THE LIMBIC SYSTEM

DR.SWATI PATIL

LIMBIC SYSTEM

• Introduction• Anatomical structures• Connecting pathways• Functions• Applied

INTRODUCTION• Broca –great limbic lobe• Papez –circuit of Papez• Paul D. Maclean –

reintroduced term limbic

• Kluver Bucy –temporal lobectomy –Extreme behavioral syndrome –Kluver Bucy syndrome

Paul D. MacLean

FUNCTIONS OF LIMBIC SYSTEM

• Integration of olfactory, visceral, somatic impulses

• Control of activities necessary for survival of animal

• Control of activities necessary survival of species

• Emotional behaviour• Retention of recent memory

Cortical & Subcortical Limbic Areas

COMPONENTS OF LIMBIC SYSTEM • Limbic lobe• Hippocampal formation• Amygdaloid body• Connecting pathways

LIMBIC SYSTEM

OVERVIEW OF LIMBIC STRUCTURE

HIPPOCAMPAL FORMATION

• Hippocampus proper• Dentate gyrus• Subicular complex• Entorhinal area

HIPPOCAMPUS

• Cornu ammonis• Location :-• Pes hippocampi• Alveus • Fimbria

HIPPOCAMPUS

HIPPOCAMPUS

• Trilaminar archicortex :--3 distinct fields :-CA1,CA2,CA3

• CA3:- largest Pyramidal cells - receive mossy fibres• CA2 :-pyramidal cells -input from supramammillary

region• CA1 :-most complex

• Strata within layers of hippocampus :-

- Stratum oriens- Stratum pyramidalis- Stratum radiatum- Stratum lacunosum• Schaffer’s collaterals• Perforant pathway

DENTATE GYRUS

• Crenated strip of cortex• Beaded/ toothed

surface• Fimbriodentate sulcus• Gyrus fasciolaris& indusium griseum

LIMBIC SYSTEM

[

• Cotrex of dentate gyrus-granule cell

layer(principal cells)-molecular cell layer-polymorphic layer

• Mossy fibres• Fascia dentata

SUBICULAR COMPLEX

• Subicular complex :-• Trilaminar archicortex-molecular layer -pyramidal layer:-major

subcortical projections-polymorphic layer

ENTORHINAL CORTEX(Brodmann’s area no 28)

• Location :-• Receive projections

from olfactory bulb• Layer 1-6:-

FORNIX & FIMBRIA

• FimbriaOf hippocampus• Crus of fornix : ->1

million fibres -afferent and efferents• Columns of fornix

HIPPOCAPMAL COMPLEX: CIRCUITARY

• Excitatory pathways-perforant pathway-mossy fibres-schaffer’s collaterals

• Inhibitory pathways-GABA neurons in denatate

gyrus

AFFERENT CONNECTIONS

1. Cerebral neocortex2. Septal area3. c/l hippocampus4. Nuclei in reticular

formation of brain stem

• Entorhinal area :-follow 2 routes to hippocampus

-Perforant path-Alveolar path

• Fornix and fimbria :-fibres come from C/L hippocampus

-thalamic and hypothalamic nuclei

-ventral tegmental nuclei-locus ceruleus-raphe nuclei

EFFERENT CONNECTIONS• Efferents – same cortex - diencephalon - brain stem• Fornix :-largest efferents-originate in subiculum,

hippocampus-Alveus – fimbria – crus of

fornix – body of fornix• Parahippocampal gyrus –

dorsal hippocampal commissure –hippocampal formation

EFFERENTS

• Columns of fonix- septal area, ant part of hypothalamus, substantia innominata

• Lateral dorsal thalamic nucleus – thalamus – mamillary body – ant nucleus of thalamus

• Mamillotegmental fasciculus

PAPEZ CIRCUIT

• The circuit of Papez• Ring of

interconnected neurons

• Input to circuit• Output to circuit• Mamillotegmental

fasciculus

FUNCTIONS OF HIPPOCAMPUS• Retention of short term

memory – long term declarative memory

LIMBIC SYSTEM STRUCTURE

AMYGDALA

• Almond• Involved in Central

regulation of ANS connection to hypothalamus

• Controls survival fight-or-flight response of ANS

• Emotional & visceral responses

AMYGDALA

• Several group of nucleus• B/w inferior horn of lateral

ventricle & lentiform nucleus

• Two divisions :- -dorsomedial -ventrolateral – Basolateral - central

AFFERENTS OF AMYGDALA

• Reciprocal connections • Subcortical afferents • Dopaminergic afferents –

ventral tegmental area• Cholinergic afferents –

basal forebrain nuclei• Olfactory corticomedial &

non olfactory basolateral nuclei – central nuclei

EFFERENTS OF AMYGDALA• Stria terminalis – septal

area, preoptic area, anterior hypothalamus

• Medial forebrain bundle – brain stem

• Ventral amygdalofugal pathway – diagonal band of broca – septal area – nucleus accumbens – dorsomedial nucleus of thalamus – prefrontal cortex

• Septal area – stria medullaris thalami – habenular nuclei – reticular formation – autonomic nuclei

Amygdala Connections

Cerebral cortexOlfactory system

ThalamusBrainstem reticular formation

Hypothalamus

AMYGDALA

Striaterminalis

Ventral Amygdalofugalfibers

FUNCTIONS OF AMYGDALA

• Central and basolateral nuclei of amygdala – behavioral and emotional functions

• Emotional responses• Electric stimulation – feeling of fear, general

irritability, anger• Behavioral and cognitive disturbances

APPLIED

• Kluver Bucy syndrome

-complete removal of both temporal lobes

-amygdaloid body, hippocampal formation

-docility, lack of emotional responses, increased sexual activity (perverted), visual agnosia

-Amygdaloid body lesion-Lesion of hippocampi

• Anxiety states-Inappropriate activity of amygdala-Panic attacks of excessive activity of sympathetic

nervous system, subjective feeling of worry-Treatment – anxiolytic drugs

• Schizophrenia-anatomical measurements reduced in size-antipsychotics antagonise action of dopamine-parkinsonism-tardive dyskinesia

• Memory disorders-consolidation of new short term memory-arterial occlusion – infarction – loss of hippocampal

function-transient global amnesia-head injury –damage to hippocampus – hemorrhage –

anterograde amnesia

- B/l hippocampal lesion – major circuit of hippocampus- B/l transaction of fornix – severe amnesia

• Alzheimer’s disease –- loss of cholinergic neurons of substantia innominata

which project to hippocampus -ass. with degenerative changes in entorhinal cortex,

hippocampus, extensive neocortical atrophy-amnesia for recently occurred events as mechanism for

retention of new memory not operating