The Olfactory System (Rhinencephalon) & The Limbic System Flashcards
1
Q
What does the Olfactory System do?
A
- conveys specific visceral sensation (smell) via olfactory nerve
- Does not relay in the thalamus.
- Connections with thalamus, hypothalamus, amygdaloid complex & hippocampal formation
2
Q
What is the structure of the olfactory system?
A
- Chemoreceptors - About 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
3
Q
Where is the Olfactory Nerve located?
A
- first CN
4
Q
What is the Olfactory Bulb?
A
is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell
- It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OFC) and the hippocampus where it plays a role in emotion, memory and learning
5
Q
Structure of the Olfactory bulb
A
On lamina cribrosa of ethmoid bone
- 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 impulseson the mitral cells.
6
Q
Synaptic Organisation of olfactory bulb
A
7
Q
Types of Synapses on olfactory bulb
A
- lateral inhibition
8
Q
Olfactory tract
A
- bilateral bundle of afferent nerve fibers from the mitral and tufted cells of the olfactory bulb that connects to several target regions in the brain, including the piriform cortex, amygdala, and entorhinal cortex
- It lies in the olfactory sulcus on the inferior surface of the frontal lobe
- anterior olfactory nucleus - modulator, supposedly strong influence on other olfactory areas like the olfactory bulb
- terminates in trigonum olfactorium
9
Q
medial olfactory stria of olfactory tact
A
- turns medially behind the parolfactory area and ends in the subcallosal gyrus
10
Q
lateral olfactory stria of olfactory tract
A
is directed across the lateral part of the anterior perforated substance and then bends abruptly medially toward the uncus of the parahippocampal gyrus
- to primary olfactory cortex through limen insulae
11
Q
Describe the Olfactory Cortex
A
The uncus houses the olfactory cortex which includes the piriform cortex (posterior orbitofrontal cortex), amygdala, olfactory tubercle, and parahippocampal gyrus
- has fibers from lateral olfactory stria
- contains prepiriform & periamygdaloid areas.
- connections with nucl. medialis dorsalis of thalamus, hypothalamus, hipocampal formation
- primary
12
Q
Secondary Olfactory Cortex
A
- entorhinal area of gyrus parahippocampalis (area28).
- Impulses from primary areas.
- efferents to hippocampus
13
Q
Orbitofrontal cortex of olfactory cortex
A
- Impulses from nucl. medialis dorsalis thalami
- conscious preception of smell
14
Q
Pathways in the olfactory system
A
15
Q
What is the Limbic System
A
- complex set of structures that lies on both sides of the thalamus, just under the cerebrum. It includes the hypothalamus, the hippocampus, the amygdala, and several other nearby areas
- medial asepect of hemispheres
- archicortex, external and internal ring
- 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
16
Q
Limbic system term by Paul Maclean
A
- visceral brain
- triple concept of brain evolution
Hypothalamus
Nucleus accumbens
Nucleus amygdaloideus
orbitofrontal cortex
17
Q
Parts & Connections of the limbic system
A
18
Q
List of parts of the limbic system
A
19
Q
What is the limbic lobe
A
- an arc-shaped region of cortex on the medial surface of each cerebral hemisphere of the mammalian brain, consisting of parts of the frontal, parietal and temporal lobes
- including the paraterminal gyrus, the subcallosal area, the cingulate gyrus, the parahippocampal gyrus, the dentate gyrus, the hippocampus and the subiculum
- others include the cingulate sulcus, the cingulate gyrus, the isthmus of cingulate gyrus, the fasciolar gyrus, the parahippocampal gyrus, the parahippocampal sulcus, the dentate gyrus, the fimbrodentate sulcus, the fimbria of hippocampus, the collateral sulcus, and the rhinal sulcus, and omits the hippocampus.
