1

Limbic systemBy Prof. Adel Abdel Aziz

It is formed of groups of nuclei connected together by fiber bundles.

Nuclei of the limbic system:1. Limbic lobe: formed of the cingulated gyrus, parahippocampal gyrus and the uncus.2. Hippocampus: is continuous externally with the parahippocampal gyrus.3. Hypothalamus: especially the mamillary bodies.4. Thalamic nuclei: anterior and medial nuclei.5. The prefrontal cortex (the personality center).6. Amygdaloid nucleus.7. Septal area (medial olfactory area): below the rostrum.8. Habenular nucleus.

2

Cingulate gyrusBody of fornix

Lingual gyrus

Isthmus of cingulate gyrus

Column of fornix

Uncus

Collateral sulcus

Parahippocampal gyrus

Crus of fornix

Fimbria

Dentate gyrus

Splenium

3

Uncus

Parahippocampal gyrus

Isthmus of cingulate gyrus

Lingual gyrus

Splenium

Collateral sulcus

4

Fiber bundles of limbic system

1. Fornix: it arises from the hippocampus and terminates in the mamillary body. The fornix is formed of 4 parts:

a. Fimbria: is the continuation of alveus which is formed of axons of the neurons of the hippocampus and passes along its medial border.

b. Crus of the fornix: is the continuation of the fimbria below the splenium.

c. Body of the fornix: the two crura fuse to form the body of the fornix.

d. Anterior column of the fornix: each one terminates in the mamillary body.2. Cingulum: is the fiber bundle of the limbic lobe.3. Mamillothalamic tract: connects the mamillary body with the anterior thalamic nucleus.4. Stria terminalis: it begins in the septal area and in the habenular nucleus.

5

Pes hippocampus

Dentate gyrus

Hippocampus

Fimbria

Columns of fornix

Corpus callosum

Head of caudate

Septum pellucidum

Collateral trigone

Thalamus

6

Anterior column of fornix

Body of fornix

Crus of fornix

Pes hippocampus

Hippocampus

Fimbria

Dentate gyrus

Splenium

Stria terminalis

Inf. horn of lat. vent.

Commissure of fornix

Head of caudate

Corpus callosum

Thalamus

7

Anteriorfornix

fornix

8

Connections

Afferent connections:

1. Fibers arise from the cingulated gyrus pass to the hippocampus.2. Fibers from hippocampus of one side pass to hippocampus of the

other side along the fornix.3. Fibers arise from the parahippocampal and dentate gyri pass to

hippocampus.4. Fibers arise from the olfactory association cortex pass to the

hippocampus.

Efferent connections:The fibers of the fornix are distributed to:1. Fibers pass to the anterior commissure to the mamillary body and

anterior part of hypothalamus.2. Fibers pass to the anterior commissure to end in the anterior nuclei of

thalamus.3. Fibers pass to the anterior commissure to enter the tegmentum of the

midbrain.4. Fibers join the habenular nuclei.

9

Functions of the limbic system1. Recent memory: the hippocampus plays a role in remembering the recent events.2. Emotional behavior: it plays a role in anger, fear, and emotional behavior associated with sexual behavior.

Malfunction of the limbic systemThe malfunction is involved in psychiatric disorder, including schizophrenia, depression, and senile dementia. Antipsychotic drugs block limbic dopamine receptors.

Lesions1. Lesion in the hippocampus causes loss of the recent memory.2. In Alzheimer's disease, there is extensive degeneration in the hippocampus.3. Lesions in the amygdaloid nucleus cause loss of the aggressive behavior, fear and anger.

10

PartFunction

AmygdalaAGGRESSION and FEAR

Cingulate gyrusAUTONOMIC FUNCTION

HippocampusRECENT MEMORY

HypothalamusENDOCRINE FUNCTION

Mammillary bodyLONG MEMORY

Nucleus accumbensADDICTION

Prefrontal areaPERSONALITY

ParahippocampusSPATIAL MEMORY

11

• Degenerative disease of the brain of unknown cause.• Diffuse atrophy of cerebral cortex.• Middle to late life.• Genetic predisposition.• Senile Plaques.• Manifestations include:

complete disorientation. deterioration of speech. restlessness.Loss of RECENT MEMORY (HIPPOCAMPUS)

12