The Olfactory System (Rhinencephalon) & The Limbic System Flashcards
What does the Olfactory System do?
- conveys specific visceral sensation (smell) via olfactory nerve
- Does not relay in the thalamus.
- Connections with thalamus, hypothalamus, amygdaloid complex & hippocampal formation
What is the structure of the olfactory system?
- 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
Where is the Olfactory Nerve located?
- first CN
What is the Olfactory Bulb?
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
Structure of the Olfactory bulb
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.
Synaptic Organisation of olfactory bulb
Types of Synapses on olfactory bulb
- lateral inhibition
Olfactory tract
- 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
medial olfactory stria of olfactory tact
- turns medially behind the parolfactory area and ends in the subcallosal gyrus
lateral olfactory stria of olfactory tract
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
Describe the Olfactory Cortex
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
Secondary Olfactory Cortex
- entorhinal area of gyrus parahippocampalis (area28).
- Impulses from primary areas.
- efferents to hippocampus
Orbitofrontal cortex of olfactory cortex
- Impulses from nucl. medialis dorsalis thalami
- conscious preception of smell
Pathways in the olfactory system
What is the Limbic System
- 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
Limbic system term by Paul Maclean
- visceral brain
- triple concept of brain evolution
Hypothalamus
Nucleus accumbens
Nucleus amygdaloideus
orbitofrontal cortex
Parts & Connections of the limbic system
List of parts of the limbic system
What is the limbic lobe
- 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
External ring of limbic cortex
Internal ring of limbic cortex
- paraterminal gyrus (subcallosal)
- indusium griseum
- hippocampal formation
Hippocampal formation
- 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
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
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)
Efferent Connections of the Amygdala
Amygdala and Emotional Response
Amygdala and fear
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
Limbic circuit of Papez
neural circuit for the control of emotional expression
