Olfactory and limbic system Flashcards
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 Agnostic behaviour Sexual behaviour Memory
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?
Frontal lobe Olfactory bulbs Thalamus Hypothalamus Amygdala Hippocampus
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?
Emotional expression
Initiates autonomic response
What is the function of the cingulate cortex?
Emotional experience
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
Fimbria/Fornix
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
Shrunken hippocampus
Larger ventricles
Frontotemporal damage is more extensive than occipital
