Olfaction and the limbic system Flashcards
Recall the composition of the olfactory epithelium
Bipolar olfactory neurons
Sustentacular cells
Basal cells
Recall the structure of the olfactory system
Made up of an olfactory bulb and tract, bilaterally
What cells make up the olfactory bulb?
Mitral cells (second order neurons)
Where in the olfactory system is pathology seen in Parkinson’s disease?
Olfactory bulb
In which regions of the cerebrum does olfactory processing take place?
Piriform and orbitofrontal cortices
Why does smelling something tasty lead to salivation?
Olfactory connections to the brainstem cause autonomic responses
What is the clinical significance of the location of the brain regions involved in smell?
Piriform cortex is in temporal lobe
Temporal lobe often involved in epilepsy
Epileptics can often detect a prodromal aura
What is the term given to an absence of a sense of smell?
Anosmia
What does “limbus” mean and how does this describe the location of the limbic system?
Limbus = rim
= rim of cortex adjacent to corpus callosum and diancephalon
What is the general function of the limbic system?
Aimed at survival of individual
Recall 4 behaviours that are controlled by the limbic system
Homeostasis (nutrition)
Agonistic behaviour
Sexual behaviour
Memory
What are the key structures that make up the Papez circuit and where are they located?
Hippocampus
Amygdala
= temporal lobe
Recall the afferent and efferent pathways connected to the hippcampus
Afferent: Perforant pathway
Efferent: fornix
What is the alternative name for the fornix?
Fimbria
What are the functions of the hippocampus?
Short term memory and learning
Recall 2 pathologies of the hippocampus
Alzheimer’s (severely shrinks hippocampus)
Epilepsy
Describe the location and connections to the hippocampus of the amygdala
In white matter - has connecting fibres to hippocampus but no absolute connections
Where are the mamillary bodies located?
Other end of fornix to hippocampus
Recall the areas of the brain affected by Alzheimer’s as the disease progresses
Hippocampus –> parietal lobe –> frontal lobe
Describe the connection of the mamillary bodies to the thalamus
Connected to arcuate nucleus
Connected via mamillo-thalamic tract
Recall the main afferent anf efferent connections of the amygdala
Afferent: (BOTH SETS) 1. Olfactory cortex 2. Septum 3. Temporal neocortex 4. Hippocampus 5. Brainstem Efferent: Stria terminalis
What is the function of the amygdala?
Producing feelings of fear/ anxiety
What pathology is associated with loss of amygdala function?
Kluver-Bucy syndrome:
bilateral lesions of anterior temporal lobe including amygdaloid nucleus
Recall the symptoms of Kluver-Bucy syndrome
Hyperorality
Hypersexuality
Loss of fear
Visual agnosia
Where is the septum pellucidum located?
Between the 2 lateral ventricles in the brain
Recall the afferents and efferents of the septum pellucidum?
Afferent: amygdala olfactory tract hippocampus brainstem Efferent: Stria medularis thalami hippocampus hypothalamus
Where are the septal nuclei located?
Base of the septal membrane
What is the function of the septum?
Reinforcement and reward
Which pathway mediates drug dependence?
Mesolimbic pathway (Dopaminergic)
Where in the midbrain can dopaminergic neurons be found?
Ventral tegmental area
Where is the ventral tegmental area of the brainstem?
Just medial to the substantia nigra in the midbrain
Describe the projection of dopaminergic neurons that originate in the VTA
Project via medium-forebrain bundle to nucleus accumbens
What effect do drugs of abuse have on dopamine
Increase DA release in the nucleus accumbens
