Limbic systemLimbic systemDr. Mohammad Mahmoud MosaedDr. Mohammad Mahmoud Mosaed

Limbic systemLimbic system Anatomically, the limbic system is a complex network of cortical

areas and subcortical structures interconnected by bidirectional pathways.

Major limbic centers include: The cortical areas: cingulate gyrus, orbitofrontal, insular, and

medial prefrontal cortices and parahippocampal gyrus. Subcortical structures, including: The thalamus (anterior thalamic nuclei), septal area, nucleus

accumbens, hippocampus, hypothalamus (mammillary bodies) and the amygdala (amygdaloid complex).

connecting pathways of limbic system The alveus, the fimbria, the fornix, the mammillothalamic tract,

and the stria terminalis

FUNCTIONS OF THE LIMBIC SYSTEM The limbic system is involved with many of the expressions

that make us human, namely emotions, behavior, and states of feeling

Associated with memory especially the hippocampus. Associated with pleasure and rage The limbic system, via the hypothalamus is able to influence

many aspects of emotional behavior. These include particularly the reactions of fear and anger and the emotions associated with sexual behavior.

There is no evidence that the limbic system has an olfactory function. The various afferent and efferent connections of the limbic system provide pathways for the integration and effective homeostatic responses to a wide variety of environmental stimuli.

The cingulate motor area Site: on the medial surface of

the cerebral hemishere above the callosal sulcus and below the singulate sulcus.

Functions: The cingulate motor area is part of the limbic system. This part of the cortex may be involved in motor responses to drives and emotions.

The cingulum is a fiber bundle that runs from the cingulate gyrus to the parahippocampal gyrus

calcarine sulcus

central sulcuscingulate sulcus

cingulate gyrus

parietooccipital sulcus

Septum

anterior commisurerhinal sulcus

Parahippocampal gyrusParahippocampal gyrus Site: it lies on the

inferior surface of each cerebral hemispher medial to the anterior part of the collateral sulcus

Anteriorly continuous with the uncus

Posteriorly continuous with the cingulate gyrus

Septal area

Site: It lies on the medial surface of cerebral hemishere anterior to the lamina terminalis and anterior commissure, it include the septum pellucidum

Connections

Afferent: hippocampus (through the fornix), amygdaloid body, hypothalamus ( through the medial forebrain bundle)

Efferent: to the hippocampus, hypothalamus, habenular nuclei (though the stria medullaris thalami) and reticular formation of the mid brain

Functions it is regard as pleasure center

Orbitofrontal cortex and Prefrontal Cortex

Orbitofrontal cortex Located on the underside of each cerebral hemisphere (just above the bones of the eye sockets), it is the area that appears to be most directly involved in emotions.

Prefrontal Cortex Areas in the frontal cortex

appear to be involved in planning, problem solving, and in the organizational strategies used in memory tasks.

AmygdalaAmygdala Large nuclear group in temporal lobe.

Almond in shape Relations: It is situated partly anterior

and partly superior to the tip of the inferior horn of the lateral ventricle. It is fused with the tip of the tail of the caudate nucleus. The stria terminalis emerges from its posterior aspect

Divisions Large basolateral region: Provides

direct input to basal ganglia and motor system.

Small corticomedial group of nuclei: Related to olfactory cortex.

Medial and central nuclei: Connected to hypothalamus

Functions of the AmygdalaFunctions of the Amygdala Coordinated behavioral, autonomic

and endocrine responses ( Feeding and drinking, fighting behavior, mating and maternal care and responses to physical or emotional stresses.(

The hippocampal formation The hippocampal formation consists of hippocampus,

dentate gyrus and subiculum The hippocampus is a curved elevation of gray matter

and it is a part of the cerebral cortex enrolled in the floor of the inferior horn during the development. Its anterior end is expanded to form the pes hippocampus

The hippocampus extends throughout the entire length of the floor of the inferior horn of the lateral ventricle

In the coronal section the hippocampus resembles a sea horse

The hippocampus terminates posteriorly beneath the splenium of the corpus callosum.

The convex ventricular surface of the hippocampus is covered with ependyma, beneath which lies a thin layer of white matter called the alveus. The alveus consists of nerve fibers that have originated in the hippocampus, and these converge medially to form a bundle called the fimbria. The fimbria, in turn, becomes continuous with the crus of the fornix. The fornix is the major output channel of the hippocampus

The dentate gyrus The dentate gyrus is a narrow, notched band of gray matter that lies

between the fimbria of the hippocampus and the parahippocampal gyrus, separeted from the parahippocampal gyrus by the para hippocampal sulcus. Anteriorly, the dentate gyrus is continued into the uncus. Posteriorly, the gyrus accompanies the fimbria almost to the splenium of the corpus callosum and becomes continuous with the indusium griseum.

