a mesencephalon decathlon
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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A A MesencephalMesencephalon Decathlonon Decathlon
Jim Thorpe
Gold medal in the 1912 Olympic decathlon
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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?
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Outline
1. Embryology
2. External anatomy
3. Internal anatomy4. Vascular supply
5. Stroke syndromes
6. Herniation syndromes
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Embryology
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• 1 of 3 primary brain vesicles– Prosencephalon– Mesencephalon– Rhombencephalon
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• 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
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External Anatomy
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• Crus cerebri– Bordered anteriorly by optic tract
• CN III exit medial edge of crus cerebri and pass through interpeduncular fossa
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• Corpora quadrigemina = 4 colliculi• CN IV marks midbrain/pons junction
• SC brachium leads to pulvinar nucleus• IC brachium leads to MGB
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• Anterior subarachnoid space = interpeduncular cistern
• Posterior subarachnoid space = quadrigeminal cistern
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Internal Anatomy
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• 3 divisions– Tectum (roof)– Tegmentum (floor)– Basis pedunculi (crus cerebri + substantia nigra)
• Cerebral peduncle = crus +basis pedunculi
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• Ascending and descending pathways
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• 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
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• Caudal Midbrain– CN IV axons pass postero-lateral, crossing midline
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• Somatotopographic organization of the medial lemniscus
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• Rostral Midbrain– SN
• Pars compacta = output to corpus striatum• Pars reticulata = output to thalamus
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• Rostral Midbrain– RN
• Input from contra cerebellum & ipsi cortex• Rubrospinal and rubro-olivary tracts
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• Diencephalon-mesencephalon junction– Edinger-Westphal nucleus
• Output to ciliary ganglion• Input from pretectal neuclei
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• Diencephalon-mesencephalon junction
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• Reticular nuclei– Part of ascending reticular activating system– Responsible for alert, wakeful state
• Raphe nuclei– Modulate activity in sleep/dream cycles
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Vascular Supply
Stroke Syndromes
Herniation Syndromes
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• Vascular supply– Branches of SCA and PCA
– Lateral midbrain also supplied by anterior choroidal artery (branch of ICA)
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• Weber– Ipsi CN III, contra bulbar motor
• Claude– Ipsi CN III, contra tremor, ataxia and incoordination
• Benedikt– Weber + Claude
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• Central/transtentorial herniation• Upward cerebellar herniation
– May lead to • Cerebellar stroke from SCA occlusion• Hydrocephalus from aqueduct compression
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• Uncal herniation– Lesion most often in temporal lobe– Ipsi CN III is often earliest sign
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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?
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• 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.
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The End