Lecture 6: Amygdala, hippocampus and frontal cortex Flashcards
What is the function of the limbic system and hippocampal complex?
Most important circuits for Flight/Fright/Fight (Fear) responses, for modifying behaviour so that fear is not always the first response to a potentially harmful situation AND also for the ongoing formation of memories.
Many drugs also act within this system
What is the clinical importance of the hippocampal and limbic system?
Change in its structure can lead to depression and anxiety, loss of sense of smell in neurodegenerative disease, memory loss, personality change in alzhiemers disease
What are the primary neurotransmitter pathways in the limbic and hippocampal systems?
Dopamine
Serotonin
Norepinephrine
What connects the lateral amygdaloid complex and the (medial) septal nucleus?
Stria terminalis, making these structures one in the same
What is the medial septal nucleas a part of and what does it recieve input from?
It is a part of the striatum and recieves input from the substantia niagra
What is the medial septal nucleus synonymous with?
Nucleus accumbens
Describe the limbic system?
- Olfactory bulb input
- Bifurcates into medial septal nucleus and lateral amygdaloid complex
- These are connected by the stria terminalis
- Medial septal nucleus recieves input from the substantia niagra via the medial forebrain bundle (striatal niagral pathway)
- No output
Describe the hippocampal complex:
- No DIRECT inputs, just many inputs
- Parahippocampal gyrus sits around the hippocampus (Clinically important)
- Hippocampus proper is made up of the dentate gyrus (Many small tooth like structures sitting in the wall of lateral ventricle) and fornix which follows the ventricle which divides into the pre and post commisural arm as it goes around the ant. commisure.
- Pre commisural arm goes to medial septal nucleus
- Post commisural arm goes to the mammillary body (important in memory) (highly sensitive to a lost of nutrition i.e alcoholics)
- Mamillary body sends fibres up through the mamillothalamic tract to the anterior thalamic nucleus
- No apparent output
What is the papezs circuit.? (Memory circuit, put down and recall)
Puts the hippocampal circuit and the amygdala complex together and from the Anterior thalamic nucleus projects to the cingulate gyrus
Parahippocampal gyrus -> Hippocampus -> Fornix Mamillary Body -> Anterior thalamic nucleus -> Cingulate gyrus Frontal cortex
NB: Papezs circuit is biggest contribhutor to memory. But not only source. It is also bidrectional
What inputs does the parahippocampal gyrus recieve that makes it form long term memory?
- All of the senses including those about smell
How does the limbic and hippocampal systems interact?
Pre-commisural arm of the fornix connects to medial septal nucleus and the hypothalamus connects the MSN and the mamillary body.
Describe the dopamine circuit:
Dopamine fibres originate from the Substantia Niagra and project to the striatum-GPi (basal ganglia) and to the medial septal nucleus (nucleus accumbens) which is involved in reawrd based decision making. This projects onto the cingulate gyrus
So when parkinsons is treated with L-dopa it can also act on the n. accumbens and increase risky behaviour. This can lead onto depression and potentially psychosis if too much dopamine is around.