- 5-7
20
Q
External ring of limbic cortex
A
21
Q
Internal ring of limbic cortex
A
- paraterminal gyrus (subcallosal)
- indusium griseum
- hippocampal formation
22
Q
Hippocampal formation
A
- compound structure in the medial temporal lobe of the brain
- thought to play a role in memory, spatial navigation and control of attention
- the dentate gyrus, the hippocampus proper and the subiculum
23
Q
Describe the Hippocampus
A
- Humans and other mammals have two hippocampi, one in each side of the brain
- 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
24
Q
Subiculum (paleocortex) & Parasubiculum (paleo-) of hippocampal formation
A
affrents from hippocampus
- efferents to mammillary body and nucl. anterior thalami
Para-
- transition to gyr. parahippocampalis
25
Describe the 3 layers of the hippocampal formation (archicortex)
**Hippocampus Proper**
Str. Moleculare
Str. Pyramidale
Str. Polymorphe
**Gyrus Dentatus**
Str. Moleculare
Str. Granulare
Str. Polymorphe
**Subiculum**
Transient between hippocampal archicortex and entorhinal paleocortex
26
Classification of cortex
**Isocortex**
6-layered cortex
homotypical and heterotypical
**Allocortex**
- Paleocortex
olfactory cortex
- lobus piriformis
- Archicortex
3-layered
- hippocampal formation
27
Connections in hippocampal formation
1. Internal connections
trisynaptic pathway
2. Afferent connections
perforant and alveolar pathway
3. Efferent connctions
fornix
28
Internal connections of Hippocampal formation
- classic 3-neruon pathway
- perforant pathway --\> granule cell of gyrus dentatus
- granules cells (mossy fiber) --\> CA3 pyramid cells
- pyramid cells (schaffer collateral) --\> CA1 pyramid cells
- subiculum --\> cortex entorhinalis
29
Afferent connections of hippocampal formation
From Cortex Entorhinalis
Alveolar pathway - from medial EC to CA1 and Subiculum
Perforant pathway - from medial EC to CA1, CA2, CA3 and Gyrus Dentatus
30
Efferent connections of Hippocampal formation
fornix: C-shaped bundle of nerve fibers in the brain that acts as the major output tract of the hippocampus
- alveus fimbriae
- crus commissura
- corpus column
31
The posterior fibers (called the postcommissural fornix) of fornix
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
32
The anterior fibers (precommissural fornix) of fornix
end at the septal nuclei and nucleus accumbens of each half of the brain
- 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
33
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
34
Amygdala
- one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain in complex vertebrates
- role in the processing of memory, decision-making and emotional responses (including fear, anxiety, and aggression)
- the amygdalae are considered part of the limbic system
35
Amygdaloid Complex
- within the uncus
- processes sensory information
- determines emotional level, esp. -ve
- modulates affective expression
- autonomic, endocrine and affective reactions
- aggression when stimulated
- calm, fearless in damage
- corticomedial part, basolateral part and connections (stria terminalis and ventral amygdalofugal pathway)
36
Efferent Connections of the Amygdala
37
Dysfunction of Amygdala
Autism
38
Amygdala and Emotional Response
39
Amygdala and fear
40
Limbic subcortial nuclei
Septum Verum - Area septalis - region in the lower medial part of the telencephalon that separates the two cerebral hemispheres
## Footnote
Septum precommissurale - Nucleus tractus diagonalis (Broca)
Septum pellucidum - Nuclei septi pellucidi
Connections
Corpus amygdaloideum (stria terminalis)
Habenula (stria medullaris)
Corpus amygdaloideum, hippocampus
Orbitofrontal cortex, hypothalamus, midbrain (medial forebrain bundle)
41
Nucleus basalis of meynart
- subcortical structure
- mainly in the substantia innominata of the basal forebrain
- above substantia perforata anterior
- Large cholinergic neurons
- Afferents from olfactory and limbic structures
- Diffuse cortical projections
- Damaged in cortical dementia (Alzheimer's disease)
42
Nucleus accumbens
- center of pleasure
- ventral striatum
- Connection between limbic and extrapyramid system
- Regulates processes of reward, motivation and addiction
- Cocaine and nicotine cause release of dopamin from its cotical part
43
Pathways of Limbic System
1. Fornix
2. Stria terminalis
3. Ventral amygdalofugal pathway
4. Stria medullaris thalami
5. Diagonal band of Broca
6. Fasciculus retroflexus
44
Limbic circuit of Papez
neural circuit for the control of emotional expression
