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Neuro > Neuro 14: Olfaction and limbic system > Flashcards

Neuro 14: Olfaction and limbic system Flashcards

1
Q

Cells in the olfactory epithelium

A

bipolar olfactory neurons (primary olfactory neurone)

sustentacular cells (support cells)

basal cells (potential for regeneration… unique)

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2
Q

Effect of age on smell

A

progressive loss with age

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3
Q

What cells pass throught the cribriform plate. What neurons do these synapse onto

A

olfactory receptor cells (bipolar)….

these then synapse onto the second order olfactory neurons (=mitral cells) in the olfactory bulb)

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4
Q

Pathway for olfactory system

A

Olfactory bulb (mitral cells)
Olfactory tract
Olfactory stria
Piriform and orbitofrontal cortex

Connections to brainstem promote autonomic responses (i.e. smell something you want to eat –> salivation)

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5
Q

What is clinical deficit of smell

A

Anosmia

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6
Q

Where is the piriform cortex

A

Temporal lobe (inferomedially)

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7
Q

What is a prodromal aura

A

If they have an epilepsy and the focus is near the piriform cortex, they can smell an odour that isn’t there, just before a seizure

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8
Q

Nose in parkinson’s

A

smell lost early…. easiest route of disease causing agents into the brain

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9
Q

Function of limbic system

A

Aimed at survival:
maintenance of homeostasis

agonistic (defence & attack) behaviour

sexual & reproductive behaviour

memory

or

HOMES (homeostasis, olfaction, memory, emotion, sexual and reproductive behaviour)

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10
Q

How does limbic system help to achieve homeostasis

A

via activation of visceral effector mechanisms, modulation of pituitary hormone release and initiation of feeding and drinking

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11
Q

Components of limbic system

A

Frontal lobe, thalamus, hippocampus, amygdala, hypothalamus, olfactor bulb and cingulate nucleus

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12
Q

What is the Papaz ciruit

A

Neocortex –> cingulate cortex

Cingulate cortex –> hippocampus (via cingulum bundle)

Hippocampus –> hypothalamus (via fornix)

Hypothalamus (mamillary bodis) –> anterior nuleus of thalamus (via mamillo-thalamic tract)

Thalamus –> cingulate cortex

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13
Q

Which structure achieves the following:

  • emotional colouring
  • emotional experience
  • emotional expression (response)
A

neocortex,
cingulate cortex
hypothalamus

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14
Q

Connections of hippocampus

A

Afferent: Perforant pathway
Efferent: Fimbria (=fornix)

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15
Q

Function of hippocampus

A

memory and learning

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16
Q

Clinical conditins involving problems with hippocampus

A

Alzheimer’s (short term memory loss), epilepsy

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17
Q

Where do the hippocampi sit

A

Lying in the floor of the inferior horn of the lateral ventricle

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18
Q

Where does the fornix project

A

From hippocampus, up and underneath corpus callosum, forward to the mamillary bodies

19
Q

Where does the amygdala sit

A

In the WHITE MATTER of the temporal lobe, medial to the hipoocampi ,which are in the floor of the latera lventircle

20
Q

Where does the perforant pathway come from

A

entorhinal cortex

21
Q

Signs of alzheimer’s

A 
enlgarment of the ventricles, 
cortical atrophy (in particular the temporal lobe and the parietal lobe...but strangely NOT in the motor or somatosensory cortex... weirdly? occipital lobe also not affected)

so motor, sensory and vision mostly left unaffected

22
Q

What are tangles in Alzheimers and what are plaques… which is thought to be cause

A

Through its isoforms and phosphorylation tau protein interacts with tubulin to stabilize microtubule assembly. All of the six tau isoforms are present in an often hyperphosphorylated state in paired helical filaments from AD. and you get cytoskeleton effects leading to tangles in neuorons (some neurons susceptible, some are not)….

then the dead material from within this cell can be dumped outside the cell leading to plaques

23
Q

Outline the anatomical progression of Alzheimer’s

A

Early
Hippocampus and entorhinal cortex
Short-term memory problems

Moderate
Parietal lobe
Dressing apraxia

Late
Frontal lobe
Loss of executive skills

24
Q

Connections of the amygdala

A

Afferent: Olfactory cortex, septum, temporal neocortex, hippocampus, brainstem

Efferent: Stria terminalis (going to hypothalamus, thalamus and septal nuclei)

