Limbic System

Question 1

What are the cortical structures of the limbic system?

Answer 1

parahippocampal, cingulate, dentate gyri, hippocampus, subiculum, entorhinal cortex and orbitofrontal cortex

Question 2

What are the nuclei of the limbic system?

Answer 2

hypothalamus (including mammillary body), amygdala, anterior nucleus of the thalamus

Question 3

What are the fibre tracts of the limbic system?

Answer 3

fornix (including fimbria of hippocampus) and fornical (hippocampal) commissure, cingulum, uncinate fascicle

Question 4

What is the limbic lobe (Broca’s concept) and what is it composed of?

Answer 4

• The limbic lobe (Broca’s concept) is mainly an anatomical concept restricted to the cortical mantle of the telencephalon (not subcortical nuclei or fibre systems) that surrounds (borders) the diencephalon
• Broca’s limbic lobe is composed of the fornicate gyrus (cingulate gyrus + parahippocampal gryus) fornicate gyrus (from latin: fornicates=arched)

Question 5

What is the function of limbic structures?

Answer 5

linked with:

• Learning and memory
• Control of emotions and instinctive behaviour

Question 6

What is the concept of the limbic structures?

Answer 6

• Analyses stimuli (sensory input) for emotional significance
• Stores emotional memory
• Tags/colours sensory input with emotional component and impacts cognitive responses that is required for normal social behaviour and survival

Question 7

What is the cingulum and uncinate fascicle?

Answer 7

cingulum: is located in cingulate and parahippocampal gyri and connects cortical structures of both gyri
uncinate fascicle: connects temporal with frontal lobe (orbitofrontal cortex)

Question 8

Describe the location and features of the parahippocampal gyrus.

Answer 8

• It is located in basal medial temporal lobe
• It contains, in its anterior portion, the entorhinal cortec and uncus (the ‘hook’)
• Deep inside, it houses the subiculum, hippocampus and denate gyrus
• Posteriorly, it is continuous with the lingual gyrus (no clear identifiable border between the two gyri)

Question 9

Describe features of the hippocampus.

Answer 9

• The anterior portion of the hippocampus and its posterior part narrows (comma-like structure)
• It is approximately 4-5cm in length and divided into head, body and tail
• It lies in the floor of the inferior horn of the lateral ventricle
• It is located in mediobasal part of the temporal lobe deep inside the parahippocampal gryus

Question 10

What is the hippocampus an important structure for?

Answer 10

• Declarative (explicit) memory (e.g. history and facts)
• Contains so-called place neurones that help to map and remember places (spatial memory; navigation)
• Contains so-called time neurones that help to remember the flow of events in distinct experiences
  It transfers short-term memory (specifically the ‘when’ and ‘where’ of memory) into the long-term memory (‘key board’ versus ‘hard disk’ analogy)

Question 11

What does the hippocampal formation consist of?

Answer 11

hippocampus proper + dentate gyrus + entorhinal cortex + subiculum

Question 12

What is the limbic circuit order?

Answer 12

see diagram in notes

Question 13

Describe the structures of parahippocampal gyrus.

Answer 13

• The anterior portion of parahippocampal gyrus contains the entorhinal cortex and the uncus
• The subiculum and dentate gyrus (looks like teeth row) are visible deep inside the parahippocampal gyrus
• The uncus contains the semilunar gyri (amygdala is found deep inside the semilunar gyrus)

Question 14

Describe the structures of the fornix gyrus.

Answer 14

• The fornix (yellow) stretches as a C-shaped bundle of neuronal fibres below the corpus callosum (blue)
• The fornix connects each hippocampus with one mammillary body (of the hypothalamus)
• The two fornices (or two hippocami) are interconnected by the fornical (hippocampal) commissure
• The septum pellucidum (red) spans between the fornix (yellow) and the corpus callosum (blue)
• Septum pellucidum is a vertically oriented membrane that separates the two lateral verticles

Question 15

Describe the mamillary bodies.

Answer 15

• Are a pair of small round bodies on the basal surface of the brain
• Are posterior part of the hypothalamus
• Are considered as part of the limbic system

Question 16

Describe the functions and locations of the amygdala.

Answer 16

Amygdala is located in the medial portion of the temporal lobe, just rostral to the hippocampus and inside the uncus (semilunar gyrus).
Functions of amygdala:
- It analyses environmental stimuli for emotional significance (friendly or hostile) to generate appropriate responses; for instance:
o If friendly, it is able to develop emotional attachment to stimulus
o If hostile, it generates perception of fear and may triggers ‘fight or flight’ responses via hypothalamus (‘danger (detector) alarm system of the body’)
- Stores emotional memories of fear

Question 17

How does the hippocampal formation receive major input and send major output?

Answer 17

entorhinal cortex

Question 18

Describe the limbic circuit.

Answer 18

see image

Question 19

What is the Wernicke-Korsakoff syndrome?

Answer 19

damage to the mammillary bodies due to deficiency of vit-B1 which could be a result from chronic alcoholism or severe malnutrition

Question 20

What cortex relates to Alzheimers Disease?

Answer 20

entorhinal cortex