Limbic System Overview and Key Components

Study Notes

The limbic system is involved in emotion, behaviour, mood, and memory.
Initially, a significant role of the limbic system was thought to be linked to olfaction (sense of smell).
Key components include the hippocampus, fimbria, fornix, dentate gyrus, mammillary body, uncus, cingulate gyrus, parahippocampal gyri, amygdaloid body, septal areas and piriform areas, and anterior thalamic nucleus.

Situated above the anterior part of the parahippocampal gyrus.
Projects onto the floor of the inferior horn of the lateral ventricle.
The anterior portion of the hippocampus is called pes hippocampi.
Alveus is a thin film of white matter that thickens medially to form the fimbria.
Alveus separates from the hippocampus as the crus of the fornix.
The dentate gyrus is part of the hippocampus located between the fimbria and the parahippocampal gyrus.

A major efferent pathway from the hippocampus.
Also functions as an association tract and commissure (connecting different parts of the brain).
Fibers originating from the anterior column of the fornix extend both anteriorly and posteriorly to the anterior commissure.
Anterior fibres in the fornix connect to septal nuclei.
Posterior fibres in the fornix connect to the thalamus and mamillary bodies.
Mamillo-thalamic tract connects the mamillary bodies to the anterior nucleus of the thalamus.
Fibers in the fornix run through the internal capsule to reach the cingulate gyrus.

A circuit of interconnected structures involved in emotion and memory.
Key structures involved in the circuit include the hippocampus, mamillary body, anterior thalamus, cingulate gyrus, and fornix.

Composed by gray matter above the lamina terminalis, near the anterior commissure.
A part of the septal area is the septum pellucidum.

Olfactory tract runs through the olfactory sulcus beside the gyrus rectus.
The anterior end expands to form the olfactory bulb.
Second-order neuron cells are located within this pathway.
Axons from these cells travel back through the tract.
At the anterior perforated substance, the tract divides, with lateral striae extending to the uncus and medial striae connecting to other limbic system parts.

This section discusses the functions of the limbic system and potential associated disorders.

Most of the limbic system output connects to the hypothalamus primarily through the medial forebrain bundle.

Hypothalamic regions are connected to eating, drinking, and sexual behaviour patterns.
Lesions in the lateral amygdala cause unrestrained eating (bulimia).
Lesions in the medial amygdala cause anorexia and hypersexuality.
Electrical stimulation of the amygdala may induce fear and anxiety in humans.

The hippocampus plays a vital role in converting short-term memory into long-term memory (up to 60 minutes to several days or longer).
Bilateral hippocampal damage causes profound anterograde amnesia.

The hippocampus contains "place cells" that encode spatial memory (where you have been).
Recalling locations and routes to navigate requires hippocampal activation.