Limbic System

Question 1

Anosmia

Answer 1

• Loss of smell

- can be an early sign of neuroegeneration

Question 2

What is the loss of smell sensation called?

Answer 2

Anosmia

Question 3

How many smells can humans detect?

Answer 3

2000 - 4000 odours

-> molecular mechanisms of smelling are largely unknown

Question 4

What are the components of the olfactory epithelium?

Answer 4

• bipolar olfactory neurons (from epithelium to olfactory bulb)
• sustentacular cells (support cells)
• basal cells (-> potential for production of new cells)

Question 5

Does smell stay the same throughout life?

Answer 5

No, there is progressive loss of smell with age.

Question 6

How do smells get transmitted to the brain?

Answer 6

• bipolar neurones from olfactory epithelium travel through cribriform in ethmoid bone
• synapse in the olfactory bulb with 2nd order neurones that make up the olfactory tract
• the olfactory tracts split into stria, one connecting to the piriform complex the other connecting to the orbitofrontal cortex
• there are also some connections to the brainstem -> salivation
• molecular mechanisms of small are not known.

Question 7

What are some causes of anosmia?

Answer 7

• midface trauma

- it is an early sign of neurodegenerative disease, e.g. PD

Question 8

How do some people detect that they will have a seizure?

Answer 8

• some poeple sense a certain smell hat they associate with having a seizure
• a lot of epilepsy is associated with the temporal lobe = prodromal aura

Question 9

piriform cortex

Answer 9

• in the temporal lobe

- its function relates to smell

Question 10

What is the limbic system?

Answer 10

structurally and functionally interrelated areas concidered as a single functional complex

Question 11

What are the functions of the limbic system?

Answer 11

System responsible for processes aimed at survival of the individual:

• maintenance of homeostasis via activation of visceral effector mechanisms, modulation of pituitary hormone release and initiation of feeding and drinking
• agonistic (defence & attack) behaviour (-> fight or flight)
• sexual & reproductive behaviour
• memory (memory is a huge part of emotional processing)

Question 12

What are the components of the limbic system?

Answer 12

• frontal lobe
• thalamus
• hippocampus
• amygdala
• hypothalamus
• olfactory bulb

Question 13

LIMBUS in latin

Answer 13

= border

Question 14

What is the fornix?

Answer 14

• c-shaped bundle fo nerve fibres that go from the hippocampus to the mammilary bodies of the hypothalamus and from there to the thalamus
• also connects Hippocampus to the septal nuclei and nucleus accumbens

Question 15

How does the paper circuit work?

Answer 15

• There are projections from the hippocampus to the mammillary bodies of the thalamus called the fornix)
• the hypothalamus is the main component of emotional expression / reaction
• through he MTT (mamillo-thalamic-tract) signals go from the hypothalamus to the anterior nucleus of the thalamus
• the anterior nucleus of the thalamus sends ifs to the consulate cortex.
• the cingulate cortex has input from the neocortex (emotional colouring based on experiences). The neocortex feeds into the circuit.

Question 16

What changes occur in the brain in depression?

Answer 16

• there are no anatomical changes, post-mortems do not reveal anything
• there are functional changes that can be seen in e.g. diffusion tensor imaging

Question 17

What are the main functions of the hippocampus?

Answer 17

• memory and learning

Question 18

What are the main connections of the hippocampus?

Answer 18

• Afferent: Perforant pathway

- Efferent/output: Fimbria/ fornix

Question 19

What are some clinical problems associated with the hippocampus?

Answer 19

Alzheimer’s disease, epilepsy

Question 20

What is the difference between fimrbria and fornix?

Answer 20

It is the same pathway. When it is physically attached to the hippocampus its the fimbria, as soon as it detaches it is called the fornix.

Question 21

Where is the hippocampus?

Answer 21

on the medial temporal lobe

Question 22

Where is the amygdala?

