Limbic System Flashcards
Describe the olfactory system
2000-4000 different odours
Molecular mechanism largely unknown
progressive loss with age
What is in the olfactory epithelium
bipolar olfactory neurons sustentacular cells (support) basal cells (turnover of neurones)
Describe the structure of the olfactory system
Olfactory receptor cells -> glomerulus -> second-order olfactory neurone -> olfactory tract
Cribiform plate and olfactory bulb
What structures are involved in the olfactory system
Olfactory bulb (mitral cells) Olfactory tract Olfactory stria Piriform and orbitofrontal cortex Connections to brainstem (promotes autonomic responses)
What is a clinical deficit in the olfactory system known as
Anosmia
Prodromal auras
Describe the olfactory system in the brain
Olfactory bulb Olfactory tract Piriform cortex Orbitofrontal cortex Lateral olfactory stria Medial olfactory stria
What is the limbic system
Rim or limbus of cortex adjacent to corpus callosum and diencephalon
Structurally and functionally interrelated areas considered as a single functional complex
What are the functions of the limbic system
maintenance of homeostasis
agonistic (defence & attack) behaviour
sexual & reproductive behaviour
memory
How does the limbic system maintain homeostasis
Activation of visceral effector mechanisms
Modulation of pituitary hormone release
Initiation of feeding and drinking
What structures are involved in limbic system
Frontal lobe Thalamus Hypothalamus Hippocampus Amygdala Olfactory bulb
Describe the Paper circuit
Neocortex to cingulate cortex 1. Cingulate cortex Cingulum bundle 2. Hippocampus Fornix 3. Hypothalamus (maxillary bodies) Mammillothalamic tract 4. Anterior nuclear of thalamus
What is involved in emotional colouring, experience and expression
Colouring - neocortex
Experience - cingulate
expression - Hypothalamus
What are the functions of the hippocampus and what can it be involved in clinically
Memory and learning
Alzheimer’s disease
Epilepsy
What are the main connections of the hippocampus
Afferent: Perforant pathway
Efferent: Fimbria/ fornix
Where is the hippocampus
Below the medial temporal lobe
Medial to the inferior horn of the lateral ventricle
Which structures can be found in the hippocampal circuitry
Hippocampus -> fornix -> mammillary bodies Seahorse shape (two Cs)
What happens in Alzheimers
Cortical atrophy
Ventricle enlargement
Plaques
Tangles
Describe the anatomical progression of Alzheimers
Early
Hippocampus and entorhinal cortex
Short-term memory problems
Moderate
Parietal lobe
Dressing apraxia
Late
Frontal lobe
Loss of executive skills
What are the main connections of the amygdala
Afferent: Olfactory cortex, septum, temporal neocortex, hippocampus, brainstem
Efferent: Stria terminalis
What are the functions of the amygdala and what can it be involved in clinically
Fear and anxiety
Fight of flight
Kluver-Bucy syndrome
Where is the amygdala
Anterior to the hippocampus
Grey matter nucleus embedded in the white matter of the temporal lobe
Describe Kluver-bucy syndrome
Hyperorality
Loss of fear
Visual agnosia
Hypersexuality
Which structures are associated with aggression
Hypothalamus
Brainstem (periaqueductal grey)
Amygdala
5-HT (serotonin) in raphe nuclei
What are the main connections of the septal nuclei
Afferent: Amygdala, olfactory tract, hippocampus, brainstem
Efferent: Stria medularis thalami, hippocampus, hypothalamus
What is the function of the septal nuclei
Reinforcement and reward
Describe the drug dependence mechanism
Opioids, nicotine, amphetamines, ethanol and cocaine all increase dopamine (DA) release in nucleus accumbens
Stimulate midbrain neurons, promote DA release or inhibit DA reuptake
Other neurotransmitters also modify this system
Describe the mesolimbic pathway
Midbrain -> MFB -> cortex, nucleus accumbens, amygdala
