Limbic System - Memory Circuits Flashcards
What structures are responsible for declarative and non-declarative memory?
Declarative - Hippocampus
Non-Declarative - Amygdala and Motor system
Name the three formations in the hippocampal formation:
Dentate Gyrus, Hippocampus, Subiculum
Name the three layers of dentate gyrus:
Polymorphic, granular, molecular
Which cell layer is the main output of the dentate gyrus?
granular
What are the projection targets of mossy fibers in dentate gyrus?
Apical dendrites of pyramidal neurons in CA3/CA4.
How many divisions are there of hippocampus proper? What are these divisions called? What is their main output?
Four cornu ammonis (CA) fields. Principle output are glutamatergic pyramidal cells.
Give the steps of the trisynaptic pathway:
entorhinal cortex -perforant pathway> dentate gyrus -mossy fibers of granular cells> CA3 -Schaffer Collaterals> CA1.
What makes the hippocampal formation so susceptible to epileptic seizures?
The trisynaptic pathway consists of largely excitatory glutamatergic neurons. Thus imbalances in ion concentrations causing depolarized membrane potentials make seizure much more likely.
What is long term potentiation?
Increased synaptic strength following repeated use.
Describe the output pathway of the hippocampal formation:
Outputs from the CA layers and the subiculum form the alveus. As they depart the hippocampal formation they form the fimbria then merge tighter together to form the fornix.
What are the projection targets of the hippocampus and where do these projections originate?
Post commisural fibers: Anterior nucleus of thalamus (subiculum), mammillary bodies (subiculum),
Precommisural fibers: septal nuclei (CA fields), ventral striatum (CA fields).
What inputs are received by the hippocampal formation?
Perforant pathway: entorhinal cortex, posterior cingulate, orbital cortex (uncinate fasciculus)
Fornix: septal nuclei (cholinergic)
The hippocampal formation receives inputs from entorhinal cortex, but where do inputs to entorhinal cortex come from?
Association areas of cortex project to parahippocampus and perirhinal cortex which, in turn, project to entorhinal cortex. Thus hippocampus receives integrated information from diverse modalities.
Memory deficits in alzheimers are associated with loss in which areas related to the hippocampus?
Hippocampus proper, subiculum, entorhinal cortex, association areas of cortex, ventral septum (NBM)
Relate ischemia and seizure susceptibility:
ischemia will cause damage to neurons that transmit glutamate. Excessive glutamate activates NMDA receptors on inhibitory GABA-ergic interneurons allowing large influx of Ca++. Excessive CA++ activates proteases that destroy cellular machinery in inhibitory interneurons leaving reduced inhibition and increased seizure susceptibility.
