The limbic system is located at the border of the cerebral cortex and diencephalon. It consists of grey matter structures like the hippocampus, amygdala, hypothalamus, and white matter tracts connecting these structures. The limbic system is involved in functions like emotion, learning, memory formation and processing. Key structures include the hippocampus, which is important for memory consolidation, and the amygdala, which is involved in processing fear and other emotions. The reticular formation is located in the brainstem and consists of nuclei that regulate states of consciousness through ascending and descending pathways.

2. Limbic system
• “Limbic“ from Latin word Limbus
• Means "border" or "edge".
• Separates
• Medial surface of cerebral cortex
• From diencephalon
• Consists of
• Grey matter
• Cortical structures
• Subcortical structures
• White matter
• Interconnecting fibre tracts

3. Grey matter
• Limbic lobe
• Hippocampal formation
• Amygdala
• Hypothalamus
• Thalamus
• Septal area
• Habenular nuclei (epithalamus)

4. Limbic lobe
• C-shaped ring of grey matter
– On medial surface of each cerebral
hemisphere
• Surrounding the corpus callosum
– 1. Subcallosal area
– 2. Cingulate gyrus
– 3. Isthmus
– 4. Parahippocampal gyrus
– 5. Uncus

5. Subcallosal gyrus
• A narrow lamina of grey matter
• Lies
• Infront of lamina terminalis
• Behind the parolfactory area

6. Cingulate gyrus
• Lies dorsal to
• Corpus callosum
• Receives inputs from
• Anterior nucleus of thalamus
• Projects to
• Entorhinal cortex via cingulum
• Involved with
• Emotion formation and processing,
learning, and memory
• Lesions lead to
• Akinesia, mutism

7. Parahippocampal gyrus
Parahippocampus
• Lies in medial temporal lobe
• Medial to collateral sulcus
• Important role
• In memory encoding and retrieval
• ERC
• Funnels highly processed cortical
information
• To hippocampal formation and serves
as its major output pathway

8. Uncus
• 2 parts by tail of dentate gyrus
• Uncinate gyrus
• Intralimbic gyrus

9. Hippocampal formation
Hippocampus
Dentate gyrus
Gyrus
fasciolaris
• Hippocampus
• Dentate gyrus
• (Which lies medial to hippocampus)
• Gyrus fasciolaris
• Indusium griseum
Cingulate gyrus
Indusium griseum

10. Hippocampus
• Consolidation of new memories
• Lies in
• Floor & medial wall of
• Inferior horn of lateral ventricle
Called as cornu ammonis
Ancient Egyptian deity,
Ammon
nferior horn of
Lateral ventricle

11. Hippocampus
• The most sensitive
area in brain
• For Ischemic events
in hippocampus is
CA1
• Trilaminate structure
• Molecular
• Pyramidal
• Polymorphic

12. Dentate gyrus
• Longitudinal strip of grey matter
• Lies
• Medial to hippocampus
• Fused with hippocampus
• On its lateral margin
• Medial margin is crenated
Dentate
gyrus

13. Dentate gyrus
• Anteriorly it ends as tail
• Runs across the inferior
surface of uncus
• By that uncus is divided
into
• Anterior uncinated
gyrus
• Posterior intralimbic
gyrus
• Posteriorly it continues
as
• Gyrus fasciolaris

14. Gyrus fasciolaris & Indusium griseum
• Gyrus fasciolaris
• Continuation of dentate gyrus
• Indusium griseum
• Grey matter on upper surface of
corpus callosum
• Contains 2 longitudinal bands
• Medial & lateral longitudinal striae
• Anteriorly ends in paraterminal
gyrus
• Infront of lamina terminalis
Gyrus
fasciolaris
Indusium griseum
Paraterminal gyrus

15. Subiculam
• Transitional zone
• Between
• Six layered
• Entorhinal cortex and
• Three layered
• Hippocampus

16. Subcortical nuclei
• Amygdaloid complex
• Septal region
• Olfactory areas
• Hypothalamus
• Anterior nucleus of
thalamus
Anterior nucleus of thalamus
Hypothalamus
Septal
Amygdaloid

17. Amygdala
• Site
• In temporal pole
• Lies deep to uncus
• Function
• Fear
• Emotions
• Anger
• Hormonal secretions

18. Paraterminal gyrus
• Lies infront of lamina terminalis
• 2 gyri
• Para terminal gyrus
• Parolfactory gyrus
• Continues inferiorly
• With diagonal band & medial olfactory
stria
• Continues superiorly
• With indusium griseum
Septal area
Pleasure zone

