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A Mesencephalon Decathlon
Jim Thorpe won decathlon during 1912 olympics in Stockholm when King Gustav V of sweden calle dhim the world’s greatest athlete. 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 Internal anatomy Embryology External anatomy Vascular supply
Stroke syndromes 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 Corpora quadrigemina = quadruplet bodies
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Anterior subarachnoid space = interpeduncular cistern
Posterior subarachnoid space = quadrigeminal cistern
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Internal Anatomy
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Cerebral peduncle = crus +basis pedunculi
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 Lat lemniscus ascends from cochlear nuclei in rostral medulla SCP cerebellar output to RN, thalamus, but also pons and medulla
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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 SN=dopaminergic soma have melanin RN=dnese vascularity, so pink Retiucara = also sup colliculus & pontine reticular formation
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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 Raphe 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 Claude Benedikt Ipsi CN III, contra bulbar motor
Ipsi CN III, contra tremor, ataxia and incoordination Benedikt Weber + Claude Claude takes out RN and cerebellothalamic fibers as well
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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
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