Olfaction and the Limbic system

Question 1

how many different odours can we smell?

Answer 1

2000-4000

Question 2

what is contained in the olfactory epithelium [3]?

Answer 2

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

Question 3

through which bone does the olfactory bulb project its neurones

Answer 3

ethmoid bone

- it has fenestrations

Question 4

how does loss of olfactory epithelium change?

Answer 4

progressive with age

Question 5

olfactory pathway to promote autonomic responses

Answer 5

• 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.

Question 6

clinical deficit in smell

Answer 6

anosmia

Question 7

prodromal auras

Answer 7

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

Question 8

example of disease that targets the olfactory bulbs

Answer 8

Parkinsons

Question 9

what is the limbic system responsible for?

Answer 9

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

Question 10

what are the components of the limbic system?

what is the function of the limbic system?

Answer 10

olfactory bulbs 
hypothalamus
amygdala
hippocampus
thalamus
frontal lobe

function:

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

Question 11

emotional experience section of Papez Circuit

Answer 11

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

Question 12

what connects the hippocampus to the hypothalamus?

Answer 12

fornix

Question 13

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

Answer 13

mamillothalamic tract (MTT)

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

Question 14

what connects the cingulate cortex to the hippocampus?

Answer 14

cingulum bundle

runs along the midline of the corpus callosum

Question 15

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

Answer 15

emotional colouring using previous memory

Question 16

what is DTI used for?

Answer 16

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).

Question 17

what is the afferent pathway of hippocampus?

Answer 17

perforant pathway

coming from the enterohinal cortex

Question 18

what is the efferent pathway of hippocampus?

Answer 18

fimbria/ fornix
towards the mammilary bodies

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

Question 19

function of hippocampus

Answer 19

memory and learning

Question 20

what are 2 pathologies of the hippocampus?

Answer 20

1) Alzheimers
2) Epilepsy

remember hippocampus is in the medial temporal lobe

Question 21

What do Alzheimers patients present with?

Answer 21

cortical atrophy affecting the hippocampus particularly

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

Question 22

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

Answer 22

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

Question 23

what causes the formation of senile plaques in Alzheimers?

Answer 23

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.

Question 24

what is affected in early stage Alzheimers?

Answer 24

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

then parietal
then frontal

Question 25

what is affected moderate stage Alzheimers?

Answer 25

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

Question 26

what is affected in late stage Alzheimers?

Answer 26

 Affected – Frontal lobe. |  Symptoms – Loss of executive skills (e.g. recognition).

Question 27

what are the afferent connections of amygdala?

Answer 27

``` Olfactory cortex septum temporal neocortex hippocampus brainstem. ``` efferent is stria terminalis

Question 28

what is the efferent connection of amygdala?

Answer 28

Stria terminalis.

Question 29

functions of amygdala

Answer 29

o Fear and anxiety (and opposite). o Fight or flight. bilateral lesion--> Kluver Bucy Syndrome

Question 30

pathology of amygdala

Answer 30

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.

Question 31

what structured are associated with aggression?

Answer 31

hypothalamus brainstem (periaqueductal grey) amygdala

Question 32

what chemical stimulates aggression? | from where?

Answer 32

5-HT (serotonin) from the raphe nuclei (brainstem) other structures involved in aggression are: - hypothalamus - periaqueductal grey

Question 33

afferent connection of septum

Answer 33

Amygdala, olfactory tract, hippocampus, brainstem.

Question 34

efferent connection of septum

Answer 34

Stria medularis thalami, hippocampus, hypothalamus.

Question 35

function of the septum

Answer 35

reinforcement and reward (nucleus accumbens)

Question 36

pathways in the median forebrain bundle

Answer 36

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

Question 37

transmitter used in mesolimbic pathway

Answer 37

dopamine

Question 38

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

Answer 38

Ventral Tegmental Nucleus via mesolimbic fibres of the medial forebrain bundle

Question 39

which drugs increase dopamine in the nucleus accumbens

Answer 39

``` o Opioids. o Nicotine. o Amphetamines. o Ethanol. o Cocaine. ```

Question 40

how is the increase in dopamine achieved in the Nucleus accumbens

Answer 40

- stimulating the midbrain neurones to release more DA | - inhibiting its reuptake

Question 41

which drug inhibits the reuptake of dopamine

Answer 41

cocaine | opioids

Question 42

which lobe is epilepsy focused on?

Answer 42

temporal

Question 43

how does epilepsy affect smell sensation? | what does it give rise to?

Answer 43

- 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

Question 44

what are the causes of anosmia?

Answer 44

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