Lec 40 Limbic System Anatomy

Question 1

What are the four main components of limbic system?

Answer 1

1. limbic cortex [limbic lobe + prefrontal cortex]
2. subcortical structs: amygdala, hippocampal formation, thalamic nuclei, habenular nuclei
3. cholinergic cells of basal forebrain and septal nuclei
4. DA reward paths

Question 2

What is function of limbic system?

Answer 2

memory
emotion
motivational drive
homeostasis

Question 3

What 4 structures comprise limbic lobe?

Answer 3

• cingulate gyrus
• isthmus
• parahippocampal gyrus
• subcallosal/subgenual gyri

Question 4

What are the major functions of prefrontal cortex?

Answer 4

• attention; concentration; executive control; cognition; planning; working memory; decision making

emotion; motivation; personality

Question 5

What happens if damage to PFC?

Answer 5

behavioral disinhibition = individuals show exaggerated impulsivity and compulsivity

implicated in dementia and most psychiatric syndromes –> schizophrenia, depression, ADD

Question 6

What is function of cingulum?

Answer 6

fiber bundle that contains major efferents from cingulate cortex

learn to correct mistakes + reinforce behaviors that reduce pain

Question 7

What are the major outputs of cingulate cortex?

Answer 7

• to subicular and entorhinal cortex [temporal lobe]
• to association neocortex/ventral striatum/thalamic nuclei
• to amygdala, hypothalamis

Question 8

What is function of cingulate gyrus?

Answer 8

learn to correct mistakes/reinforce behaviors that reduce pain

–> receives pain/temp input from spinothalamic tract and outputs to temporal lobe

Question 9

What is the entorhinal cortex?

Answer 9

• inferior surface of parahippocampal gyrus

- major afferents to hippocampal formation pass through it

Question 10

What are two main parts of the hippocampal formation?

Answer 10

hippocampus proper [ = cornu ammonis fields 1-4]

and dentate gyrus

Question 11

What is the subiculum?

Answer 11

output structure of the hippocampal formation

Question 12

What is function of hippocampus?

Answer 12

formation of new declarative memories [but not storage]

Question 13

What happens if lesion of hippocampal formation?

Answer 13

anterograde amnesia = can recall old memories but can’t make new ones

Question 14

What is contained in dentate nucleus?

Answer 14

granule cells

Question 15

What is contained in CA region?

Answer 15

large pyramidal neurons

Question 16

What type of neurons in main circuit of hippocampus?

Answer 16

glutamate

Question 17

What is major input to hippocampal formation?

Answer 17

entorhinal cortex –> dentate gyrus

Question 18

What does dentate gyrus project to?

Answer 18

CA3

Question 19

What is path of internal processing of inputs to hippocampal formation?

Answer 19

entorhinal cortex –> dentate gyrus –> via mossy fibers to CA3 –> via shcaefer collaterals to CA1 –> to subiculum –> post-commissural fornix –> mammillary bodies

majority CA3 also:
–> pre-commissural fornix –> nucleus accumbens septi

Question 20

What are inputs to hippocampal formation via entorhinal cortex?

Answer 20

• association cortices [limbic regions of temporal/frontal]
• ACh from basal forebrain and septal nuclear region
• subcortical inputs from amygdala and thalamus

Question 21

What are schaffer collaterals?

Answer 21

fiber system of CA3 collaterals that go to CA1

Question 22

What is major output structure of hippocampus? to where?

Answer 22

subiculum sends output via fornix to many areas [hypothalamus, mamillary, septal nuc. NAc, PFC]

Question 23

What is implicated in “timing” of memories?

Answer 23

adult hippocampal neurogenesis of granule neurons in the dentate gyrus

Question 24

Alzheimers is associated with degeneration of what input to hippocampal function?

Answer 24

azlheimers associated with degeneration of ACh neurons from septal nuclei that promote glu circuits in hippocampal formation

Question 25

What are limbic inputs to mammillary bodies of hypothalamus?

Answer 25

- from subiculum via postcommissural fornix | - from VTA DA neurons

Question 26

What is main output from mammillary bodies?

Answer 26

to thalamus anterior group and MD

Question 27

What are major inhibitory and excitatory control of HPA axis?

Answer 27

inhibitory: hippocampus excitatory: amygdala

Question 28

What happens to temporal lobe hippocampal formation in alzheimers?

Answer 28

atrophy

Question 29

What are symptoms of fronto-temporal dementia?

Answer 29

dramatic changes personality, socially inappropriate behavior, impulsivity, emotional indifference, language deficits

Question 30

What are hippocampal place cells? what happens if damaged?

Answer 30

cells responsible for cognitive map of external environment trouble path finding, localizing self in external space

Question 31

Where do pre-commisure fornix projections from hippocampal formation go? what about post-commisure?

Answer 31

``` pre-commisure = septal nuclei post-commisure = mammillary bodies ```

Question 32

How does acute high glucocorticoids affect hippocampus?

Answer 32

enhances inhibitory control over HPA axis [negative feedback]

Question 33

how does chronic high glucocorticoids affect hippocampus?

Answer 33

damages hippocampus --> disruption feedforward HPA inhibition --> continued HPA output --> further hippocampal damage this may be one mech by which sustained high level stress can increase risk for stress-related illnesses

Question 34

What is function of lateral habenula?

Answer 34

receives input from basal forebrain for mood regulation sends outputs throughout limbic cortex, thalamus, hypothalamus, brainstem

Question 35

Where do mammillary bodies project?

Answer 35

thalamus [anterior group] --> which then project back to cingulate cortex

Question 36

What paart of brain degenerates in korsakov dementia?

Answer 36

mamillary bodies and anterior group of thalamus

Question 37

What is importance of ACh innervation from septal nuclei to hippocampus?

Answer 37

cognition as related to path finding

Question 38

What is the function of amygdala?

Answer 38

associative memory = associating neutral cue with reward or punishmnt = fear conditioning

Question 39

What is kluver-bucy syndrome?

Answer 39

bilateral lesion of amygdala leads to absence of fear, placidity, hyperphagia, hypersexuality

Question 40

What are outputs of amygdala?

Answer 40

basolateral amygdala --> PFC, hippocampus, striatum central amygdala --> PAG, monoamine nuclei, HPA axis = major excitatory control of HPA axis = ANS

Question 41

What are two main output paths from amygdala?

Answer 41

ventral amygdalo-fugal path | stria terminalis

Question 42

What is function of ventral amygdalo-fugal path?

Answer 42

projects from amygdala to basal forebrain, hypothalamus, ventral striatum, thalamus

Question 43

What is function of the stria terminalis?

Answer 43

carries reciprocal connections between centromedial amygdala and hypothalamus - excitatory projection to HPA axis to regulate stress hormone response project to hypo regions important for control of eating, sex, HPA also projects to septal nuclei and thalamus

Question 44

What is function of bed nucleus of stria terminalis?

Answer 44

bed = sex

Question 45

What is the mesolimbic path? function?

Answer 45

DA path from VTA to nucleus accumbens septi [and amygdala, hippocampus, bed nucleus, septal nuclei] via MFB [median forebrain bundle] function = responds to reward and punishment VTA --> NAS --> VP --> MD

Question 46

What is the mesocortical path? function?

Answer 46

dopamine path from VTA to dorsal lateral prefrontal cortex, ventro medial prefrontal cortex, cingulate cortex, olfactory bulb = cognition/motivation/emotional responses