19. Piriform
• 3 parts
• Prepiriform region
• Lateral olfactory gyrus
• Gyrus ambiens
• Gyrus seminularis
• Entorhinal area
• Uncus + parahippocampal gyrus
(anterior part)

20. Hypothalamus
– Lies
– Anteroinferior to thalamus
• Mammilary bodies
• Contains ANS nuclei

21. Thalamus
• Anterior nucleus of thalamus

22. Fibres of limbic system
• Stria terminalis
• Fornix
• Mamillo thalamic tract
• Stria medullaris thalami
• Cingulum

23. Stria terminalis
• Begins in
• Amygdaloid complex
• Runs
• Backwards in the roof of inferior
horn
• Terminates near
• Interventricular foramen
• and anterior commissure by
dividing into various bundle
• To
• Hypothalamus & septal area
Amygdaloid body
Stria terminalis
Anterior commissure

24. Fornix
• Formation
– Axons of hippocampus is called
alveus
• Parts
– Fimbria (flat over dentate gyrus)
– Crus (when it becomes rounded)
• Arches upwards & forwards underneath
splenium
– Body
• Crura curving over thalamus converge
• Lies beneath trunk of corpus of
callosum
– Column
• Arches downwards towards anterior
commissure
• Curves posteriorly to end in mamillary
body
• Post commissural fornix
• Precommissural fornix
C-shaped group of fibers
connecting
hippocampus with mammillary body

25. Mammillothalamic tract
• Carry the impulses
• From
• Mammillary body
• To
• Anterior nucleus of thalamus
Mammillothalamic tract
Anterior nucleus of thalamus

26. Stria medullaris thalami
• From
• Septal area
• To
• Habenular nuclei
(amygdala and hippocampus)

27. Medial forebrain bundle
• Consists of
• Ascending & descending fibres of
hypothalamus
• Ascending fibres
• From midbrain
• To hypothalamus
• Descending fibres
• From orbitofrontal cortex
• Septal area, olfactory tubercle & piriform
cortex
• To hypothalamus (lateral hypothalamic
zone & preoptic nuclei)

28. Cingulum
• Connecting cingulate gyrus
to hippocampus
• Association fibres

29. Applied anatomy
• Korsakoff’s syndrome
• Loss of recent memory
• Results from deficiency of thiamine
(vitamin B1)
• Leads to damage to mammillary bodies
and dorsomedial nucleus of thalamus
• Temporal lobe epilepsy
• Temporal lobe can be damaged
• Through chronic seizures
• Herpes encephalitis
• Kluver-Bucy syndrome
• Bilateral ablation of amygdaloid
• Hyperphagia & hyper sex

30. Functions
• Olfaction
• Olfactory tract divides into lateral,
intermediate and medial stria
• Lateral stria
• Terminate in primary olfactory cortex of the
uncus
• Some fibres
• To hippocampal gyrus – Memory of smell
• To amygdala – Emotion of smell

32. Functions – Memory / Learning
• Papez circuit (James Papez, 1937)
• Storing memory
• Learning

33. Function – Emotions & behaviours
• Emotion
• Any stimulus produces fear, anger, rage
or sadness
• Without conscious awareness
• Due to increased activity in amygdala

34. Functions - Feeding

35. Reticular Nuclei
• Location
• Brainstem – Tegmentum
• Arrangement
• Three columns
• Median column
• Medial column
• Lateral column

36. Median column
• Lie
• In mid line
• From medulla to
midbrain
• Nuclei
• Nuclei of Raphe

37. Medial column
• Lie
• Lateral to nuclei of
median column
• Nuclei
• Neurons are large in size
• So column can be named
as
• Magnocellular column
• Giganto cellular nucleus
• Pontine tegmental
reticular nucleus
• Cuneiform and sub
cuneiform nuclei

38. Lateral Column
• Lie
• Lateral to medial column
• Nuclei
• Made up of small cells
• This column is known as
Parvocellular column
• Control mainly the
visceral functions

39. Functional divisions
• On the basis of functions
• Two systems namely
• Ascending reticular activating system
• Descending reticular activating system

40. Ascending reticular activating system
• Responsible for maintaining
• Alertness & consciousness
• Most of the ascending tracts
passing through brain stem
• Gives collaterals to lateral part of
reticular formation
• From lateral part of reticular formation
to intralaminar & reticular nuclei of
thalamus
• From these nuclei fibres project to
cerebrum

41. Descending reticular system
• Has
• Descending pathways from reticular
formation to
• Autonomic centres in brain stem
• Lateral & anterior horns of spinal cord