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A Mesencephalon Decathlon

A Mesencephalon Decathlon. Jim Thorpe Gold medal in the 1912 Olympic decathlon. Questions. What are the 3 primary brain vesicles? What are the corpora quadrigemina? Which anatomic structures comprise the basis pedunculi? What is Claude syndrome? What is a rubral tremor?. Outline.

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A Mesencephalon Decathlon

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  1. A Mesencephalon Decathlon Jim Thorpe Gold medal in the 1912 Olympic decathlon

  2. Questions • What are the 3 primary brain vesicles? • What are the corpora quadrigemina? • Which anatomic structures comprise the basis pedunculi? • What is Claude syndrome? • What is a rubral tremor?

  3. Outline • Embryology • External anatomy • Internal anatomy • Vascular supply • Stroke syndromes • Herniation syndromes

  4. Embryology

  5. 1 of 3 primary brain vesicles • Prosencephalon • Mesencephalon • Rhombencephalon

  6. Intermediate zone gives rise to alar and basal plates • Alar = colliculi, red nucleus and substantia nigra • Basal = general somatic efferent (CN III & IV) and general visceral efferent (E-W nucleus) • Crus cerebri arise from cells outside the mesencephalon

  7. External Anatomy

  8. Crus cerebri • Bordered anteriorly by optic tract • CN III exit medial edge of crus cerebri and pass through interpeduncular fossa

  9. Corpora quadrigemina = 4 colliculi • CN IV marks midbrain/pons junction • SC brachium leads to pulvinar nucleus • IC brachium leads to MGB

  10. Anterior subarachnoid space = interpeduncular cistern • Posterior subarachnoid space = quadrigeminal cistern

  11. Internal Anatomy

  12. 3 divisions • Tectum (roof) • Tegmentum (floor) • Basis pedunculi (crus cerebri + substantia nigra) • Cerebral peduncle = crus +basis pedunculi

  13. Ascending and descending pathways

  14. Caudal Midbrain • Inf Colliculi receive auditory input from lateral lemniscus • PAG involved in pain modulation (connections to thalamus, hypothalamus and somatosensory input) • Fronto-, parieto-, occipito- & temporopontine fibres project to pons and enter MCP

  15. Caudal Midbrain • CN IV axons pass postero-lateral, crossing midline

  16. Somatotopographic organization of the medial lemniscus

  17. Rostral Midbrain • SN • Pars compacta = output to corpus striatum • Pars reticulata = output to thalamus

  18. Rostral Midbrain • RN • Input from contra cerebellum & ipsi cortex • Rubrospinal and rubro-olivary tracts

  19. Diencephalon-mesencephalon junction • Edinger-Westphal nucleus • Output to ciliary ganglion • Input from pretectal neuclei

  20. Diencephalon-mesencephalon junction

  21. Reticular nuclei • Part of ascending reticular activating system • Responsible for alert, wakeful state • Raphe nuclei • Modulate activity in sleep/dream cycles

  22. Vascular Supply Stroke Syndromes Herniation Syndromes

  23. Vascular supply • Branches of SCA and PCA • Lateral midbrain also supplied by anterior choroidal artery (branch of ICA)

  24. Weber • Ipsi CN III, contra bulbar motor • Claude • Ipsi CN III, contra tremor, ataxia and incoordination • Benedikt • Weber + Claude

  25. Central/transtentorial herniation • Upward cerebellar herniation • May lead to • Cerebellar stroke from SCA occlusion • Hydrocephalus from aqueduct compression

  26. Uncal herniation • Lesion most often in temporal lobe • Ipsi CN III is often earliest sign

  27. Questions • What are the 3 primary brain vesicles? • What are the corpora quadrigemina? • What anatomic structures comprise the basis pedunculi? • What is Claude syndrome? • What is a rubral tremor?

  28. Rubral tremor (aka Holme’s tremor) • A coarse, slow (4Hz) tremor, especially present in the upper extremities, that is found at rest, postural and intention.

  29. The End

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