Limbic System

Question 1

What is the limbic lobe?

Answer 1

The limbic lobe is part of the cortex and forms part of the limbic system

Question 2

Location of CN I?

Answer 2

Nasal epithelium (olfactory mucosa)

Question 3

Where is the olfactory bulb and tract outgrowths from?

Answer 3

Telencephalon

Question 4

What is the only sensory system to bypass the thalamus?

Answer 4

Olfactory

Question 5

The olfactory system is intimately invovled with the limbic system. How can this be seen?

Answer 5

Smell can trigger powerful emotions, memory and ANS responses

Question 6

What does the limbic lobe consist of?

Answer 6

1. Cingulate gyrus
2. Parahippocampal gyrus

Question 7

Where is the cingulate gyrus located?

Answer 7

Immediately below cingulate sulcus but above corpus callosum

Question 8

What is the isthmus of the cingulate gyrus continuous inferiorly with?

Answer 8

Parahippocampal gyrus

Question 9

In which lobe is the parahippocampal gyrus located?

Answer 9

In temporal lobe

Question 10

What is the uncus?

Answer 10

The uncus is an anterior extremity of the parahippocampal gyrus.

Question 11

The limbic system mediates the ‘HOME’ functions. What are these? Which part of the limbic system are they mediated by?

Answer 11

• Homeostasis e.g. BP, HR, temperature, hormones; mediated by the hypothalamus
  
  • Body temp too low = shivering
  • Body temp too high = sweating
• Olfaction; mediated by para-olfactory area
• Memory; mediated by hippocampus
• Emotion; mediated by amygdala

Question 12

What is the neocortex?

Answer 12

Involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, language and spatial reasoning. This is highly developed in humans.

Question 13

What is the cingulum? What type of fibres does it consist of?

Answer 13

• Bundle of white matter fibres underlying the cingulate gyrus
• Association fibres; connect cortical areas within the same hemispheres

Question 14

Function of cingulum?

Answer 14

• Receives information from pre-frontal, parietal, occipital, temporal gyri
• It is involved in the formation of memories and emotions

Question 15

What is the amygdala? Where is it located?

Answer 15

• Almond shaped nuclear (collection of cell bodies) complex in the medial temporal lobe
• Deep to the uncus

Question 16

Main function of amygdala in humans? How does this differ in animals?

Answer 16

• Mainly involved in emotions and behaviour
• Primitive role in survival in animals (not humans); stress responses, feeding, sexual behaviours
• Humans have neocortex so can rationalise (e.g. won’t kill to eat for survival)

Question 17

How can lesions of the amygdala present?

Answer 17

May affect patient’s evaluation of events, may lack emotions

Question 18

What is the hippocampal formation? Where is it located?

Answer 18

• Nuclear complex in the medial temporal lobe
• Deep to the parahippocampal gyrus

Question 19

Main function of hippocampal formation?

Answer 19

Mainly involved in memory (mainly short-term memories)

Question 20

How can lesions of the hippocampal formation present?

Answer 20

Single lesion capable of causing short-term memory loss but NOT long-term memory loss

Question 21

The cingulate gyrus, parahippocampal gyrus and uncus are bumpy (i.e. have something underneath them). What is found underneath each structure?

Answer 21

• Cingulate gyrus; bundle of white matter association fibres underneath (cingulum)
• Uncus; collection of grey matter cell bodies (amygdala)
• Parahippocampal gyrus; hippocampus

Question 22

What is the stria terminalis? What does it connect?

Answer 22

• C-shaped band of fibres that runs along the ventricular surface of the thalamus (in lateral ventricle)
• Is the outflow tract of the amygdala; connects it to the hypothalamus

Question 23

What does the fornix connect?

Answer 23

• Fornix; C-shaped tract that connects hippocampus to hypothalamus (including mamillary bodies)
  
  • Explains why emotions can trigger autonomic responses (e.g. increased HR)

Question 24

Why are the stria terminalis and fornix C-shaped?

Answer 24

Follow the curves of the lateral ventricles

Question 25

Connections of the amygdala:

Answer 25

* Unprocessed visual, auditory, somatosensory, gustatory, and olfactory stimuli * Cortex: cingulate and parahippocampal gyri * These are the majority of connections that reach the amygdala * Processed visual, auditory, somatosensory gustatory and olfactory stimuli * Connections are given meaning and context * Nuclei of ANS: Brainstem and Hypothalamus

Question 26

What does the hippocampal formation consist of?

Answer 26

Hippocampal formation refers to; dentate gyrus & hippocampus proper

Question 27

What does the hippocampal formation form the floor of?

Answer 27

The inferior horn of the lateral ventricles

Question 28

What structure contains the main efferent fibers of the hippocampus?

Answer 28

Fornix

Question 29

How do axons leave the hippocampal formation?

Answer 29

* Axons leave hippocampal formation via the **fimbria of fornix,** which is continuous with the crus, the body and then the columns of the fornix * The columns of the fornix reach the mamillary bodies (part of the hypothalamus)

Question 30

What is the hippocampal commissure?

Answer 30

allows for communication between fornices on each side

Question 31

Planes of dissection

Answer 31

Question 32

What is the Circuit of Papez? What structures does it involve?

Answer 32

* Closed, bidirectional circuit * Involves; * Hippocampus and adjacent cortex * Fornix * Mamillary bodies * Anterior nucleus of thalamus * Cingulum

Question 33

Function of circuit of papez?

