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Smells are surer than
sounds and sights to
make your heart-strings
crack.
- Rudyard Kipling
Olfactory system

Conveys specific visceral sensation (smell) via
n. olfactorius.

Does not relay in the thalamus.

Connections with thalamus, hypothalamus,
amygdaloid complex & hippocampal formation.
Structure of the olfactory system
І. Receptor cells

Chemoreceptors.

Aboutо 25 billions on each side.

Located in the nasal mucosa.

Regenerate.

1st order neurons in the olfactory pathway.

Bipolar neurons, unmyelynated axons form nn.
оlfactоrii.

In bulbus olfactorius the axons synapse with the
mitral cells in olfactory glomerulus.
Nervi olfactorii
II. Bulbus olfactorius




On lamina cribrosa of os ethmoidale
Entered by olfactory nerves.
6-layered structure.
4 cell types:
–
–
–
–

periglomerular - inhibitory
tufted - efferent (ІІ order)
mitral - efferent (ІІ order)
granule - inhibitory
Glomerulus – polysynaptic structure, ensuring
conversion of olfactory impulses on the mitral cells.
Bulbus olfactorius
Bulbus olfactorius -клетъчен състав
Synaptic organization of
bulbus olfactorius
Dendrodendrite
synapses
Glutamate (excitory)
GABA (inhibitory)
Types of synapses
Lateral inhibition.
ІІІ. Tractus olfactorius:
–
–
–
–
in sulcus olfactorius.
Axons of mitral and tufted cells.
nucl. olfactorius anterior (modulator):
terminates in trigonum olfactorium.
ІV. Stria olfactoria lateralis
– to primary olfactory cortex through limen insulae
V. Stria olfactoria medialis
– to area subcalosa and gyrus paraterminalis
Tractus olfactorius
VІ. Olfactory corex

Primary
–
–
–
–

on uncus (area 34 after Brodmann).
fibers from stria olfactoria lateralis.
contains prepiriform & periamygdaloid areas.
connectins with nucl. medialis dorsalis of thalamus,
hypothalamus, hipocampal formation.
Secondary
– entorhinal area of gyrus parahippocampalis (area 28).
– Impulses from primary areas.
– efferents to hippocampus.

Orbitofrontal cortex
– Impulses from nucl. medialis dorsalis thalami
– conscious preception of smell.
Olfactory corex
Orbitofrontal cortex
We need our orbitofrontal cortex to make intelligent
choices. Its individual cells code for value.
Ann Thomson, Nature Neuroscience
Pathways in the olfactory system
Limbic system
Limbic system

Morphological substrate of emotions and behaviour.

Role in emotional behavior, feeding, defensive
reaction, sexual behaviour, memory and learning.

Functions mediated through hypothalamus and
autonomic system.

