Limbic System Flashcards
Functionally what is the limbic system?
The parts of the CNS that control:
- emotional components of our personalities
- form declarative memories (explicit)
- Survival functions like food/h20 intake, arousal, sex
Why is the limbic system called the limbic system?
Because limbic means rim, and the original structures of the limbic system were the rim of cerebral cortex surrounding the Diencephalon structures
What are the major cortical components of the limbic system?
- Classic limbic lobe (cingulate, isthmus, parahippocampal gyrus, subcallosal area)
- Hippocampus and subiculum
- Prefrontal cortex (medial, orbital, anterior cingulate)
What are the subcortical components of the limbic system?
- Amygdala
- Septal area
- Ventral basal ganglia (nucleus accumbens)
- Thalamus (dorsomedial and anterior nuclei)
- Hypothalamus (mammillary bodies and lateral area)
What are the major pathways between components of the limbic system?
- Perforant pathway
- Fornix
- Stria terminals
- Ventral amygdalofugal pathway
- Median forebrain bundle
What does the isthmus in the limbic system connect?
The cingulate gyrus to the parahippocampal gyrus
Anteriorly what does the cingulate gyrus curve under?
What is the underneath area called?
It curves under the genu of the corpus callosum and the area it connects to is the subcallosal cortex
What is the subcallosal cortex adjacent to?
The piriform cortex and olfactory tubercle
What does the piriform cortex merge with posteriorly?
The uncus and the rest of the parahippocampal gyrus
What is the major role of the hippocampus?
Formation of declarative memory through the papez circuit
What is the cortical structure of the hippocampus?
What kind of neurons are in the hippocampus?
It is a primitive structure so it has only 3 or 4 layers (like the closely related dentate gyrus)
The hippocampus is made of pyramidal cells arranged in a C formation intertwined with the dentate gyrus
What are the four pyramidal cell zones in the hippocampus?
Which type is especially susceptible to ischemia and is devastated in Alzheimer’s disease?
CA1-CA4 from closest to furthest from the subicular cortex
CA1
The hippocampus is an unfolding of what?
The medial temporal lobe
Where does the hippocampus receive input from?
Via what pathway?
The entorhinal cortex (part of the parahippocampal gyrus) via the perforant pathway
Where does most of the output from the hippocampus go?
- Diencephalon (mammillary bodies and ant. Thalamic)
- Septal area via the fornix
- Amygdala
What is the subicular cortex? What cells originate here?
An area right next to the hippocampus that gives rise to the axons of the fornix.
What two areas give rise to axons of the fornix?
- Subicular area
2. Ca1 cells in the hippocampus
What efferent of the hippocampus travels via the postcommisural fornix?
Diencephalon (mammillary bodies, anterior thalamic nucleus)
What efferents from the hippocampus travel via the precommisural fornix?
Septal areas
What is the role of the prefrontal cortex?
Behavioral planning
Social interaction
Working memory
Affect and mood
What are the three major areas of the prefrontal cortex?
- Orbital
- Medial (including anterior cingulate)
- Lateral
What is damage to the prefrontal cortex associated with?
Personality change
What does the prefrontal cortex receive input from?
- Dorsomedial nucleus of the thalamus
- Ventral basal ganglia
- Amygdala
- Olfactory
Where does the Amygdala lie?
Anterior temporal lobe in front of and superior to the hippocampus
What are the afferents to the Amygdala?
What is the pathway?
- Visceral,somatosensory, and special sensory
- Hippocampus
- Limbic areas
Pathway: stria terminalis or ventral amygdalofugal pathway
What is the main role of the Amygdala?
Emotional response to sensory input
What are the two pathways information leaves the Amygdala?
- Stria terminalis
2. Ventral amygdalofugal pathway
How does the stria terminalis travel?
What two structures does it travel between?
Where do the fibers go?
It forms a c loop around the hypothalamus parallel to the fornix.
It travels between the caudate nucleus and the thalamus.
Fibers go to septal areas and the hypothalamus
Whre does the ventral amygdalofugal pathway travel?
What five structures does it make connections with?
It is loose collection of axons that travels across the basal forebrain from the Amygdala to:
- Septal area
- Hypothalamus
- Limbic nuclei of the thalamus (dorsomedial and anterior)
- Ventral basal ganglia
- Neocortical limbic area
Where is the septal area located?
Below the septum pellucidum by the anterior commissure
What is the role of the septal area?
Emotions and with the nucleus accumbens, reward seeking behavior
What are the most prominent inputs to the septal area?
