Olfaction and the limbic system Flashcards
What 3 types of cells can you get in the olfactory epithelium in the upper part of the nose?
- Primary, bipolar olfactory neurones
- Sustentacular cells - support these primary bipolar olfactory neurones
- Basal cells - in the nasal mucosa, to produce new olfactory cells (limited regeneration)
3 reasons for loss of smell or even anosmia (loss of smell)
- Progressive loss with age
- Neurodegenerative disorders e.g. Parkinson’s, Alzheimers
- Trauma - to the ethmoid bone which shears off the primary olfactory neurones
Describe the anatomical path along which the smell impulses travel
- From the primary bipolar neurones in the upper part of the nose
- Travels up and pierces the cribriform plate (part of the ethmoid bone) into the brain
- Here it synapses with the mitral neurones (second order neurones) of the olfactory bulb in a glomerular-like arrangement
- The mitral neurones then travel along olfactory tracts which lies along the underside of the frontal lobe
- The olfactory tracts then split into medial and lateral striae
- These travel to the olfactory processing centres in the orbitofrontal cortex and the piriform cortex of the temporal lobe
How does smell evoke autonomic response?
Neurones in the olfactory processing centres of the orbitofrontal and piriform cortices project down the brainstem and exert autonomic influences e.g. you start salivating when you smell some aromatic food
What does it mean to say that in epilepsy you can have prodromal aura, and how?
- Temporal lobe epilepsy → affects piriform cortex → evokes an artificial sense of smell → you smell some random smell just before you have a seizure
What are the 2 pathways along which pathology can access the brain?
- Up the nose
- Retrograde transport originating from the gut along the vagus nerve
1) What is the protein aggregate associated with Parkinson’s?
2) What other pathological sign can be seen under a microscope?
1)
- Alpha-synuclein
2)
- Lewy-Bodies
Where is some of the earliest pathology of Parkinson’s disease located?
- In the motor nucleus of the vagus
Define the limbic system
- Rim or limbus of cortex, adjacent to the corpus callosum and diencephalon
- Series of structurally and functionally interrelated areas considered a functional unit
Give 4 functions of the limbic system
- Homeostasis maintenance (hypothalamic function) - modulation of pituitary hormone release and initiation of feeding and drinking
- Agonistic behaviour (fight or flight)
- Sexual and reproductive behaviour
- Memory - emotional response to environmental stimuli
Describe the Papez circuit for emotional response
- Cingulate cortex sends impulses via the cingulum bundle to the hippocampus
- The hippocampus stores the emotional stimulus and somewhat the evoked response and sends on the impulse via the fornix to the hypothalamus
- The hypothalamus is what causes the autonomic and otherwise emotional expression in response to the emotional stimulus and sends on the impulse via the MTT (mammilo-thalamic-tract) to the anterior nucleus of the thalamus
- The anterior nucleus of the thalamus sends the impulses back to the cingulate cortex
- The neocortex also exerts influence on this circuit to exert some ‘personality’ based modulation of the emotional response
Label this diagram of the Papez ciruit for emotional response to emotional stimuli
What is the afferent pathway for the hippocampus?
- The perforant pathway from the entorhinal cortex which receives input from lots of other cortical areas
What is the efferent pathway of the hippocampus?
- Out via fimbria / fornix (note they’re kinda the same its just fimbria is when its joint up at the start and fornix when it separates as it moves away)
What are the functions of the hippocampus?
- Short-term memory
- Learning
Identify the hippocampus bilaterally on this scan
Label this diagram of the hippocampus and associated circuitry
Label this diagram with the cortex removed and the corpus callosum excised with the back of the brain at the top of the page to reveal underlying structures (brains upside down)
Label this diagram of the hippocampus, with the irrelevant bits crossed out (ignore these ones)
What is this scan showing?- normal on the left and the one in question on the right
- Cortical atrophy in Alzheimer’s
1) In Alzheimer’s, what is the main finding that can be seen that is pathological upon microscopic observation and how do we see it? What is happening that causes these / how do they cause disease?
2) What is another microsopic pathological observation? What is it that causes these / how do they cause disease?
1)
- Tau immunostaining
- Shows the abnormal cytoskeletal proteins that cause cytoskeletal break down which leads to impairment of neuronal cell function so impairing memory formation
2)
- Senile plaques
- Protein laid down in hippocampus, affecting memory formation
