Flashcards in Olfactory and limbic system Deck (42):
What are the support cells of the olfactory system?
Sustentacular cells providing metabolic support
What is the purpose of basal cells in the olfactory system?
They are needed for regeneration of olfactory neurones.
Describe the organisation of the olfactory system
Bipolar olfactory neurones lie in the olfactory epithelium
The axons project into the cruciform plate of the ethmoid bone and synapse at the glomerulus
They synapse with olfactory mitral cells which then travel via the optic tract to the brain (split into medial and lateral olfactory stria)
Which parts of the brain are involved in smell?
Piriform and Orbitofrontal cortices
What is anosmia and possible cause?
Loss of sense of smell
Mid face trauma; it can break the cribriform plate and shear off neurones travelling from the olfactory epithelium
Neurodegenerative disease; can be a presenting symptom of PD and Alzhemier's.
How is epilepsy and the olfactory system related?
Epilepsy seizures are mostly localised in the temporal lobe where the piriform cortex is located.
Those with epilepsy may experience Prodromal aura, lose sense of smell before a seizure.
What are some of the purposes of the limbic system?
Activation of visceral effector mechanisms
Initiation of feeding and drinking
Modulation of pituitary hormones
Where does the medial stria of the ophthalmic tract travel to?
Travels to the nasal septum -> second order processing in the orbitofrontal cortex
Where does the lateral stria of the ophthalmic tract travel to?
Projects to the piriform cortex in the medial temporal lobe
What are the structures of the limbic system?
What is the cortical representation of the limbic system?
The cingulate cortex, just above the corpus callosum.
Where is the papez circuit located?
Located next to the corpus callosum and diencephalon.
All structurally connected to function as a single complex.
Where is the amygdala located?
In the white matter of the anterior part of the temporal lobe
Where is the hippocampus located?
In the inferior horn of the floor of the lateral ventricles.
What is the purpose of the papez circuit?
It is neural circuit important for control in emotional expression.
Outline the basic principles of the papez circuit
Hippocampus -> via Fornix to Mamillary bodies -> via mammal-thalamic tract to anterior horn of the thalamus -> via thalami-cortical projections to cingulate cortex (+ neocortex contributions)
What is the function of the hypothalamus?
Initiates autonomic response
What is the function of the cingulate cortex?
What is the function of the neocortex?
Modifies behaviour based on previous experience
Frontal and parietal lobes contribute to this
What is diffusion tensor imaging used for?
Shows co-incidental activity in different parts of the brain
Able to suggest areas for functional structures
Describe the afferent pathway of the hippocampus
Perforate pathway, it receives input from the entorhinal cortex which receives input from every other neocortical area
Describe the efferent pathway of the hippocampus
Output pathway from the hippocampus, part of the papez circuit
What is the significance of the hippocampus in AD?
In AD, there is significant shrinkage of the hippocampus. This will affect a person's memory and learning.
What type of cortical atrophy is likely to be seen in an patient with AD?
Thinning gyro, Widening sulci
Frontotemporal damage is more extensive than occipital
What is an example of intracellular pathology of AD?
In tau protein immunostaining; cytoskeleton is compromised.
Becomes hyperphosphorylated and stops functioning.
What is an example of extracellular pathology of AD?
Beta protein is found in lumps in the brain
Excess is sent into the parenchyma by the cells
What is the presentation of early AD?
Affects hippocampus and entorhinal cortex
Short term memory loss
Able to perform rote tasks
What is the presentation of moderate AD?
Affects the parietal lobe (procedural tasks)
What is the presentation of late AD?
Affects the frontal lobe
Loss of executive skills
List the afferent connections to the amygdala
What is the efferent connection to the amygdala
Stria terminalis (to hypothalamus)
What structure is damaged in the limbic system in chornic alcoholism?
The mamillary bodies, also damaged in Wernicke-korsakoff syndrome
What is the function of the amygdala?
Fear and anxiety
What is Kluver-bucy syndrome?
Caused by bilateral lesions to the anterior temporal lobe
Results in; hyperorality, loss of fear, hypersexuality, visual agnosia
What are the structures possibly involved in aggression?
Brainstem (periaqueductal grey matter)
Which neurotransmitter is involved in aggression?
Serotonin (5-HT) in raphe nuclei of the brainstem
What are the main afferent connections to the septum?
What are the main efferent connections to the septum?
Stria medularis thalami
What is the function of the septum?
Reward and reinforcement centre
What is the mesolimbic pathway?
It is a secondary dopamine pathway.
From the ventral segmental area of the midbrain -> projections go to the medial forebrain bundle -> nucleus accumbens (increase dopamine release), amygdala, frontal cortex
What is the difference in the substantial nigra and ventral tegmental nucleus dopamine production?
Substantial nigra dopamine projects to the basal ganglia.
Ventral tegmental nucleus projects to the nucleus accumbens.