Contains cortical & subcortical (nuclei) structures.
Affective
behavior
Emotion
Happiness
and
Grief
Introduction
Concept
Broca (1877) - ‘La Grand Lobe Limbique’
Papez (1937) - ‘Limbic Circuit’ - emotion
MacLean (1952) - ‘Limbic System’ – visceral brain
Nauta (1972) - ‘Septo-hypothalamo-mesencephalic continuum’
PAUL BROCA
(1824-1880)
JAMES PAPEZ
(1883-1958)
Limbic system
- Term of Paul MacLean (1952)
- Visceral brain
-Triple concept
of brain evolution
Hypothalamus
Nucleus accumbens
Nucleus amygdaloideus
Cortex orbitofrontalis
Some psychiatric implications on
physiological studies on frontotemporal portions of limbic system
(visceral brain). Electroencephalogr
Clin Neurophysiol 4: 407-418, 1952
Paul D. MacLean (1913- )
Parts of the limbic system
Olfactory
cortex
Septo-(Preoptico)-Hypothalamo- Mesencephalic Continuum
Hippocampal
formation
Area
septalis
Midbrain
Hypothalamus
Amygdaloid
complex
Limbic system
Spinal
cord
&
Brain
stem
Expression of
emotion
Septohypothalamo-
mesencephalic
continuum
Parts of the limbic system
TELENCEPHALON
Lobus Limbicus
Gyrus Fornicatus
Gyrus Cingulatus
Gyrus Parahippocampalis
Hippocampal Formation
Hippocampus
Gyrus Dentatus
Subiculum
Hippocampal Rudiments
Gyrus Fasciolaris
Indusium Griseum
Cortex Olfactorius (Rhinencephalon)
- Lobus Piriformis
Cortex Prepiriformis
Cortex Periamygdaloideus
Cortex Entorhinalis
Basal forebrain
Substantia Innominata
Nucleus Basalis на Meynert
Pallidum Ventralis
Nucleus Accumbens (Septi)
Regio Septalis
Area Septalis
Gyrus Paraterminalis
Gyrus Subcallosus
Nuclei Septalis
Dorsal, lateral and medial
Nuclei Septalis
Nucleus Stria Diagonalis Broca
Nucleus Stria Terminalis
Corpus Amygdaloideum
Pars Corticomedialis
Pars Basolateralis
Nucleus Centralis
Lobus Limbicus
Lobus Limbicus
Gyrus Fornicatus
Gyrus Cinguli
Gyrus Parahippocampalis
Area Entorhinalis
Isthmus
Hippocampal Formation
Hippocampus Proper
(Ammon’s horn)
Gyrus Dentatus
Subiculum
Hippocampal Rudiments
Gyrus Fasciolaris
Indusium Griseum
Класификация на кората
Isocortex - Neocortex
Allocortex
Archicortex
Hippocampus
Gyrus Dentatus
Paleocortex
Bulbus Olfactorius
Lobus Piriformis
Mesocortex (Juxtallocortex,
Periallocortex, Mesallocortex)
Gyrus Cinguli
Parts of the limbic system
Limbic cortex

On medial aspect of the hemispheres

Archicortex
– In some parts paleo- & neocortex.