Answer 22

• in the white matter of the temporal lobe
• lying in front of the hippocampus
• it is a grey matter nucleus embedded in the white matter of the temporal lobe.
• different parts of the amygdala are more susceptible to neurodegeneration

Question 23

What are some structural changes in the brain that occur in Alzheimers?

Answer 23

• enlargement of the ventricles
• atrophy of the cortex -> brain shrinks
• atrophy of the hippocampus
• Tao – normal scaffolding within neurons is disturbed – tangles.

Question 24

What are the 2 microscopic components of AD?

Answer 24

• tangles (in cell bodies of neurones?)

- plaques (protein pathology)

Question 25

Anatomical preogression of AD

Answer 25

Early - Hippocampus and entorhinal cortex - Short-term memory problems Moderate - disease spreading to parietal lobe - Dressing apraxia Late - Frontal lobe - Loss of executive skills, personality change => there is a fairly predictable course

Question 26

What are the main connections of the amygdala?

Answer 26

- Afferent: Olfactory cortex, septum, temporal neocortex, hippocampus, brainstem - Efferent: Stria terminalis (= main output pathway, goes to more anterior parts of the hypothalamus)

Question 27

What are the main functions fo the amygdala?

Answer 27

- fear and anxiety | - fight or flight

Question 28

What are some clinical problems associated with the amygdala?

Answer 28

- Kluver-Bucy syndrome: has a number of features including a more basic view of the world, hyperorality, heightened fear, oral tendencies, memory loss, emotional changes, extreme sexual behavior - can be caused by lesions (e.g. trauma or infections) in the temporal lobe.

Question 29

Degeneration of the amygdala?

Answer 29

Different parts of the amygdala appear to have a different susceptibility to neurodegeneration.

Question 30

Kluver-bucy-syndrome?

Answer 30

Syndrome originally described in monkeys with bilateral temporal lobectomy - Hyperorality - Loss of fear - Visual agnosia - Hypersexuality

Question 31

Which structures in the brain are experimentally associated with aggression?

Answer 31

- Hypothalamus - Brainstem (periaqueductal grey) - Amygdala 5-HT in raphe nuclei (serotonin) is the main NT here

Question 32

What are the main connections of the septal nuclei?

Answer 32

- Afferent: Amygdala, olfactory tract, hippocampus, brainstem - Efferent: Stria medularis thalami, hippocampus, hypothalamus

Question 33

What are the main functions of the septal nuclei?

Answer 33

Reward and reinforcement

Question 34

Where are the septal nuclei?

Answer 34

- by the septum (membrane lying between lateral ventricles)

Question 35

What is the mesolimbic pathway?

Answer 35

- it is a dopaminergic pathway - reward pathway - originates in the midbrain (VTA) - travels to NAcc, cortex and amygdala via MFB (median forebrain bundle) - different than the nigrostriatal dopaminergic pathway that is affected in PD.

Question 36

What is the problem in PD?

Answer 36

- problem in the dopaminergic projections from substantia nigra to basal ganglia

Question 37

What is the pathway in drug dependance?

Answer 37

- projectionstions from ventral tegmental area to cortex, amygdala and nucleus accumbens - Opioids, nicotine, amphetamines, ethanol and cocaine all increase DA release in nucleus accumbens - Stimulate midbrain neurons, promote DA release or inhibit DA reuptake - Other neurotransmitters also modify this system - thought to be the basis of addiction - constant DOPAMINE release => mesolimbic pathway - reward pathway

Question 38

What is the entorhinal cortex?

Answer 38

- area of the brain in the medial temporal lobe - Functions: memory, navigation, perception of time - main interface between the neocortex and the hippocampus - important for declarative memories (e.g. autobiography, semantic, episodic memories) and particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep

Question 39

Stria terminalis

Answer 39

- Efferent pathway of the amygdala - goes to more anterior parts of the hypothalamus - Durch die Stria terminalis verlaufen Projektionen zum Hirnstamm, insbesondere zum Kreislauf-, Atem- und Brechzentrum in der Formatio reticularis. Sie wird aktiviert bei Anspannung, Stress und Sexualität.