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What are the components of the limbic system

1. Limbic cortex
2. Subcortical limbic structures

3. Fibers


What are the subcomponents of the limbic cortex

1. Parahippocampal gyrus
2. Hippocampal formation

3. Dentate gyrus

4. Cingulate gyrus

5. Insula

6. Orbitofrontal gyrus


What are the subcortical limbic structures involved in the limbic system

1. Amygdala
2. Hypothalamus

3. Septal nuclei

4. Habenular nuclei

5. Anterior and dorsomedial thalamic nuclei

6. Indusium griseum


What are the fibers/tracts involved in the limbic system

1. Mamillothalamic tract
2. Fornix

3. Stria medullaris thalami

4. Stria terminalis


What are the layers of the hippocampus

1. Presubiculum
2. Subiculum

3. Prosubiculum

4. Hippocampus

5. Dentate gyrus

All of these layers are archipallum, that is they are composed of three layers - molecular, pyramidal and polymorphic.


The inferior parahippocampal gyrus is what type or cortex?

Isocortex - it has 6 layers. 


What is the indusium griseum

Hippocampal remnants that course over the dorsal surface of the corpus callosum and connect the septal area with the hippocampus.

Composed of the subcallosal gyrus and the medial and lateral longitudinal striae.


Input to the hippocampal gyrus

1. Entorhinal cortex --> hippocampal and dentate gyrus.

2. Medial septal nucleus --> Fimbria

3. Cingulate gyrus --> cingulum --> presubiculum/entorrhinal cortex --> hippocampus


What are the components of the fornix

1. Fimbriae
2. Crura

3. Body

4. Columns.


What are the output fibers/tracts located within the fornix

1. Precommissural fornix --> caudate septal nucleus
2. Postcommissural fornix --> mammillary bodies --> anterior thalamic nulcei --> cingulate gyrus

3. Subiculum --> postcommissural fornix ---> various structures.


Hippocampal output from the subiculum leaves via the postcommissural fornix and travels to the 5 following structures: 

1. Mammillary bodies
2. Anterior thalamic nuclei

3. Lateral septal area of the hypothalamus

4. Medial frontal cortex

5. Cingulate gyrus


What is the sole direct cortical projector/output of the hippocampus

The subiculum. Dentate fibers do not leave the hippocampus. 


CA1 pyramidal cell axons project to the 

Subiculum and fornix


CA3 pyramidal cell axons project to the 

CA1 and fornix


What is the function of the hippocampus

Consolidation of short-term memory into long-term memory. Unilateral injury to mammillary bodies or the fornix does not seem to impair function but lesions to this area may cause psychomotor seizures. 


What is the circuit of Papez

A bidirectional connection from the subiculum--> mammillary bodies --> mammillothalamic tract --> anterior thalamic nucleus --> entorhinal cortex --> subiculum.

Involved with emotion.


What are inputs to the amygdala

1. Locus ceruleus - noradrenergic fibers
2. SN and ventral tegmentum - dopaminergic fibers

3. Substantia innominata and lateral olfactory area - cholinergic fibers

4. Raphe nucleus - serotonergic fibers


What are the main outputs of the amygdala?

1. Stria terminalis --> nucleus of the stria terminalis --> hypothalamus
2. Ventral amygdalofugal tract --> to various areas including the brainstem nuclei to regulate autonomic functions dealing with fear or stress.

3. Amygdalocortical

4. Amygdalostriate --> nucleus accumbens


What is the other name for the substantia innominate and where is it located

Nucleus basalis of Meynert

It is located in the basal forebrain and extends from the olfactory tubercle to the hypothalamus


What is the input and output of the substantia innominate/nucleus basalis of Meynert

Input: amygdala, temporal lobe, pyriform cortex, and entorhinal cortex.

Output: Diffuse cortical outputs.


Features of the substantia innominata

High concentration of cholinergic fibers and the sole source of the cholinergic output to the cortex.

These cells degenerate in the setting of Alzheimer's disease


What are the cholinergic areas of the CNS. 

1. Substantia innominata/nucleus basalis of Meynert
2. Pedunculopontine nucleus

3. Lateral dorsal tegmental nucleus

4. Medial habenular nucleus