Outline for today
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Transcript of Outline for today
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Outline for today
• Structures
• Cell types
• Circuitry
• Function
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structure
• c-shaped in coronal or transverse sections• outline resembles rams horn (Ammons horn)• dorsal and ventral commissures
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major components of the hippocampal formation
• hippocampal proper (CA1,CA2,CA3)• dentate gyrus• entorhinal cortex• Subiculum• Presubiculum• parasubiculum
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How many cell layers are in…
• Dentate gyrus
• Hippocampal proper
• Entorhinal cortex
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3 main Layers of DG
• molecular layer
• granule cell layer (striatum granulosum)
• polymorphic (or hilus)
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3 main layers of hippocampus
• molecular layer (stratum radiatum. stratum lacunosum, moleculare)
• pyramidal layer – stratum pyramidale
• polymorphic (stratum oriens)
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DG cell types
• diverse variety of interneurons
• mossy fibers – axons from DG granule cells – unmyelinated axons – synapse on CA3– only excitatory output from DG
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basket cells
• axons form plexuses surrounding cell body of granule cells– GABA
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cells and layers of the dentate gyrus
1- granule cell; axons (mossy fiber) – collateralize in PL and then to CA32- dentate pyramidal basket cell 3 – stellate cells (give rise to basket plexus)4- mossy cell (GLU) 5- inhibitory cells
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DG
• studied in relation to kindling, LTP
• DG has the most consistent cell loss in temporal lobe epilepsy – (in part interneurons in the hilus of DG)
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typical CA1 pyramidal cell
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some of the connections • mossy fibers – axons from DG granule
cells – unmyelinated axons – synapse on CA3– sole excitatory output from DG– multiple granule cells can synapse on a single
pyramidal cell
• Schaffer collaterals- projections from CA3 to CA1 (ipsilateral and contralateral)
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some of the connections • perforant pathway – major input to
hippocampus– axons arise primariy from layers II and III of
EC
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Alveus
Entorhinal cortex (perforant path)
Recurrent (Schaffer) collateralsof hippocampal pyramidal cells inCA3
Raphe, septal region
Commissural axons; intrinsic short axoncells
Basket cells
Short axon cells; commissural axons
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some more connections
• alveus - thin layer of fibers originating from pyramidal cells and subiculum; on route to subcortical termination or contralateral hipp– covers the ventricular surface of the
hippocampus– bundle thickens – lateral extreme end of hipp
– fimbria; descending into forebrain - fornix.
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What are the main afferents to hippocampus and DG?
• entorhinal cortex***• septum, contralateral hippocampus
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Cortical inputs to the hippocampal formation
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What are the afferents to the entorhinal cortex?
• projections from brainstem, raphe, LC, VTA, • hypothalamic afferents• thalamic nuclei• telencephalic cortical areas• other hippocampal regions
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Hippocampal Efferents
• Many fibers sent directly back to the entorhinal cortex.
• Most anatomically prominent output pathway is the fornix
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efferents of EC
• perforant pathway• amygdala, cortical nuclei, central nucleus,
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Subcortical outputs via the fornix
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Cortical projections from hippocampus via entorhinal cortex
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subiculum
• one of most important efferents of hippocampal formation – only its axons leave the telencephalon to terminate in the diencephalon
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fimbria/fornix
• carry efferent from hippocampal formation and subcortical afferent fibers to hippocampus
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trisynaptic circuit
• perforant pathway synapse on granule cells
• granule cells send their mossy fiber axons to CA3
• CA3 pyramidal cells send their shaffer collateral axons to CA1
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neurotransmitters?
• GLU– perforant path, mossy fibers, Schaffer collaterals,
excitatory interneurons– NMDA and metabotropic R
• GABA• 5HT