Anatomical Components of Limbic system

Olfactory PathwayAmygdaloid complexHippocampal formationLimbic lobeSeptal nucleiHypothalamus

Mammillary bodiesAnt Nu ThalamusHabenular nuMid brain

Olfactory PathwayOlfactory

nervesBulbTractPyriform areaAnt perforated

subPara terminal

gyrus

The UncusIt is of clinical significance because:

1.Seizures often originate in this area ( uncinate fits). These seizures are often preceded by hallucinations of disagreeable odors.

2.When the volume of the temporal lobe is increased due to tumors, hemorrhage or edema, the uncus can press against the brainstem and cranial nerves with serious consequences( Uncal herniation). The herniating uncus and adjacent part of the parahippocampal gyrus push the brainstem to the opposite side, resulting in damage by pressure against the taut free margin of the tentorium cerebelli.

3.The brainstem damage is usually contralateral to the side of the herniation.

AnosmiaLoss of smell is term Anosmia.It is usually bilateral caused by common cold or allergic rhinitis.Unilateral anosmia could result from disease affecting the olfactory nerve, bulb or tract.A unilateral lesion can’t produce complete anosmia because of the bilaterality of the olfactory pathway.Fractures of the cribiform plate of ethmoid cause avulsion of the olfactory nerves.Cerebral tumors can produce anosmia by pressing on the olfactory bulb or tract.

Amygdaloid Complex

Amygdaloid ComplexThe amygdala is collections of nuclei Situated in the roof of the inferior horn

of lateral ventricleCortico-medial

Olfactory Baso-lateral

Parahippocampal gyrus

StriaterminalisIs the sole efferent of Amygdaloid complex

Supra commissuralSeptal nu

CommissuralVia ant comm opp amygdala

Sub commissuralPre optic and ant nu of hypothalamus

Function of Amygdaloid complexAgonistic behaviorAggressionFear Bilateral ablation of amygdala the animal

exhibits loss of aggressionDocileOccasional hypersexual behavior

Kluver- Bucy SyndromeBilateral damage to the rostro- ventral portion of the temporal lobes that includes the hippocampal formation, amygdala can lead to this syndrome.

a.Patients become Docile- previously violent patients displayed little or no emotion.

b.Anterograde amnesiac.Hyperphagiad.Hyperoralitye.Hypersexualityf. Visual Agnosia- patients do not recognize

complex visual patternsg.Psychic blindness- Objects in the visual field are

treated inappropriately.

Papez Circuit Papez Circuit Papez Circuit Papez Circuit

Hippocampal formationHippocampusDentate gyrus

Connections of hippocampus

Afferents 1. from cingulated gyrus via

cingulum2. from septal nuclei and

indusium griseum retracing through the fornix.

3. commissural fibers from the opposite hippocampus via the commissure of the fornix.

4. profuse connection from the entorhinal area.(para-hippocampal gyrus )

Efferents the fornix forms the sole

efferent projection fibers of the hippocampus

Fibres of dorsal fornix make synapses with the neurons of gyrus fasciolaris, indusium griseum, cingulated gyrus and reach the septal nuclei of septum pellucidum through the fibres of corpus callosum.

Pre-commissural fornix provides connections to the paraterminal gyrus, pre-optic and anterior hypothalamic nuclei.

Fibres of post commissural fornix terminate in the anterior nucleus of thalamus. Other hypothalamic nuclei mammailary body and reach hebenullar nucleus via stria medularis thalami.

Connections of the fornix.

Fear & Rage

Lesions of the HippocampusPeople with lesions of the temporal lobe including the Hippocampus can have a disruption of memory.This deficit is observed only when the damage is bilateral.bilateral. It can be sometimes noticed with unilateral lesions.This deficit is a loss of Recent memoriesa loss of Recent memories. This means that memory of recent events is lost. This is termed Anterograde AmnesiaAnterograde Amnesia.A common cause of bilateral Hippocampal damage is anoxia from interruption of blood or oxygen supply. The Hippocampus is one of the first sites to be irreversibly damaged by transient ischemia or anoxia.

Korsakoff's SyndromePatient with this syndrome also present with

Anterograde amnesia. Patients could also present with retrograde amnesia and confabulat( make up stories) to make up for past memories.

It is mainly seen in alcoholics who have thymine deficiency and follows an acute presentation of Wernicke’s Encephalopathy.

Wernicke’s Encephalopathy presents with Ocular palsies, confusion and gait ataxia. It is also related to Thymine deficiency.

In Wernicke- korsakoff Syndrome, lesion are always found in the mammillary bodies and the Dorsomedial nucleus of the Thalamus.

Septal AreaIt is a component of the limbic system located

anterior to the hypothalamus.It consists of the Septal nucleus, the septum

pellucidum, the small portion of the neocortex that forms part of the limbic lobe.

Because of it’s connections with the hippocampus and hypothalamus it is considered as part of the limbic system.

The hippocampus sends connections to the septal nuclei(area) by way of the columns of fornix.

Its function is not well understood.

Cingulate GyrusIs the portion of the limbic lobe that overlies

the corpus callosum.It receives connections from the anterior

nucleus of the thalamus. This puts it in close communication with the hypothalamus by way of the mammillothalamic tract.

The cingulate gyrus is connected to the parahipocampal gyrus by way of the cingulum.

It is believed to be involved in the generation of emotional and visceral responses but it is not quite clear how.