Limbic System Flashcards
Anosmia
- Loss of smell
- can be an early sign of neuroegeneration
What is the loss of smell sensation called?
Anosmia
How many smells can humans detect?
2000 - 4000 odours
-> molecular mechanisms of smelling are largely unknown
What are the components of the olfactory epithelium?
- bipolar olfactory neurons (from epithelium to olfactory bulb)
- sustentacular cells (support cells)
- basal cells (-> potential for production of new cells)
Does smell stay the same throughout life?
No, there is progressive loss of smell with age.
How do smells get transmitted to the brain?
- 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.
What are some causes of anosmia?
- midface trauma
- it is an early sign of neurodegenerative disease, e.g. PD
How do some people detect that they will have a seizure?
- 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
piriform cortex
- in the temporal lobe
- its function relates to smell
What is the limbic system?
structurally and functionally interrelated areas concidered as a single functional complex
What are the functions of the limbic system?
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)
What are the components of the limbic system?
- frontal lobe
- thalamus
- hippocampus
- amygdala
- hypothalamus
- olfactory bulb
LIMBUS in latin
= border
What is the fornix?
- 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
How does the paper circuit work?
- 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.
What changes occur in the brain in depression?
- 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
What are the main functions of the hippocampus?
- memory and learning
What are the main connections of the hippocampus?
- Afferent: Perforant pathway
- Efferent/output: Fimbria/ fornix
What are some clinical problems associated with the hippocampus?
Alzheimer’s disease, epilepsy
What is the difference between fimrbria and fornix?
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.
Where is the hippocampus?
on the medial temporal lobe
Where is the amygdala?
- 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
What are some structural changes in the brain that occur in Alzheimers?
- enlargement of the ventricles
- atrophy of the cortex -> brain shrinks
- atrophy of the hippocampus
- Tao – normal scaffolding within neurons is disturbed – tangles.
What are the 2 microscopic components of AD?
- tangles (in cell bodies of neurones?)
- plaques (protein pathology)
Anatomical preogression of AD
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
What are the main connections of the amygdala?
- Afferent: Olfactory cortex, septum, temporal neocortex, hippocampus, brainstem
- Efferent: Stria terminalis (= main output pathway, goes to more anterior parts of the hypothalamus)
What are the main functions fo the amygdala?
- fear and anxiety
- fight or flight
What are some clinical problems associated with the amygdala?
- 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.
Degeneration of the amygdala?
Different parts of the amygdala appear to have a different susceptibility to neurodegeneration.
Kluver-bucy-syndrome?
Syndrome originally described in monkeys with bilateral temporal lobectomy
- Hyperorality
- Loss of fear
- Visual agnosia
- Hypersexuality
Which structures in the brain are experimentally associated with aggression?
- Hypothalamus
- Brainstem (periaqueductal grey)
- Amygdala
5-HT in raphe nuclei (serotonin) is the main NT here
What are the main connections of the septal nuclei?
- Afferent: Amygdala, olfactory tract, hippocampus, brainstem
- Efferent: Stria medularis thalami, hippocampus, hypothalamus
What are the main functions of the septal nuclei?
Reward and reinforcement
Where are the septal nuclei?
- by the septum (membrane lying between lateral ventricles)
What is the mesolimbic pathway?
- 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.
What is the problem in PD?
- problem in the dopaminergic projections from substantia nigra to basal ganglia
What is the pathway in drug dependance?
- 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
What is the entorhinal cortex?
- 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
Stria terminalis
- 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.