25
Q

Function of amygdala

A

Fear & anxiety

Fight or flight

26
Q

In which clinical situituation is amygdala implicated

A

Kluver-Bucy syndrome

27
Q

Symptomy of kluver bucy

A

Hyperorality
Loss of fear
Visual agnosia
Hypersexuality

Sex
Mouth
Agnosia
Loss of fear

(due to bilateal temporal lobe contusion)

28
Q

Strcutures related to aggression

A

Hypothalamus

Brainstem (periaqueductal grey)…. seratonin in raphe nuclei involved (as well as other nuclei)

Amygdala

29
Q

What is the septal nuclei

A

Nuclei at the base of the septum between the anterior lateral ventricles

30
Q

Main connections of septal nuclei

A

Afferent: Amygdala, olfactory tract, hippocampus, brainstem

Efferent: Stria medularis thalami, hippocampus, hypothalamus

NOT REALLY INVOLVED IN MESOLIMBIC PATHWAY THOUGH

31
Q

Outline mesolimbic pathway

A

Dopaminergic cells projecting from midbrain (ventral tegmental area, VTN) to the cortex, nucleus accumbens and amygdala.

Travel via the MFB (medial forebrain bundle)

32
Q

Relevance of mesolimbic pathway

A

Pathway from VTN to nucleus accumbens has increased dopamine release in drugs such as:

Opioids, nicotine, amphetamines, ethanol and cocaine all

33
Q

How do drugs affecting the mesolimbic pathway work.

Specifically how does cocaine work

A

Stimulate midbrain neurons, promote DA release or inhibit DA reuptake
Other neurotransmitters also modify this system
Cocaine inhibits reuptake of dopamine

34
Q

Problems for parkinsons treatment

A

usually start with L-DOPA, but when this wears off, you use

dopamine agonists for the nigra-striatal pathway…

BUT as an unwanted effect you get also increased dopamine to the nucleus accumbens through the mesolimbic pathway, which can lead to obsessive compulsive activity (i.e. online gambling)

35
Q

What are the functions of the medial and lateral olfactory stria

A

The olfactory tract travels posteriorly on the inferior surface of the frontal lobe. As the tract reaches the anterior perforated substance (an area at the level of the optic chiasm) it divides into medial and lateral stria:

Lateral stria – carries the axons to the primary olfactory cortex, located within the uncus of temporal lobe.
Medial stria – carries the axons across the medial plane of the anterior commissure, where they meet the olfactory bulb of the opposite side.

The primary olfactory cortex sends nerve fibres to many other areas of the brain, notably the piriform cortex, the amygdala, olfactory tubercle and the secondary olfactory cortex. These areas are involved in the memory and appreciation of olfactory sensations.

36
Q

Where are the hippocampi located

A

floor of the lateral ventricle..

37
Q

What does the hippocampus connect to and how

A

Connects to the mamillary bodies…. via the fornix which runs underneath the corpus collosum

38
Q

Outline the connection between the cingulate cortex and the hippocampus

A

Cingulate cortex –> cingulum bundle –> entorhinal cortex –> perforant pathway –> hippocampus

39
Q

Which areas of the brain are affected in alzheimers and which are not

A

ARE: atrophy of the temporal lobe…. hippocampus affected a lot (leading to memory loss)

Occipital lobe largely unaffected so visual symptoms not prevalnet

Primary somatosensory and motor cortices unaffected. (apart from dressing apraxia in the moderate stage due to some parietal cell damage)

40
Q

Where are mitral cell bodies located

A

Cell bodies are arranged in a thin mitral cell body layer between the granule cell layer and the external plexiform layer

41
Q

State the nuclei in the amygdala

A

Cortico-medial nuclei
Central nucleus
Basolateral nuclei

42
Q

Why is the olfactory nerve special

A

Because it contains basal cells which can regenerate, so you can get new neurons here over a life time.

However, with age, they can be lost faster than be replaced by the basal cells.

Loss of neurons here is not inevitable and may be associated with neurodegenerative disease.

43
Q

What is the limbic system

A

rim or limbus of cortex adjacent to corpus callosum and diencephalon

Structurally and functionally interrelated areas considered as a single functional complex

Neuro (16 decks)

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