Limbic System Flashcards
The limbic system referred to the curved rim of cortical tissue that borders the cerebral hilum (limbic means bordering or edge). Functionally, this definition also includes the subcortical nuclei associated with these cortices, and have special functions, and the axonal fiber tracts that link various nuclei and cortices. Currently, what does the limbic system refer to?
The limbic system is a collection of cortical and subcortical brain components that are structurally interconnected, and functionally integrated, with each other, and with other parts of the nervous system; that are concerned with self perpuation and self propagation. These are a variety of diverse functions from behavior and emotions to memory.
OR
The entire neuronal circuitry that controls emotional behaviour and motivational drives.
State the key characteristics of the limbic system.
- Presence of allocortices (archicortex and paleocortex) on some structures. [Allocortices do not have the 6 histological layers unlike the neocortex. Archicortex has 3-4 layers, paleocortex has 3 layers. The mesocortex (cortex of the cingulate gyrus) is a transitional cortex.]
- Neurons display prolonged afterdischarge within some circuits (this could explain why there’s long term memory or why some emotional experiences are felt for so long).
- Although present, there is paucity of neocortical input.
State the functions of the limbic system.
- It contributes to the processes of learning and memory: important in processing new information, causing reinforcement or habituation (ignoring the info).
- Emotional control: creates emotional responses (fear, rage and placidity), as well as visceromotor (endocrine and autonomic) responses to certain sensory inputs (e.g. blood pressure rising due to fear).
- Addiction and motivation: has reward circuitry that causes excitations and cue-induced relapses that lead to addictive behaviours.
- Sexual behaviour: receives genitosensory signals and provides responses that are consistent with sexual excitement/it facilitates behaviours integral to sexual reproduction
- Food intake: control appetite and eating behaviours e.g. food choice and satiety.
- Social cognition: help develop thought processes involved in understanding and dealing with other people.
- Sleep and dreams: interweaves unconscious emotions with conscious cognitive thoughts and perceptions, linking emotions and memory during sleep.
- Vegetative functions: responses influence temperature, osmolality, appetite e.t.c.
- Olfaction: processing of olfactory sensation, emotional response to smell and creating olfactory memory
Here’s something easier to remember: The 5 Fs Mnemonic
Key functions of the limbic system:
1. Feeding (satiety and hunger)
2. Forgetting (memory)
3. Fighting (emotional response)
4. Family (sexual reproduction and maternal instincts/social cognition)
5. Fornication (sexual arousal)
The limbic system has subcortical nuclei associated with the limbic lobe, the limbic lobe itself and fiber tracts connecting the various nuclei and cortices. List the cortical and subcortical structures making up the limbic system.
Cortical structures:
- limbic lobe
- hippocampal formation
- septal area
- olfactory areas
Subcortical structures:
- amygdaloid nuclear complex
- reticular formation
- hypothalamus
- anterior and medial nuclei of thalamus
- habenular nucleus
List the components of the limbic lobe (4).
What are the parts of the hippocampal formation (these are some structures within the mesial/medial temporal lobe)? (7)
The limbic cortex largely functions as a transitional zone through which signals are transmitted from the neocortex. TRUE or FALSE?
TRUE
What is the role of the orbitofrontal cortex?
- actively involved in the cognitive process of decision making
- important in processing reward behaviours
State the function of the subcallosal (paraolfactory) area/Zuckerkandl’s gyrus (note that this is different from the subcallosal gyrus/paraterminal gyrus).
Involved in development of negative mood, and regulation of some autonomic responses.
What is worth noting about cingulate gyrus? (Afferents and efferents, role, implicated in disorders like)
- receives inputs from neocortex, and projects the signals to the hippocampal formation
- has a role in emotion formation and processing, learning and memory, autonomic functions and pain processing
- implicated in disorders such as depression and schizophrenia
State the role of the parahippocampal gyrus.
- provides a major path by which sensations converge on the hippocampus
- involved in encoding and recognising social and environmental scenes
State the functions of the insular cortex.
- processes convergent information to produce a subjective emotion that is relevant for the context
- taste, hearing, autonomic and salience
Click on Answer to view images of the hippocampal formation. Try to identify all the features of the hippocampal formation.
The parahippocampal gyrus is the entorhinal area, Brodmann Area number _____. Which functional cortex was that?
- Primary olfactory cortex
State the connections of the hippocampus.
Afferent: Hippocampus receives fibres mainly from entorhinal area (area 28), olfactory cortex, amygdala, opposite hippocampus, parahippocampal gyrus.
Efferent: The fornix is the main efferent tract of the hippocampus. The fibres leaving the hippocampus pass:
*To the opposite hippocampus through the commissure of fornix/hippocampal commissure
* To the septal and anterior hypothalamic regions
* To the mamillary body, which sends impulses to cingulate gyrus through anterior nucleus of thalamus, through Papez circuit
