Limbic System
Limbic system consists of: hippocampus, amygdala, septal nuclei, entorhinal cortex, and parahippocampal cortex.
Hippcampusà cornu ammonis or Ammon’s horn
Fornix
-C shaped tract beginning as the alveus
-Alveus-myelinated afferents and efferents to become fibria
-Fimbria- thick rubber band of fibers to split into crura
-Crura- come together to form hippocampal commissure which is mode of communication between the hippocampi
-after comminsureà fornix proper to become anterior commissure
Anterior Commissure
-Precomissural Fornix-to septal nuclei, substantia innominata, cingulated cortex
-Anterior Commissure Proper- to contralateral hippocampus
-Post Commissure Fornix- mammillary bodies and anterior nuclei
Substanita Innominata/Nucleus Basilis/ Basalis nucleus of Meynert
-below globus pallidus
-projections to cortex and back
-cholinergic innervation
-**indicated in ALZHEIMERS disease, memory association
Connections from the Postcommisural Fornixàmammilary bodies; Degeneration in Korsakoff Syndrome present with difficulty forming NEW MEMORIES. Mam. Bodies connect to the cingulated cortex/enterhinal cortex completed PAPEZ circuità critical in memory/emotional formation.
Two major input/output pathways of hippocampus: 1)entorhinal cortex 2)fornix
Entorhinal cortex connects to the amygdala via the SUBICULUM.
Major Pathway of limbic system (KNOW THIS!)
Frontal/Temporal/Pareital Cortex Parahipocampal/Perihinal Cortexà Entorhinal Cortex
Perforant pathway Dentate (Mossy Fiber Pathway)
Hippocampus CA3 (Schaffer Collateral pathway)
Hippocampus CA1
Subiculum back to entorhinal cortex
All communication in hippocampus is BIDIRECTIONAL.
Inputs to hippocampus from entorhinal cortex and C.O.T.O. N.
-Cingulate Cortex
-Orbital Cortex
-Temporal Lobe Cortex
-Olfactory Bulb
-Neocortex
Hippocampus and DENTATE gyrus process the information which pass through the hippocampus. Evolves from a 3 layer to a SIX layer structure. (transition occurs in subiculum-connects parahippocampus to hippocampus). Middle layerà pyramidal cells. CA3 areaà capping of dentate gyrus
Pyramidal cells of middle hippocampus
-parallel dendrites (hyperexcitability Epilelpsy)
-increase electrical conductance (EEG)
-perpendicular to the cortex
-dendritic spines with Basket cells
-glutamate excitatory neurons
-Basket Cells INHIBIT constant firing of dendritic cells; if this does not occurà temporal lobe EPILEPSY; secretes GABA
- Epilepsy- thousands of neurons firing at once, breakdown of synaptic inhibition
-Picrotoxinà increase firingà increase seizure
Long term potnetiation in Schaffer Pathway: occurs due to a post-synaptic event, via NMDA receptors (displacement of Mg+2), requires a strong signal. LONG TERM MEMORY.
Long term potentiation in Mossy Pathway: Short term memory
Amygdala
-integrative center for emotion, behavior and motivation
-commincates bidirectionally with rest of brain
-Inputs: hypothalamus, septal area, orbital cortex, parabrachial nucleus, olfactory bulb
-Outputs: ventral amygdofugal pathway, stria terminalis, hippocampus
-controls RAGE and FEAR
-irrtitave lesions of the temporal cortexà panic attacks initiated in amygdala
-Lesions of Amygdala: calmness, loss of emotion, loss of emotional implications in face
-recoginition of rewards, “how sweet it is”
- controls fear conditioning
- controls emotional learning by inducing emotional/sympathetic/autonomic responses to fearful stimuli
Ventral Amygdofugal Pathway
-connects amygdala to
-anterior olfactory nucleus
-priform cortex
-cingulate cortex
-ventral striatium
-important link in MOTIVATION and DRIVE
Stria Terminalis
-annalogous to fornix in hippocampus
-connects only to subcortical structures
-to septal nuclei
-precommisural branchà septal area
-postcommussural branchà hypothalamus
-acts as a pathway by which the two amygdala communicate with each other
Tags: amygdala, entorhinal cortex, fornix, hippocampus, Mossy Pathway, parahippocampal cortex, Schaffer Pathway, septal nuclei, Stria Terminalis, Ventral Amygdofugal Pathway
