Limbic system Flashcards
What is the role of the Olfactory system?
Responsible for sense of smell.
What are the components of the olfactory epothelium?
Bipolar olfactory neurones
Sustentacular cells
Basal cells
What is the role of the basal cells?
allow for regeneration.
What is the role of the sustentacular cells?
provide metabolic support.
Explain the structure of the bipolar olfactory neurones.
2 processes.
External sensory receptor component, and one to the olfactory bulb.
Where is the olfactory bulb located?
Sits above the cruciform plate.
What is the role of the olfactory bulb?
Receive axons from olfactory epithelial bipolar cells. These synapse at a glomerulus with a second order olfactory neurone
What is the role of the olfactory tract? What does it divide into?
Carry second order neurones (olfactory mitral cells).
Splits into medial and lateral olfactory stria.
What can damage to the cortices lead to?
Inhibition of normal smell processes
Where does higher processing of olfactory sensory input occur?
piriform and orbitofrontal cortices
Label diagram showing location of olfactory epithelium + its components
Explain the prodromal aura epileptic patients might experience.
Epilepsy often focused in temporal lobe (containing piriform complex). Seizure can be anticipated when smelling something not present.
What is anosmia? How can it arise?
Clinical deficity of olfactory system.
mid-face trauma –> fracturing of cribiform plate + shearing of neurones.
What disease is a loss of smell a predictor for?
Parkinson’s
List some roles of the limbic system.
Memory
Sexual/reproductive behaviour
Defence/attack behaviour
Maintenance of homeostasis by activating visceral effectors, modulating pit hormone release and initiating feeding/drinking
What brain structures are involved in the limbic system?
Amygdala anteriorly, hippocampus posteriorly (on floor of inferior horn of lateral ventricle), cingulate cortex, olfactory tracts (?)
What happens to the hippocampus in Alzheimer’s?
Shrinkage.
What is the primary afferent pathway of the hippocampus?
perforant pathway from the entorhinal cortex. All other cortical regions go via entorhinal cortex.
What are the destinations of efferent hippocampal information?
fimbria/fornix (Papez circuit)
Where is the fornix located?
Immediately below the corpus callosum.
Where are mammillary bodies found?
At the ends of the fornix.
What is the main output of the hippocampus?
fornix
Broadly outline pathology of Alzheimer’s
cortical atrophy. Loss of neurones + ventricles grossly enlarged. Hippocampal shrinkage + sulci widening.
Compare the intracellular and extracellular patholgoy of Alzheimer’s
Intracellular - cytoskeleton compromised. Tau protein build up.
Extracellular - senile plaques of protein develop between cells in neurophil.
Broadly outline the clinical progression of Alzheimer’s and the associated anatomical changers.
Early - short term memory issues. Hippocampus and enteroginal cortex.
Moderate - depressing apraxia. Parietaql lobe.
Late - executive skill loss. Frontal lobe.
What is the Papezs circuit?
a neural circuit to control emotional expression.
What are the components of the Papez ciruit and their roles?
Hippocampus: present on the floor of the inferior horn of the lateral ventricle, outputting to the fornix
Fornix: fibre pathway from the inferior horn, passing under the corpus callosum to synapse in the mamillary bodies (hypothalamus)
Mammillo-thalamic tract: projects to the anterior nucleus of the thalamus
ANT: produces thalamo-cortical projections to the cingulate cortex
Cingulate cortex: allows for emotional colouring from the neocortex
What connects the cingulate cortex to the hypothalamus?
Cingulum bundle.
What is the role of the amygdala?
Perception of fear, anxiety and fight/flight
What structures provide afferent information to the amgydala?
olfactory cortex, septum, temporal neocortex, hippocampus and brainstem
Where does the amgydala output to?
stria terminalis.
Explain Kluver-Bucy syndrome.
bilateral lesions of anterior temporal lobe –> hyperorality (exploring with mouth), loss of fear, visual agnosia (can’t recognise objects) and hypersexuality
What are the main functions of the septum?
reinforcement and reward.
What structures provide afferent information to the septum?
amygdala, olfactory tract, hippocampus and brainstem
Where does the septum output to?
stria medularis thalami, hippocampus, hypothalamus
What areas are associated with aggression?
hypothalamus, brainstem (periaqueductal grey area) and amygdala
Explain the route of the mesolimbic pathway.
Ventral tegmental area of midbrain origin –> cortex, amgydala and nucleus accumbens via medial forebrain.
What NT does the mesolimbic pathway use?
Dopameme
How do opioids and amphetamines increase DA release in the nucleus accumbens?
Stimulating midbrain neurones
Promoting DA release
Inhibiting DA reuptake
