Form from 2 Arcs
- Outer arc
- Parahippocampal gyrus
- Cingulate gyrus (also called the limbic gyrus)
- Subcallosal area (paraolfactory area)
- Inner arc
- Hippocampal formation
- Fornix
- Septal area (also known simply as the septum)
- Diagonal band of Broca (not visible in this view)
- Paraterminal gyrus
Components of the Limbic System
Cortical regions
Limbic lobe
- Cingulate gyrus
- Isthmus
- Parahippocampal gyrus
- Uncus
Hippocampal formation: C shaped
Hippocampus (cornu ammonis)
- Pes hippocampus: anterior end of hippocampus is expanded and notched and resembles a foot
- Alveus:
- a layer of nerve fibres that covers the ventricular surface of the hippocampus
- The fibres of the alveus pass medially and collect to form fimbria
- Fimbria runs backward to be continuous with the fornix
- Made up of 3 layers
- Superficial molecular layer
- Middle pyramidal cell layer
- Deep polymorphic cell layer
The cerebral cortex that lies below the choroid fissure is S-shaped The superior limb forms the hippocampal formation (cornu ammonis and dentate gyrus).The middle limb of the “S” is called the subiculum. Made up of 5 layersThe lower lip of the “S” is parahippocampal gyrusMade up of 6 layers
- Connection
- Afferent
- Entorhinal area (area 28)
- Olfactory cortex
- Amygdala
- Opposite hippocampus
- Parahippocampal gyrus
- Efferent: fornix is the main efferent tract
- To the opposite hippocampus through the commissure of fornix/hippocampal commissure
- To the septal and anterior hypothalamic regions
- To the mamillary body, which sends impulses to cingulate gyrus through anterior nucleus of thalamus, through Papez circuit
- Papez circuit
- Fx: Short term memory
- Perforant pathway (Entorhinal cortex → perforates through the subiculum → enters and synapse in the Dentate gyrus → (via Schaffer collaterals) → CA3 → CA1 → Subiculum → along the alveus to the fimbria → crux of fornix → mammillary body) → Mamillothalamic tract → Anterior thalamus → anterior thalamic radiation → cingulate gyrus → Cingulum → back to parahippocampal gyrus (entorhinal cortex)
- The perforant pathway
- Mesial temporal lobe connections with the hippocampal formation-part of papez circuit
- Perforant: because it perforates the subiculum
- This is a uni direction pathway
- IC internal capsule
- F Fornix
- MMT: Mamillothalamic tract
- M: mamillary bodies
- HF: Hippocampal formation
- Made up of
- Entorhinal cortex
- Dentate gyrus
- Cornu ammonis CA1-4
- Subiculum
- C: Cingulum
- Mamillothalamic Tract (aka bundle of Vicq d’Azyr) is the bundle of fibres, which carries impulses from mammillary body to the anterior nucleus of thalamus
- Dentate gyrus
- a series of notches that give it a teeth-like (dentate)
- Splenial gyrus (Gyrus fasciolaris)
- Indusium griseum:
- lines the upper surface of the corpus callosum
- Remains underdeveloped
- The remnant of the hippocampus that courses over the dorsal surface of the corpus callosum (the supracallosal gyrus).
- It contains two longitudinally directed strands of fibers termed the medial and lateral longitudinal striae
Septal area
- A part of the septal region which is made up of:
- Precommissural septum: Septal area
- Supracommissural septum: septum pellucidum
- 3 masses of grey matter that lie immediately anterior to the lamina terminalis and the anterior commissure
- Paraterminal gyrus
- Prehippocampal rudiment
- Subcallosal area (or para olfactory gyrus)
- Connections
- Afferent
- Olfactory tract through medial olfactory stria
- Amygdala through Stria Terminalis/Dorsal Amygdalofugal pathway
- Hippocampus through fornix
- Fornix
- Some fibres of the fornix that descend in front of the anterior commissure terminate in septal area.
- Some of these fibres turn backwards to enter the stria medullaris thalami and reach the habenular nuclei.
- Efferent
- Habenular nuclei through stria medullaris thalami (stria habenularis).
Olfactory areas
Subcortical structures
Amygdaloid nuclear complex
- Connections
- Afferent
- Primary olfactory cortex
- Hippocampus
- Hypothalamus
- Thalamus (medial dorsal nucleus)
- Impulse relayed into prefrontal cortex.
- Corpus Striatum
- Ventral striatum
- basal nucleus of Meynert (cholinergic)
- Ventral pallidum
- Cerebral cortex
- Cingulate gyrus
- Parts of the frontal, temporal, and occipital lobes,
- Including the visual and auditory areas.
- Brainstem
- Reticular formation
- Esp: parabrachial nucleus
- Nucleus of solitary tract
- Dorsal nucleus of the vagus
- Efferent fibres from amygdala pass through two major routes:
- Stria terminalis → septal nuclei, olfactory areas
- Ventral amygdalofugal route
- Function:
- Control of emotional behaviour
- Smell mediated sexual behaviour: receive olfactory input
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