Answer 33

* Important in reinforcement of emotion, memory and olfaction with each other for **survival responses** * Cortical control of emotion and memory storage

Question 34

Explain the circuit of papez pathway

Answer 34

Hippocampus --\> fornix --\> mamillary bodies --\> mammillothalamic fibres --\> thalamus (anterior nucleus) --\> cingulate gyrus/cingulum --\> hippocampal formation Once fibres are in the cingulate gyrus, they can be distributed to different parts of cortex e.g. prefrontal lobe, parietal area, visual association areas

Question 35

What are mamillothalamic fibres?

Answer 35

going from mamillary bodies to thalamus (anterior nucleus)

Question 36

Which part of the thalamus is invovled in the circuit of papez?

Answer 36

Anterior nucleus of thalamus

Question 37

What type of memory is the hippocampal formation involved in?

Answer 37

* **Short term memory** * Vital for the formation of new memories and learning * Damage leads to an inability to recall recent events (short-term memory) and learning * Memories of distant past and intelligence remain intact

Question 38

Where does the hippocampus receive info via (i.e. input)?

Answer 38

Via the **cingulum**: from many areas including cingulate gyrus and other cortical areas

Question 39

What is the major output tract of the hippocampus?

Answer 39

Fornix

Question 40

The fornix connects the hippocampus to the mamillary bodies of the hypothalamus. Where do the fibres pass after this?

Answer 40

* From **mammillary body**, fibres ascend to anterior nucleus of thalamus, fibres then project to cingulate gyrus (circuit of papez). * Then distributed to cortical areas including pre-frontal, posterior parietal and temporal association via the cingulum

Question 41

How is short term memory turned into long term memory?

Answer 41

When specific items of information are important to remember these items are **rehearsed repeatedly** until they are **permanently stored** in the areas of cortex associated with long-term memory

Question 42

Endocrine function of the hippocampal formation?

Answer 42

* Inputs to hypothalamus, modulatory role * Hypothalamus connected to pituitary

Question 43

What part of the brain is involved in short term memory?

Answer 43

Hippocampus

Question 44

What part of the brain is involved in long term memory?

Answer 44

Neocortex

Question 45

What is 'working memory'? What part of the brain is involved in this?

Answer 45

* Limited capacity that can hold information temporarily, important for reasoning and guidance of decision-making and behaviour e.g. exams * Hippocampus

Question 46

What is the limbic system? What 4 functions is it involved in?

Answer 46

Group of grey and white matter structures lodged deep within the cerebrum. Involved in; 1. Olfaction 2. Emotional responses 3. Behavioural activities 4. Memory

Question 47

What are the 2 main compenents of the **limbic lobe**?

Answer 47

1. Cingulate gyrus (at top) 2. Parahippocampal gyrus (at bottom, in temporal lobe)

Question 48

What is the parahippocampal gyrus mainly involved in?

Answer 48

Memory

Question 49

What 3 components makes up the hippocampal formation?

Answer 49

1. Dentate gyrus (**afferent** component of hippocampal formation) 2. Subiculum 3. Hippocampus proper

Question 50

1ary function of amygdala?

Answer 50

* Emotional responses (including response to smell) * Behaviours

Question 51

What are the 1ary grey matter components of the limbic system?

Answer 51

* Limbic lobe (cingulate gyrus & parahippocampal gyrus) * Hippocampal formation * Amygdala * Thalamus * Hypothalamus * Septal area * Habenula

Question 52

What is the septum pellucidum?

Answer 52

The septum pellucidum is a thin, triangular, vertical double membrane separating the anterior horns of the left and right lateral ventricles of the brain. It runs as a sheet from the corpus callosum down to the fornix

Question 53

What does the fornix connect?

Answer 53

Hippocampus --\> Hypothalamus (mamillary bodies)

Question 54

What is the major outflow tract of the amygdala? What does it connect?

Answer 54

**Striae terminalis**; amygdala --\> septal area + hypothalamus

Question 55

What is the septal area?

Answer 55

The septal area (medial olfactory area) is an area in the lower, posterior part of the medial surface of the frontal lobe, and refers to the nearby **septum** **pellucidum**. The septal nuclei are located in this area.

Question 56

Which tract/fibres connect the mamillary bodies to the anterior nucleus of the thalamus?

Answer 56

Mammillo-thalamic tract/fibres

Question 57

Function of the anterior nucleus of the thalamus?

Answer 57

display functions pertaining to memory

Question 58

What are the 2 directions that the circuit of Papez can take?

Answer 58

1. Hippocampus --\> fornix --\> mamillary bodies --\> mammillothalamic fibres/tract --\> thalamus (anterior nucleus) --\> cingulate gyrus/cingulum --\> **hippocampus** (via dentate gyrus – this is the afferent component) 2. Hippocampus --\> fornix --\> mamillary bodies --\> mammillothalamic fibres/tract --\> thalamus (anterior nucleus) --\> cingulate gyrus/cingulum --\> **pre-frontal cortex**

Question 59

Via which tract do fibres pass from the mamillary bodies to the anterior nucleus of the thalamus?

Answer 59

Mamillothalamic fibres

Question 60

Which nucleus of the thalamus is involved in the circuit of Papez?

Answer 60

Anterior nucleus

Question 61

Function of the involvement of the prefrontal cortex in the circuit of Papez?

Answer 61

To involve memory in thoughts and decision making