- Amygdala via stria terminalis and ventral amygdalofugal pathway
- Hippocampus via fornix
What part of the limbic system MOST directly influences the hypothalamic and brainstem areas involved in visceral responses?
The septal area
How does output from the septal area travel to the hypothalamus?
How does output get to that brainstem? What part of the brainstem?
Via the medial forebrain bundle
Via the brainstem tegmentum to the reticular formation
What areas of the basal ganglia are involved in limbic activity?
Ventral striatum and ventral pallidum
Where does the ventral striatum receive input from? Via what tract?
- The Amygdala via the ventral amygdalofugal pathway
- Prefrontal cortex (orbital and medial)
- Ventral tegmental area
What is the ventral tegmental area?
What neurotransmitter is it rich in?
What does it project to?
A dopamine rich cell population in the midbrain that is just medial to the pars compacta.
The ventral tegmental area projects to the ventral striatum
Where does output from the ventral striatum go?
To the Vental pallidum which goes to the dorsomedial nucleus of the thalamus and eventually to the prefrontal medial and orbital cortexb
What two areas are involved in reward seeking behavior and addiction?
Ventral striatum (nucleus accumbens) Septal area
What is the limbic basal ganglia loop?
Cortical input from the hippocampus, prefrontal orbital and medial cortex, Amygdala, ant cingulate excite the ventral striatum
The ventral striatum inhibits the ventral pallidum
The ventral pallidum inhibits the dorsomedial nucleus of the thalamus
The dorsomedial nucleus of the thalamus excites cortical areas
What two nuclei of the thalamus play the biggest role in limbic system function?
Anterior thalamic nucleus
Dorsomedial nucleus
What is the input and output to the anterior thalamic nucleus?
Input: mammillary bodies and hippocampus
Output: anterior cingulate gyrus
What is the major input and output to the dorsomedial thalamic nucleus?
Input: Vental pallidum, Amygdala, prefrontal cortex
Output: prefrontal cortex
What parts of the hypothalamus are most important for limbic function?
- Mammillary bodies- memory
- PVH- anterior pituitary influence
- Dorsomedial and Ventromedial - emotion, survival, reproduction
From what limbic areas does the hippocampus receive input?
Hippocampus via the fornix
Amygdala via the ventral amygdalofugal
Septal area and brainstem tegmentum via median forebrain bundle
What are the two major functional divisions of the limbic system?
- Explicit (declarative) memory
2. Behavior and emotion
The formation of declarative memory centers around what limbic structure?
Hippocampus
Emotion and behavior focus around what limbic structure?
The Amygdala
Input to the hippocampus is via what pathway and structure?
Onto What structure in the hippocampus do these axons synapse?
The entorhinal cortex via the perforant pathway
They synapse on the dentate gyrus of the hippocampus
From the dentate gyrus, where does the circuit travel?
Dentate gyrus via mossy fibers to ca3
Ca3 via Schaffer collaterals to ca1
Ca1 and subicular neurons to fornix
After the fornix leaves the hippocampus, it branches into two divisions. What are they and where do they go?
Pre commissural to the septal areas
Post commissural to the mammillary bodies and anterior thalamic nuclei
Where do projections from the mammillary bodies go when regulating the formation of memory?
Through the mamilla thalamic tract to the anterior thalamic nuclei
Where do projections from the anterior thalamic nuclei go when forming memory?
To the anterior cingulate gyrus which loop back through the parahippocampal gyrus to the entorhinal cortex which projects back onto the hippocampus
What does the papez circuit do?
What is the path?
Forms short term retention of explicit memory
Entorhinal cortex to dentate gyrus to mossy fiber to ca3 to Schaffer collateral to ca1 to subiculum to fornix to post commissural path to mammillary bodies to anterior thalamic nucleus to cingulate gyrus to parahippocampal gyrus to entorhinal cortex
Bilateral injury to the dorsomedial nucleus of the thalamus result in what?
Memory deficits similar to a bilateral hippocampal deficit
What are the three major steps in forming a response to emotional stimuli?
- Receive the triggering stimuli or memory (Amygdala )
- Form an emotional response:
- visceral motor (HR, dilated pupil, sweating)
- somatic motor response (grimace, smile, fists) - Conscious awareness of the stimulus to react to it
When forming an emotional response or memory, what are the inputs to the Amygdala? What are the outputs?
Inputs: hippocampus and visceral, somatosensory, special sensory
Output : septal areas and hypothalamus to control visceral response, limbic basal ganglia loop to form cognitive response
