Neuro 14: Olfaction and limbic system

Question 1

Cells in the olfactory epithelium

Answer 1

bipolar olfactory neurons (primary olfactory neurone)

sustentacular cells (support cells)

basal cells (potential for regeneration… unique)

Question 2

Effect of age on smell

Answer 2

progressive loss with age

Question 3

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

Answer 3

olfactory receptor cells (bipolar)….

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

Question 4

Pathway for olfactory system

Answer 4

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)

Question 5

What is clinical deficit of smell

Answer 5

Anosmia

Question 6

Where is the piriform cortex

Answer 6

Temporal lobe (inferomedially)

Question 7

What is a prodromal aura

Answer 7

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

Question 8

Nose in parkinson’s

Answer 8

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

Question 9

Function of limbic system

Answer 9

Aimed at survival:
maintenance of homeostasis

agonistic (defence & attack) behaviour

sexual & reproductive behaviour

memory

or

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

Question 10

How does limbic system help to achieve homeostasis

Answer 10

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

Question 11

Components of limbic system

Answer 11

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

Question 12

What is the Papaz ciruit

Answer 12

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

Question 13

Which structure achieves the following:

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

Answer 13

neocortex,
cingulate cortex
hypothalamus

Question 14

Connections of hippocampus

Answer 14

Afferent: Perforant pathway
Efferent: Fimbria (=fornix)

Question 15

Function of hippocampus

Answer 15

memory and learning

Question 16

Clinical conditins involving problems with hippocampus

Answer 16

Alzheimer’s (short term memory loss), epilepsy

Question 17

Where do the hippocampi sit

Answer 17

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

Question 18

Where does the fornix project

Answer 18

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

Question 19

Where does the amygdala sit

Answer 19

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

Question 20

Where does the perforant pathway come from

Answer 20

entorhinal cortex

Question 21

Signs of alzheimer’s

Answer 21

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

Question 22

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

Answer 22

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

Question 23

Outline the anatomical progression of Alzheimer’s

Answer 23

Early
Hippocampus and entorhinal cortex
Short-term memory problems

Moderate
Parietal lobe
Dressing apraxia

Late
Frontal lobe
Loss of executive skills

Question 24

Connections of the amygdala

Answer 24

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

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

Question 25

Function of amygdala

Answer 25

Fear & anxiety | Fight or flight

Question 26

In which clinical situituation is amygdala implicated

Answer 26

Kluver-Bucy syndrome

Question 27

Symptomy of kluver bucy

Answer 27

Hyperorality Loss of fear Visual agnosia Hypersexuality Sex Mouth Agnosia Loss of fear (due to bilateal temporal lobe contusion)

Question 28

Strcutures related to aggression

Answer 28

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

Question 29

What is the septal nuclei

Answer 29

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

Question 30

Main connections of septal nuclei

Answer 30

Afferent: Amygdala, olfactory tract, hippocampus, brainstem Efferent: Stria medularis thalami, hippocampus, hypothalamus NOT REALLY INVOLVED IN MESOLIMBIC PATHWAY THOUGH

Question 31

Outline mesolimbic pathway

Answer 31

Dopaminergic cells projecting from midbrain (ventral tegmental area, VTN) to the cortex, nucleus accumbens and amygdala. Travel via the MFB (medial forebrain bundle)

Question 32

Relevance of mesolimbic pathway

Answer 32

Pathway from VTN to nucleus accumbens has increased dopamine release in drugs such as: Opioids, nicotine, amphetamines, ethanol and cocaine all

Question 33

How do drugs affecting the mesolimbic pathway work. Specifically how does cocaine work

Answer 33

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

Question 34

Problems for parkinsons treatment

Answer 34

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)

Question 35

What are the functions of the medial and lateral olfactory stria

Answer 35

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.

Question 36

Where are the hippocampi located

Answer 36

floor of the lateral ventricle..

Question 37

What does the hippocampus connect to and how

Answer 37

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

Question 38

Outline the connection between the cingulate cortex and the hippocampus

Answer 38

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

Question 39

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

Answer 39

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)

Question 40

Where are mitral cell bodies located

Answer 40

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

Question 41

State the nuclei in the amygdala

Answer 41

Cortico-medial nuclei Central nucleus Basolateral nuclei

Question 42

Why is the olfactory nerve special

Answer 42

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.

Question 43

What is the limbic system

Answer 43

rim or limbus of cortex adjacent to corpus callosum and diencephalon Structurally and functionally interrelated areas considered as a single functional complex