External ring

Internal ring
Limbic cortex
External ring
- gyrus cinguli
- area subcallosa
- gyrus parahippocampalis
- uncus.
Internal ring
- gyrus paraterminalis
- indusium griseum
- Hippocampal formation.
Hippocampal formation
Hippocampus Proper
(Ammon’s horn,
Cornu Ammonis)
Gyrus Dentatus
Subiculum
Hippocampal formation
Hippocampus – cortical fold in the lateral
ventricle caused by sulcus hippocampi
- 3-layered archicortex
- stratum pyramidale - efferents, forming
alveus and fimbria hippocampi
- stratum moleculare
- stratum radiatum
-
Subiculum (paleocortex)
- affrents from hippocampus
- efferents to corpora mamillaria and
nucl. anterior thalami
Parasubiculum (paleocortex)
- transition to gyr. parahippocampalis
Hippocampal formation
1. uncus
2. gyrus dentatus
3. fornix
4. corpus callosum
5. gyrus fasciolaris
6. sulcus
hippocampalis
7. gyrus
parahippocampal
8. sulcus collateralis
Hippocampal formation (lateral view)
Hippocampal formation (medial view)
Hippocampal formation - Archicortex
Archicortex - 3 layers
Hippocampus Proper
Str. Moleculare
Str. Pyramidale
Str. Polymorphe
Gyrus Dentatus
Str. Moleculare
Str. Granulare
Str. Polymorphe
Subiculum
Transient between hippocampal archicortex and entorhinal paleocortex
Classification of the cortex
Isocortex
6-layered cortex
homotypical and
heterotypical
Allocortex
Paleocortex
olfactory cortex
- lobus piriformis
Archicortex
3-layered
- hippocampal formation
Archicortex - after Ramon y Cajal
7. stratum
moleculare
6. stratum
lacunosum
5. stratum
radiatum
4. stratum
pyramidalis
3. stratum oriens
2. alveus
1. ependyma
Hippocampus and memory
Х.M. - пациент с антеградна и
ретроградна амнезия,
възникнала след мозъчна
операция за лечение на
епилептични припадъци.
Connection in the hippocampal formation
1. Internal connections
trisynaptic pathway
2. Afferent connections
perforant and alveolar pathway
3. Efferent connctions
fornix
Internal connections
Classical 3-neuron pathway
1. Енторинална кора (perforant pathway)
 granule cell of gyrus dentatus
2. Granules cells (mossy fiber)
 CA3 pyramid cells
3. Pyramid cells (Schaffer collateral)
 CA1 pyramid cells
 subiculum  cortex entorhinalis
Afferents
From Cortex Entorhinalis
Alveolar pathway
from medial EC
to CA1 and Subiculum
Perforant pathway
from medial EC
to CA1, CA2, CA3 &
Gyrus Dentatus
Efferents
FORNIX
Alveus
Fimbriae
Crus
Commissurа
Corpus
Column
Efferents
Fornix
- from pyramid cells of hippocampus & subiculum
- 1.2 million fibers
Postcommissiral Fornix – basic bundle
to Corpus Mammillare
Thalamus Anterior
Nuclei Septi Lateralis
Hypothalamus
Tegmentum of midbrain
Efferents
Precommissural Fornix – smaller
- mainly from hippocampus proper
to Nuclei Septi
Area Preoptica Lateralis
Area Hypothalamica Anterior
Nucleus Striae Diagonalis Broca
Nucleus Accumbens
Medial aspect of frontal lobe
Nucleus Caudatus & Putamen
Amygdala & Claustrum
Summary of connections
Afferent
Entorhinal Cortex
Alveolar pathway
medial EC
to CA1 and Subiculum
Perforant pathway
from lateral EC
to CA1, CA2, CA3 and
GyrusDentatus
Gyrus Dentatuse
Mossy fiber - CA3
- Schaefer fiber (CA3-CA1)
Others
Hypothalamus, Nuclei Septi,
Substantia Innominata
Midbrain
Efferent
FORNIX
from pyramid cells
hippocampus & subiculum
Alveus, Fimbriae, Crus
Commissure, Corpus, Column
Precommissural Fornix
to Nuclei Septal,
Nucleus Accumbens
Area Hypothalamica Anterior
Nucleus Olfactorius Anterior
Postcommissural Fornix
to Corpus Mammillare
Thalamus Anterior
Hypothalamus
Nucleus Striaе Terminalis
Subcortical limbic structures
1. Amygdaloid complex
2. Mammillary body
3. Septal area
4. Nucleus anterior, nucleus medialis dorsalis &
nuclei intralaminares thalami
5. Nucleus accumbems
6. Substantia innominata
7. Nuclei habenulae
8. Hypothalamus
9. Midbrain limbic nuclei
Amygdala
L. almond
K. F. Burdach’s
term
Amygdaloid complex
Amygdaloid complex

Within uncus

Process sensory information

Determines emotional level, especially negative

Modulates affective expression

Autonomic, endocrine and affective reactions
– Aggression when stimulated
– Calm, fearless in damage
Amygdaloid complex
А. Corticomedial part
B. Basolateral part
C. Connections
- Stria terminalis
- Ventral amygdalofugal pathway
Connections of the Amygdala
Amygdaloid Nuclear Complex
Emotion
& Amygdala
Autism
Dysfunction of
amygdala
Mercury
Rising
Limbic subcortical nuclei (cont.)
Area septalis
Septum precommissurale
Nucleus tractus diagonalis
(Broca)
Septum pellucidum
Nuclei septi pellucidi
Conections
Corpus amygdaloideum (stria terminalis)
Habenula (stria medullaris)
Corpus amygdaloideum, hippocampus (diagonal band of Брока)
Orbitofrontal cortex, hypothalamus, midbrain (medial forebrain bundle)
Nucleus basalis of Meynart
-
above substantia perforata anterior
-
Large cholinergic neurons
-
Afferents fron olfactory and limbic
structures
-
Duffuse cortical projections
Damaged in cortical dementia
(Alzhaeimer disease)
Nucleus accumbens. Center of pleasure
- ventral striatum
- Connection between limbic and extrapyramid system
- Regulates processes of reward, motivation and addiction. Cocain and
nicotine cause release of dopamin from its cotical part.
Pathways
1. Fornix
2. Stria terminalis
3. Ventral amygdalofugal pathway
4. Stria medullaris thalami
5. Diagonal band of Broca
6. Fasciculus retroflexus
Limbic circuit of Papez
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