Limbic System Flashcards
What is the limbic lobe?
The limbic lobe is part of the cortex and forms part of the limbic system
Location of CN I?
Nasal epithelium (olfactory mucosa)
Where is the olfactory bulb and tract outgrowths from?
Telencephalon
What is the only sensory system to bypass the thalamus?
Olfactory
The olfactory system is intimately invovled with the limbic system. How can this be seen?
Smell can trigger powerful emotions, memory and ANS responses
What does the limbic lobe consist of?
- Cingulate gyrus
- Parahippocampal gyrus
Where is the cingulate gyrus located?
Immediately below cingulate sulcus but above corpus callosum
What is the isthmus of the cingulate gyrus continuous inferiorly with?
Parahippocampal gyrus
In which lobe is the parahippocampal gyrus located?
In temporal lobe
What is the uncus?
The uncus is an anterior extremity of the parahippocampal gyrus.
The limbic system mediates the ‘HOME’ functions. What are these? Which part of the limbic system are they mediated by?
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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
What is the neocortex?
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.
What is the cingulum? What type of fibres does it consist of?
- Bundle of white matter fibres underlying the cingulate gyrus
- Association fibres; connect cortical areas within the same hemispheres
Function of cingulum?
- Receives information from pre-frontal, parietal, occipital, temporal gyri
- It is involved in the formation of memories and emotions
What is the amygdala? Where is it located?
- Almond shaped nuclear (collection of cell bodies) complex in the medial temporal lobe
- Deep to the uncus
Main function of amygdala in humans? How does this differ in animals?
- 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)
How can lesions of the amygdala present?
May affect patient’s evaluation of events, may lack emotions
What is the hippocampal formation? Where is it located?
- Nuclear complex in the medial temporal lobe
- Deep to the parahippocampal gyrus
Main function of hippocampal formation?
Mainly involved in memory (mainly short-term memories)
How can lesions of the hippocampal formation present?
Single lesion capable of causing short-term memory loss but NOT long-term memory loss
The cingulate gyrus, parahippocampal gyrus and uncus are bumpy (i.e. have something underneath them). What is found underneath each structure?
- Cingulate gyrus; bundle of white matter association fibres underneath (cingulum)
- Uncus; collection of grey matter cell bodies (amygdala)
- Parahippocampal gyrus; hippocampus
What is the stria terminalis? What does it connect?
- 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
What does the fornix connect?
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Fornix; C-shaped tract that connects hippocampus to hypothalamus (including mamillary bodies)
- Explains why emotions can trigger autonomic responses (e.g. increased HR)
Why are the stria terminalis and fornix C-shaped?
Follow the curves of the lateral ventricles
Connections of the amygdala:
- 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
What does the hippocampal formation consist of?
Hippocampal formation refers to; dentate gyrus & hippocampus proper
What does the hippocampal formation form the floor of?
The inferior horn of the lateral ventricles
What structure contains the main efferent fibers of the hippocampus?
Fornix
How do axons leave the hippocampal formation?
- 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)
What is the hippocampal commissure?
allows for communication between fornices on each side
Planes of dissection
What is the Circuit of Papez? What structures does it involve?
- Closed, bidirectional circuit
- Involves;
- Hippocampus and adjacent cortex
- Fornix
- Mamillary bodies
- Anterior nucleus of thalamus
- Cingulum
Function of circuit of papez?
- Important in reinforcement of emotion, memory and olfaction with each other for survival responses
- Cortical control of emotion and memory storage
Explain the circuit of papez pathway
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
What are mamillothalamic fibres?
going from mamillary bodies to thalamus (anterior nucleus)
Which part of the thalamus is invovled in the circuit of papez?
Anterior nucleus of thalamus
What type of memory is the hippocampal formation involved in?
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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
Where does the hippocampus receive info via (i.e. input)?
Via the cingulum: from many areas including cingulate gyrus and other cortical areas
What is the major output tract of the hippocampus?
Fornix
The fornix connects the hippocampus to the mamillary bodies of the hypothalamus. Where do the fibres pass after this?
- 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
How is short term memory turned into long term memory?
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
Endocrine function of the hippocampal formation?
- Inputs to hypothalamus, modulatory role
- Hypothalamus connected to pituitary
What part of the brain is involved in short term memory?
Hippocampus
What part of the brain is involved in long term memory?
Neocortex
What is ‘working memory’? What part of the brain is involved in this?
- Limited capacity that can hold information temporarily, important for reasoning and guidance of decision-making and behaviour e.g. exams
- Hippocampus
What is the limbic system? What 4 functions is it involved in?
Group of grey and white matter structures lodged deep within the cerebrum. Involved in;
- Olfaction
- Emotional responses
- Behavioural activities
- Memory
What are the 2 main compenents of the limbic lobe?
- Cingulate gyrus (at top)
- Parahippocampal gyrus (at bottom, in temporal lobe)
What is the parahippocampal gyrus mainly involved in?
Memory
What 3 components makes up the hippocampal formation?
- Dentate gyrus (afferent component of hippocampal formation)
- Subiculum
- Hippocampus proper
1ary function of amygdala?
- Emotional responses (including response to smell)
- Behaviours
What are the 1ary grey matter components of the limbic system?
- Limbic lobe (cingulate gyrus & parahippocampal gyrus)
- Hippocampal formation
- Amygdala
- Thalamus
- Hypothalamus
- Septal area
- Habenula
What is the septum pellucidum?
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
What does the fornix connect?
Hippocampus –> Hypothalamus (mamillary bodies)
What is the major outflow tract of the amygdala? What does it connect?
Striae terminalis; amygdala –> septal area + hypothalamus
What is the septal area?
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.
Which tract/fibres connect the mamillary bodies to the anterior nucleus of the thalamus?
Mammillo-thalamic tract/fibres
Function of the anterior nucleus of the thalamus?
display functions pertaining to memory
What are the 2 directions that the circuit of Papez can take?
- Hippocampus –> fornix –> mamillary bodies –> mammillothalamic fibres/tract –> thalamus (anterior nucleus) –> cingulate gyrus/cingulum –> hippocampus (via dentate gyrus – this is the afferent component)
- Hippocampus –> fornix –> mamillary bodies –> mammillothalamic fibres/tract –> thalamus (anterior nucleus) –> cingulate gyrus/cingulum –> pre-frontal cortex
Via which tract do fibres pass from the mamillary bodies to the anterior nucleus of the thalamus?
Mamillothalamic fibres
Which nucleus of the thalamus is involved in the circuit of Papez?
Anterior nucleus
Function of the involvement of the prefrontal cortex in the circuit of Papez?
To involve memory in thoughts and decision making
