Anatomy (CNS) · MU Sofia

158. Mesencephalon (Midbrain).

Covers the midbrain's position and length, then its external and internal features: the tectum with the superior and inferior colliculi, and the tegmentum with the aqueduct, periaqueductal grey, reticular formation and decussations. Cross-sections at the inferior colliculus level list the cranial nerve nuclei, dopamine-rich substantia nigra and descending and ascending tracts. The note ends with a rostral section at the same level, covering the oculomotor nuclei, red nucleus and related structures.

Inside: 4 sections · 7 labelled pictures · 10 flashcards · 4 min

Topic 16 of 34 in the MU Sofia syllabus for Anatomy (CNS) (Medicine, Year 2). The free AceMed note covers it in 4 sections, about 578 words (4 min of reading), with 10 flashcards.

In this note

  1. MIDBRAIN (MESENCEPHALON)
  2. External & Internal features :
  3. Caudal Section at the level of the inferior Colliculus :
  4. Rostal 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. 1 Tectum of midbrain (tectum mesencephali)
  • the dorsal part of the midbrain
  • formed by the superior elevation and inferior colliculi
  1. 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. 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
  1. 2 Tegmentum of midbrain (tegmentum mesencephali)
  2. 2.1 Aqueduct of midbrain (aqueductuc mesencephali Sylvii)
  1. 2.2 Periaqueductal grey substance (PAG; substantia grisea centralis)
  2. 2.3 Reticular formation (formatio reticularis)
  3. 2.4 Nuclei and tracts of the cranial nerves
  4. 2.5 Specific nuclei and tracts of the brainstem
  5. 2.5.1 Posterior tegmental deccusation (decussatio tegmentalis posterior)
  • a crossing of the tectospinal tract
  1. 2.5.2 Anterior tegmental deccusation (decussatio tegmentalis anterior)
  • a crossing of the rubrospinal tract
  1. 2.6 Superior cerebellar peduncles (pedunculi cerebellares superiores) – connect the midbrain and cerebellum, contain afferent and efferent cerebellar tracts
  2. 3 Cerebral crus (crus cerebri/mesencephali) – the ventral paired part containing descending tracts
  3. 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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