limbic system

Question 1

list the structural components of the limbic system (cortices, fibre tracts, nuclei)

Answer 1

cortices:
• cingulate gyrus
• parahippocampal gyrus
• orbitofrontal cortex
• subcallosal area
• hippocampal formation (hippocampus proper + dentate gyrus + entorhinal cortex + subiculum)

fibre tracts:
• fornix
• hipopcampal commisure
• cingulum
• unicate fascicle

nuclei:
• amygdala
• hypothalamus
• mammillary bodies
• anterior nucleus of thalamus

Question 2

where is the cingulum located and what does it connect?

Answer 2

located in cingulate and parahippocampal gyri

connects temporal part and cingulate gyrus

Question 3

what is connected by the unicate fascicle?

Answer 3

connects temporal lobe (amygdala) with orbitofrontal cortex (rational thought)

Question 4

how is memory stored long-term?

Answer 4

short-term memories are rehersed

eventually encoded into long-term memory via hippocampal formation

Question 5

what are the different components of long-term memory?

Answer 5

1) EXPLICIT / DECLARATIVE
• episodic memory (personally experienced events) → stored in most association cortical areas
• semantic memory (facts and general knowledge) → stored in most association cortical areas

2) IMPLICIT / NON-DECLARATIVE
• memories of skills + habits → stored in motor cortex, basal ganglia and cerebellum
• memories of emotions (classical and operant conditioning, priming) → mostly in amygdala

Question 6

what is the limbic circuit?

Answer 6

hippocampus → MB via fornix

MB → anterior nucleus of thalamus via mammilothalamic tract

thalamus → vingulate cortex via thalamocortical tract

cingulate → entorhinal cortex via cingulum

entorhinal cortex → dentate gyrus via perforant pathway

dentate gyrus → hippocampus via mossy fibre tracts

Question 7

in the development of alzheimers disease, which site is first affected?

Answer 7

the entorhinal cortex is the first site to be affected

observe beta-amyloid accumulation

Question 8

describe the function of the hippocampus

Answer 8

contains place-neurons that help map and remember places

contain time-neurons that help remember the flow of events in distinct experiences

transfers short-term memory to long-term memory

Question 9

describe the symptoms of HM after his bilateral removal hippocampi

Answer 9

long-term memory intact

short-term memory relatively intact

could not retain new memories i.e. could not transfer from short-term to long-term memory

profound anterograde amnesia

neurogenesis continues in adult hippocampus to facilitate learning and memory

Question 10

draw a diagram of the hippocampus proper

Answer 10

:)

Question 11

what areas of the hippocampus are particularly sensitive to:
– hypoxia
– seizure

Answer 11

CA1 is very sensitive to hypoxia

CA2 is very sensitive to seizure

Question 12

which structures are connected by the fornix?

Answer 12

hippocampus and mammillary body are connected by the thalamus

Question 13

what happens when the mammillary bodies are damaged?

Answer 13

alcoholism or malnutrition can lead to vitamin B1 deficiency

vitamine B1 deficiency damages the mammillary bodies, leading to Wenicke-Korsakoff syndrome

results in damage to limbic circuit and memory loss

Question 14

what is the function of the amygdala?

Answer 14

the amygdala analyses environmental stimuli for emotional significance to generate appropriate response

develop emotional attachment to stimulus
OR
generates perception of fear (flight or fight) via hypothalamus