the nuclei, such as the substantia nigra, red nucleus and periaqueductal grey, and the ascending and descending tracts running through them.
Topic 131 of 236 in the MU Pleven syllabus for Anatomy Bones and Muscles (Medicine, Year 2). The free AceMed note covers it in 4 sections, about 591 words (4 min of reading), with 10 flashcards.
In this note
MIDBRAIN (MESENCEPHALON)
External & Internal features :
Caudal Section at the level of the inferior Colliculus :
Rostral Section at the level of inferior colliculus :
MIDBRAIN (MESENCEPHALON)
Located above Pons, infront of the cerebellum and below the diencephalon
Is the most superior of the three regions of the brainstem.
Length ~ 2cm (the shortest part of the brainstem).
Contains nuclei for CN.(III, IV)
External & Internal features :
1 Tectum of midbrain (tectum mesencephali)
– the dorsal part of the midbrain
– formed by the superior (elevation) and inferior colliculi
1.1 Superior colliculus (colliculus superior)
– a division of the visual pathway enters into the layers lying under this structure
– consists of seven layers of grey and white matter (laminae), which have a retinotopic organisation
– responsible for the rapid eye movement phase of sleep
– its function is associated with rapid and controlled eye movement
– the brachium of superior colliculus connects the superior colliculus with the lateral geniculate body
1.2 Inferior colliculus (colliculus inferior)
– the third order neurones of the auditory pathway are located here
– contains three nuclei with tonotopic organization
– the brachium of colliculus inferior connects the inferior colliculus with the medial geniculate body
2 Tegmentum of midbrain (tegmentum mesencephali)
2.1 Aqueduct of midbrain (aqueductuc mesencephali Sylvii)
2.6 Superior cerebellar peduncles (pedunculi cerebellares superiores) – connect the midbrain and cerebellum, contain afferent and efferent cerebellar tracts
3 Cerebral crus (crus cerebri/mesencephali) – the ventral paired part containing descending tracts
4 Pretectal area (area pretectalis) – a group of four small nuclei in front of the lateral border of the superior colliculus, situated at the borderline between the midbrain and epithalamus
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