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LCRS Neuro > Olfaction and the Limbic system > Flashcards

Olfaction and the Limbic system Flashcards

1
Q

how many different odours can we smell?

A

2000-4000

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2
Q

what is contained in the olfactory epithelium [3]?

A

o Bipolar olfactory neurones (primary neurone)
o Sustentacular cells – metabolic/support cells.
o Basal cells – regenerative stem cells.

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3
Q

through which bone does the olfactory bulb project its neurones

A

ethmoid bone

- it has fenestrations

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4
Q

how does loss of olfactory epithelium change?

A

progressive with age

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5
Q

olfactory pathway to promote autonomic responses

A
  • bipolar olfactory neurones (primary neurone)
  • via cribriform plate
  • olfactory bulb has mitral cells (secondary neurone)
  • olfactory tract
  • olfactory stria (medial and lateral)
  • Piriform cortex (lateral stria), Orbitofrontal cortex (medial stria)

connections then promote autonomic responses.

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6
Q

clinical deficit in smell

A

anosmia

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7
Q

prodromal auras

A

In some epilepsy patients, prior to seizures they begin to smell something that isn’t there , indicative on pending seizure

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8
Q

example of disease that targets the olfactory bulbs

A

Parkinsons

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9
Q

what is the limbic system responsible for?

A

survival instinct: the 4 Fs

o Fighting (fight or flight) 
- Agonistic behaviour – defence and attack, aggression or fear 
o Fucking 
- Sexual behaviour.
o Forgetting
- Memory
o Feeding
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10
Q

what are the components of the limbic system?

what is the function of the limbic system?

A 
olfactory bulbs 
hypothalamus
amygdala
hippocampus
thalamus
frontal lobe

function:

  • feeding
  • fucking (sexual behaviour and reproduction)
  • fighting (flight or flight, fear and aggression)
  • forgetting (memory)
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11
Q

emotional experience section of Papez Circuit

A
  • Hippocampus to..
  • hypothalamus (mam. bodies) to…
  • Anterior nucleus of Thalamus too…
  • Cingulate cortex back to the hippocampus
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12
Q

what connects the hippocampus to the hypothalamus?

A

fornix

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13
Q

what connects the mamillary bodies of the hypothalamus to the anterior nucleus of the thalamus?

A

mamillothalamic tract (MTT)

projects from mamillary bodies of the hypothalamus to the anterior nucleus of the thalamus

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14
Q

what connects the cingulate cortex to the hippocampus?

A

cingulum bundle

runs along the midline of the corpus callosum

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15
Q

what does the neocortex contribute to in the Papez Circuit (control of emotional expression)?

A

emotional colouring using previous memory

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16
Q

what is DTI used for?

A

Diffusion Tensor Imaging used for visualising the limbic system:

theorise the pathways/networks in the brain to highlight parts of the brain that are interconnected when performing certain actions/functions (e.g. crying).

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17
Q

what is the afferent pathway of hippocampus?

A

perforant pathway

coming from the enterohinal cortex

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18
Q

what is the efferent pathway of hippocampus?

A

fimbria/ fornix
towards the mammilary bodies

fimbria (path attached to hippocampus)
fornix (detached, when it leaves)

19
Q

function of hippocampus

A

memory and learning

20
Q

what are 2 pathologies of the hippocampus?

A

1) Alzheimers
2) Epilepsy

remember hippocampus is in the medial temporal lobe

21
Q

What do Alzheimers patients present with?

A

cortical atrophy affecting the hippocampus particularly

  • loss of neurones
  • ventricular enlargement
  • widening sulci
  • frontotemporal lobe more atrophied than occipital (unique to Alzheimers)
22
Q

what can be seen in tau immunostaining of the brain in Alzheimers?

A

in Alzheimer’s disease, sporadic tau proteins in the brain become hyper-phosphorylated and this stops them functioning so they die.

23
Q

what causes the formation of senile plaques in Alzheimers?

A

alpha-beta proteins build up in the brain in Alzheimer’s and when there is too much, the cells excrete it and the proteins form toxic plaques.

24
Q

what is affected in early stage Alzheimers?

A

 Affected – hippocampus & entorhinal cortex.
 Symptoms – short-term memory loss.

then parietal
then frontal

25
Q

what is affected moderate stage Alzheimers?

A

Affected – Parietal lobe.
Symptoms
– Dressing apraxia (inability to perform purposive actions) loss of procedural memory

26
Q

what is affected in late stage Alzheimers?

A

 Affected – Frontal lobe.

 Symptoms – Loss of executive skills (e.g. recognition).

27
Q

what are the afferent connections of amygdala?

A 
Olfactory cortex
septum
temporal neocortex
hippocampus
brainstem.

efferent is stria terminalis

28
Q

what is the efferent connection of amygdala?

A

Stria terminalis.

29
Q

functions of amygdala

A

o Fear and anxiety (and opposite).
o Fight or flight.

bilateral lesion–> Kluver Bucy Syndrome

30
Q

pathology of amygdala

A

o Kluver-Bucy Syndrome – post-trauma, medial temporal lobes are sheared off middle cranial fossa and amygdala damaged.

o Symptoms – hyperorality (explore things by mouth) , loss of fear, visual agnosia, hypersexuality.

31
Q

what structured are associated with aggression?

A

hypothalamus
brainstem (periaqueductal grey)
amygdala

32
Q

what chemical stimulates aggression?

from where?

A

5-HT (serotonin)
from the raphe nuclei (brainstem)

other structures involved in aggression are:

  • hypothalamus
  • periaqueductal grey
33
Q

afferent connection of septum

A

Amygdala, olfactory tract, hippocampus, brainstem.

34
Q

efferent connection of septum

A

Stria medularis thalami, hippocampus, hypothalamus.

35
Q

function of the septum

A

reinforcement and reward (nucleus accumbens)

36
Q

pathways in the median forebrain bundle

A

midbrain (VTN) to the cortex, nucleus accumbens and amygdala via the median forebrain bundle using mesocortical and mesolimbic fibres

37
Q

transmitter used in mesolimbic pathway

A

dopamine

38
Q

where do neurones to the nucleus accumbens project from in the midbrain

A

Ventral Tegmental Nucleus

via mesolimbic fibres of the medial forebrain bundle

39
Q

which drugs increase dopamine in the nucleus accumbens

A 
o	Opioids.
o	Nicotine.
o	Amphetamines.
o	Ethanol.
o	Cocaine.
40
Q

how is the increase in dopamine achieved in the Nucleus accumbens

A
  • stimulating the midbrain neurones to release more DA

- inhibiting its reuptake

41
Q

which drug inhibits the reuptake of dopamine

A

cocaine

opioids

42
Q

which lobe is epilepsy focused on?

A

temporal

43
Q

how does epilepsy affect smell sensation?

what does it give rise to?

A
  • piriform cortex (lateral stria) and orbitofrontal cortex (medial stria) are located in the temporal lobe
  • gives rise prodromal auras:
    due to an overactive piriformis cortex leading to a sensation of smell before seizures
44
Q

what are the causes of anosmia?

A

1) mid-face trauma–> fracture to cribriform plate, shearing off the bipolar olfactory neurones
2) neurodegenerative disease e.g. Parkinson’s

LCRS Neuro (19 decks)

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