Olfaction and the Limbic System Flashcards
What the three types of cell that makes up the olfactory epithelium?
Bipolar Olfactory Neurones (primary olfactory neurones) Sustentacular Cells – support cells mainly providing metabolic support for bipolar olfactory neurones Basal Cells – there is some regeneration in olfactory neurones
Where is the olfactory bulb found?
Sitting on top of the cribriform plate of the ethmoid bone.
Which cells synapse within the olfactory bulb?
The bipolar cells pass their axons through the cribriform plate to synapse with the second order neurones (olfactory bulb mitral cells) in the glomerulus within the olfactory bulb
What structure do the second order neurones form and what does this structure split into?
Olfactory tract It splits to form the medial and lateral olfactory stria
Where does higher processing of smell take place?
Piriform Cortex Orbitofrontal Cortex
What is a clinical deficit in the olfactory system called?
Anosmia
What is a common cause of anosmia?
Mid-face trauma Impact with enough force could cause a fracture of the cribriform plate, shearing the neurones going from the olfactory epithelium to the olfactory bulb
Explain the significance of the piriform cortex’s location with regards to epileptic patients.
The piriform cortex is found within the medial temporal lobe. Epilepsy is often focused in the temporal lobe. If the epileptic focus is close to the piriform cortex then these people with epilepsy will experience PRODROMAL AURA (they are made aware of an imminent seizure because they’ll smell something that’s not there)
Neurodegenerative disease is a relatively common cause of anosmia. State two neurodegenerative diseases that could cause anosmia.
Alzheimer’s disease Parkinson’s disease
What is the limbic system?
A rim of cortex adjacent to the corpus callosum and diencephalon
What are the roles of the limbic system?
Homeostasis (mainly hypothalamic functions such as regulation of food intake and pituitary hormone release) Agonistic behaviour (fight or flight) Sexual and reproductive behaviour Memory
State two important parts of the limbic system that are found within the temporal lobes.
Hippocampus and Amygdala
What circuit are these structures a part of?
Papez Circuit
What is the cortical representation of the limbic system?
Cingulate Cortex
What is the function of the Papez circuit?
It is a neural circuit for the control of emotional expression
Describe/draw the papez circuit.
What conditions could damage the mammillary bodies leading to amnestic issues?
Chronic Alcoholism Wernicke-Korsakoff Syndrome
What is our emotional expression ‘coloured’ by?
Neocortex - by previous experience
What form of imaging is used to study the limbic system?
Digital Tensor Imaging – shows co-instant activity in different parts of the brain thus showing which parts of the brain are working together
Describe the afferent pathway of the hippocampus.
Afferent Pathway = Perforant Pathway The entorhinal cortex is linked to the hippocampus via the afferent pathway (perforant pathway) The entorhinal cortex receives input from all other parts of the neocortex
What is the efferent pathway of the hippocampus called?
Fimbria/Fornix
What are the functions of the hippocampus?
Memory and Learning
What happens to the hippocampus in Alzheimer’s disease?
It shrinks severely
Describe the spatial relations of the hippocampus and the fornix to other important brain structures.
The hippocampus is found on the floor of the inferior horn of the lateral ventricles The fornix comes out of the hippocampus and passes under the corpus callosum It then dives inferior and anteriorly towards the mammillary bodies
Describe the appearance of advanced Alzheimer’s disease on a CT head scan in the coronal plane.
There will be extensive cortical atrophy - Temporal and frontal lobes massive atrophy, parietal and occipital relatively unaffected. Atrophy of hippocampus The ventricles would appear enlarged There will also be widening of sulci
State two microscopic hallmarks of neurodegeneration.
Tau Immunostaining Intracellular pathology – the cytoskeleton has been broken down. Tau protein hyper-phosphylated begins to clump intracellulaly Senile Plaques Extracellular pathology Lumps of protein sitting in between cells in the neuropil
Describe the anatomical progression of Alzheimer’s disease, including the symptoms experienced.
Early Hippocampus and entorhinal cortex affects Short-term memory problems Moderate Parietal lobe (where you have your procedural memory) Example of effects: dressing apraxia Late Frontal lobe Loss of executive skills (loss of ability to recognise and interact with loved ones)
Where is the amydala found?
In the white matter of anterior temporal lobe
What are the afferent connections of the amygdala?
Olfactory Cortex Septum (septal nuclei) Temporal Neocortex Hippocampus Brainstem
What is the main output pathway of the amygdala?
Stria terminalis to the hypothalamus
What is the function of the amygdala?
Fear and Anxiety (fight or flight)
In Alzheimer’s and Parkinson’s disease, the amygdala starts showing pathology early on. What are the possible outcomes of this?
Patients could either become terrified of everything or they could become totally disinhibited and become quite aggressive
State and describe a syndrome affecting the amygdala.
Kluver-Bucy Syndrome Bilateral lesions of the anterior temporal lobe (including amygdaloid nucleus) Symptoms Hyperorality Hypersexuality Loss of Fear aggression Visual Agnosia
State three structures associated with aggression.
Hypothalamus Brainstem (periaqueductal grey matter) Amygdala
What are the main afferent connections of the septum?
Amygdala Olfactory Tract Hippocampus Brainstem
What are the functions of the septum?
Reinforcement and Reward
Name another structure that is important in the reward system.
Nucleus Accumbens
Describe another dopaminergic pathway other than the nigro-striatal pathway that is affected in Parkinson’s disease.
Meso limbic pathway Ventral Tegmental Area (VTA) of the midbrain –> Median Forebrain Bundles –> Cortex + Nucleus Accumbens + Amygdala
Name a structure that is important in drug dependence.
Nucleus Accumbens
What effect do all drugs of abuse have on the nucleus accumbens?
They all increase dopamine release in the nucleus accumbens
What are the components of the limbic system?
olfactory bulbs, hippocampus, hypothalamus, amygdala, anterior thalamic nuclei fornix & columns of fornix mammillary body, septum pellucidum, habenular commissure, cingulate gyrus, parahippocampal gyrus, entorhinal cortex,
What controls anger and agression?
Amygdala communicating with the hypothalamus with prefrontal cortex input
where are memories initailly processed then stored?
Hippocamput - initial processing Parietal lobe - storage