The indusium griseum is a thin, vestigial layer of gray matter that covers the superior surface of the corpus callosum. Embedded in the superior surface of the indusium griseum are two slender bundles of white fibers on each side called the medial and lateral longitudinal striae. The striae are the remains of the white matter of the vestigial indusium griseum.

The subiculum is transitional between the hippocampus and entorhinal cortex (area 28) of the parahippocampal gyrus

Afferent Connections of the Hippocampus Fibers from the cingulate gyrus pass to the hippocampus. Fibers from the septal nuclei (nuclei lying within the midline close

to the anterior commissure) pass posterior in the fornix to the hippocampus.

Fibers from one hippocampus pass across the midline to the opposite hippocampus in the commissure of the fornix.

Fibers from the indusium griseum pass posteriorly in the longitudinal striae to the hippocampus.

Fibers from the entorhinal area or olfactory-associated cortex pass to the hippocampus.

Fibers arising from the dentate and parahippocampal gyri travel to the hippocampus.

Fibers from the thalamus. the anterior nuclei and the midline complex, project to the hippocampal and parahippocampal areas.

Efferent Connections of the HippocampusEfferent Connections of the Hippocampus The fibers within the fornix are distributed to the following

regions: 1. Fibers pass posterior to the anterior commissure to enter the

mammillary body, where they end in the medial nucleus. 2. Fibers pass posterior to the anterior commissure to end in the

anterior nuclei of the thalamus. 3. Fibers pass posterior to the anterior commissure to enter the

tegmentum of the midbrain. 4. Fibers pass anterior to the anterior commissure to end in the

septal nuclei, the lateral preoptic area, and the anterior part of the hypothalamus.

5. Fibers join the stria medullaris thalami to reach the habenular nuclei.

Function of the hippocampus: : Learning and memory

Damage to the hippocampus or its input or output regions and fibers results in memory loss, or amnesia

Damage to both hippocampi results in anterograde amnesia, or the inability to learn new information. Retrograde amnesia, the loss of previously learned information, may be present as well.

The connecting pathways of the limbic system

Fornix It forms the main efferent fibers of the

hippocampus Axons of the large pyramidal cells of the

hippocampus emerge to form the alveus and the fimbria. The fimbria continues as the crus of the fornix. The two crura converge to form the body of the fornix. The body of the fornix splits into the two columns of the fornix, which curve downward and forward in front of the interventricular foramina. Every column terminate into the mammillary body

It projects from the hippocampal formation to the mammillary body of the hypothalamus, septal area and anterior nucleus of the thalamus

Formation and relations of Fornix The alveus consists of a thin layer of white matter that lies on the superior or ventricular

surface of the hippocampus. It is composed of nerve fibers that originate in the hippocampal cortex. The fibers converge on the medial border of the hippocampus to form a bundle called the fimbria.

The fimbria now leaves the posterior end of the hippocampus as the crus of the fornix. The crus from each side curves posteriorly and superiorly beneath the splenium of the

corpus callosum and around the posterior surface of the thalamus. The two crura now converge to form the body of the fornix, which is applied closely to

the undersurface of the corpus callosum. As the two crura come together, they are connected by transverse fibers called the commissure of the fornix. These fibers decussate and join the hippocampi of the two sides.

Anteriorly, the body of the fornix is connected to the undersurface of the corpus callosum by the septum pellucidum. Inferiorly, the body of the fornix is related to the tela choroidea and the ependymal roof of the third ventricle.

The body of the fornix splits anteriorly into two anterior columns of the fornix, each of which curves anteriorly and inferiorly over the interventricular foramen (foramen of Monro). Then, each column disappears into the lateral wall of the third ventricle to reach the mammillary body.

Stria terminalis It is the efferent fibers of the amygdaloid body It runs in the roof of the inferior horn of lateral ventricle then it follow the

curve of the caudate nucleus it runs in the groove between the caudate nucleus and the thalamus with the thalamostriate vein

It projects to: septal area, hypothalamus, anterior thalamic nuclei and habenular nucleus

Stria medullaris thalami It connects the septal area with the habenular nucleus

Medial forebrain bundle It connects the septal area with the hyopthalamus

Mamillothalamic tract It connects the mamillary body with the anterior nucleus of the thalamus

The cingulum It is a fiber bundle that connect the cingulate gyrus to the parahippocampal gyrus

The classic Papez circuit for emotions (1937) comprises of;

hippocampus → fornix → mammillary body → mammillothalamic tract → anterior thalamic nuclear group → cingulate gyrus → parahippocampal gyrus and neural linkages back to the hippocampus