Olfaction and the Limbic System

Question 1

What the three types of cell that makes up the olfactory epithelium?

Answer 1

Bipolar Olfactory Neurones

Sustentacular Cells – support cells mainly providing metabolic support

Basal Cells – there is some regeneration in olfactory neurones

Question 2

Where is the olfactory bulb found?

Answer 2

Sitting on top of the cribriform plate

Question 3

Which cells synapse within the olfactory bulb?

Answer 3

The bipolar cells pass their axons through the cribriform plate to synapse with the second order neurones (olfactory bulb mitral cells) in the glomerulus within the olfactory bulb

Question 4

What structure do the second order neurones form and what does this structure split into?

Answer 4

Olfactory tract

It splits to form the medial and lateral olfactory stria

Question 5

Where does higher processing of smell take place?

Answer 5

Piriform Cortex

Orbitofrontal Cortex

Question 6

What is a clinical deficit in the olfactory system called?

Answer 6

Anosmia- lack of smell

Question 7

What is a common cause of anosmia?

Answer 7

Mid-face trauma

Impact with enough force could cause a fracture of the cribriform plate, shearing the neurones going from the olfactory epithelium to the olfactory bulb

Question 8

The piriform cortex is found within the temporal lobe. Explain thesignificance of this with regards to epileptic patients.

Answer 8

Epilepsy is often focused in the temporal lobe

This means that some people with epilepsy will experience PRODROMAL AURA (they are made aware of an imminent seizure because they’ll smell something that’s not there)

Question 9

Neurodegenerative disease is a relatively common cause of anosmia.

State two neurodegenerative diseases that could cause anosmia.

Answer 9

Alzheimer’s disease

Parkinson’s disease

Question 10

What is the limbic system?/ what makes it up

Answer 10

A rim of cortex adjacent to the corpus callosum and diencephalon, responsible for general survival instinct

composed of olfactory bulbs, hypothalamus, amygdala, hippocampus, thalamus and frontal lobe

Question 11

What are the roles of the limbic system?

Answer 11

general survival instinct:

• Homeostasis (mainly hypothalamic functions such as regulation of food intake and pituitary hormone release)
• Agonistic behaviour (fight or flight)
• Sexual and reproductive behaviour
• Memory

Question 12

State two important parts of the limbic system that are found within the temporal lobes.

Answer 12

Hippocampus and Amygdala

Question 13

What circuit are these structures (Hippocampus and Amygdala) a part of?

Answer 13

Papez Circuit

Question 14

What is the cortical representation of the limbic system?

Answer 14

Cingulate Cortex

Question 15

What is the function of the Papez circuit?

Answer 15

It is a neural circuit for the control of emotional expression

Question 16

Describe/draw the papez circuit.

Answer 16

Hippocampus —via Fornix —> Mammillary Bodies of hypothalamus —via Mammillo-Thalamic Tract (MTT) —> Anterior Nucleus of the Thalamus –> Cingulate Cortex — via Cingulum Bundle —> Hippocampus

Question 17

What conditions could damage the mammillary bodies leading to amnestic issues?

Answer 17

Chronic Alcoholism

Wernicke-Korsakoff Syndrome

Question 18

What is our emotional expression ‘coloured’ by?

Answer 18

Neocortex- ie contributes past experiences/ previous memory

Question 19

What form of imaging is used to study the limbic system?

Answer 19

Digital Tensor Imaging – shows co-instant activity in different parts of the brain thus showing which parts of the brain are working together

Question 20

Describe the afferent pathway of the hippocampus.

Answer 20

Afferent Pathway = Perforant Pathway

The entorhinal cortex is linked to the hippocampus via the afferent pathway (perforant pathway)
The entorhinal cortex receives input from all other parts of the neocortex

Question 21

What is the efferent pathway of the hippocampus called?

Answer 21

Fimbria/Fornix

Question 22

What are the functions of the hippocampus?

Answer 22

Memory and Learning

Question 23

What happens to the hippocampus in Alzheimer’s disease?

Answer 23

It shrinks severely

Question 24

Describe the spatial relations of the hippocampus and the fornix to other important brain structures.

Answer 24

The hippocampus is found on the floor of the lateral ventricles

The fornix comes out of the hippocampus and passes under the corpus callosum

It then dives inferior and anteriorly towards the mammillary bodies

Question 25

Describe the appearance of advanced Alzheimer’s disease on a CT head scan in the coronal plane.

Answer 25

There will be extensive cortical atrophy The ventricles would appear enlarged There will also be widening of sulci

Question 26

State two microscopic hallmarks of neurodegeneration.

Answer 26

Tau Immunostaining  Intracellular pathology – the cytoskeleton has been compromised  The tau proteins show up in the staining and allow the damaged neurones to be seen Senile Plaques  Extracellular pathology  Lumps of protein (alpha-beta proteins) sitting in between cells in the neuropil

Question 27

Describe the anatomical progression of Alzheimer’s disease, including the symptoms experienced.

Answer 27

Early  Hippocampus and entorhinal cortex affected  Short-term memory problems Moderate  Parietal lobe affected (where you have your procedural memory)  Example of effects: dressing apraxia Late  Frontal lobe  Loss of executive skills

Question 28

Where is the amydala found?

Answer 28

In the white matter of anterior temporal lobe

Question 29

What are the afferent connections of the amygdala?

Answer 29

Olfactory Cortex Septum (septal nuclei) Temporal Neocortex Hippocampus Brainstem

Question 30

What is the main output pathway (efferent) of the amygdala?

Answer 30

Stria terminalis

Question 31

What is the function of the amygdala?

Answer 31

Fear and Anxiety fight or flight

Question 32

In Alzheimer’s and Parkinson’s disease, the amygdala starts showing pathology early on. What are the possible outcomes of this?

Answer 32

Patients could either become terrified of everything or they could become totally disinhibited and become quite aggressive

Question 33

State and describe a syndrome affecting the amygdala.

Answer 33

``` Kluver-Bucy Syndrome Bilateral lesions of the anterior temporal lobe (including amygdaloid nucleus) Symptoms :  Hyperorality  Hypersexuality  Loss of Fear  Visual Agnosia ```

Question 34

State three structures associated with aggression.

Answer 34

Hypothalamus Brainstem (periaqueductal grey matter) Amygdala

Question 35

What are the main afferent connections of the septum?

Answer 35

Amygdala Olfactory Tract Hippocampus Brainstem

Question 36

What are the functions of the septum?

Answer 36

Reinforcement and Reward

Question 37

Name another structure that is important in the reward system.

Answer 37

Nucleus Accumbens

Question 38

Name a structure that is important in drug dependence.

Answer 38

Nucleus Accumbens

Question 39

What effect do all drugs of abuse have on the nucleus accumbens?

Answer 39

They all increase dopamine release in the nucleus accumbens

Question 40

what is the mesolithic pathway

Answer 40

Ventral tegmental area (midbrain --> Nucleus accumbens | via MFB- median forebrain bundle

Question 41

which drugs increase dopamine in the nucleus accumbens

Answer 41

``` opiods nicotine amphetamines ethanol cocaine ```