Limbic System Anatomy Flashcards
What are the major limbic cortical areas of the limbic system?
Parahippocampus
Cingulate gyrus
Prefrontal cortex
Temporal pole
- other structures include*
- hippocampus
- amygdala
- septal area
Limbic system structures are the structures that directly or indirectly communicate with the hypothalamus and/or the PAG
What are the 4 main functions of the limbic system and the structures associated?
“HOME”
Homeostatic functions
- key structure = hypothalamus
Olfaction
- key structure = olfactory cortex
Memory
- key structure = hippocampal formation
Emotions and drives
- key structure = amygdala
Hippocampal formation
Contains 3 structures lumped together
Hippocampus
- contains CA1-4 fields of pyramidal cells
- CA1 aka = “sommers sector”
Dentate gyrus
- connects with CA3 pyramidal cells in hippocampus via mossy fibers and granular cells
Subiculum
- transitional region between hippocampus and entorhinal cortex
- regulates the HPA axis and endocrine functions assocaited with the hippocampal formation
What portion for the hippocampus is the most susceptible to hypoxia?
CA1 = sommers sector
- this is why when people, have epilepsy or seizures or clots/infarcts, memory issues tend to occur.
Afferent pathways in the hippocampal formation
2 pathways
Perforant pathways
- projects from the entorhinal region -> hippocampus
- CA1 -> CA2 -> CA3 -> CA4 -> entorhinal cortex
Alvear pathway
- projects from entorhinal cortex -> CA1/3
Efferent pathways of the hippocampal formation
Travels along the fornix to various structures
Precommissural fornix fibers -> septal area of the cerebrum
Post commissural fornix -> diencephalon
Commissual component -> contralateral hippocampus
* believed to be the reason why primary seizures on one hippocampus side can cause contralateral temporal damage/secondary seizures
What are the two primary thalamic nuclei associated with the hippocampus and limbic system
Medial dorsal and the anterior thalamic nuclei
Anterior = propagate head movements, alertness levels and learning/episodic memory formation
Medialdorsal = emotional responses to pain, movement of the eyes and learning/episodic memory formation
Functions of the hippocampal formation broadly
1) Spatial learning
- Short term memory and consolidation of memory to long term
- Receives and categorizes sensory information during learning
2) Modulates aggressive behavior
- activation of the portion closest to the AMYGDALA = Facilitates predatory attack behavior
- activation of the portion closest to the SEPTAL POLE = antagonizes this action
3) modulates endocrine functions
- specifically uses the ventral subiculum to regulate the hypothalamic-pituitary-adrenal axis via the medial corticohypothalamic tract
What are the parts of the parahippocampal gyrus?
Entorhinal cortex (anterior portion)
Parahippocampal cortex (posterior portion)
Perirhinal cortex (lateral portion)
- involved in the formation of new declarative memories (anterograde amnesia) and in spatial processing*
- damage leads to loss in the ability to form new memories and in ability to recognize scenes
- however, you can still recognize objects and shapes, just cant put it all together.
Papez circuit
Hippocampus -> fornix -> mammillary body -> mammillothalamic tract -> anterior thalamic nuclei -> thalamocingular tract -> cingulate gyrus -> cingulohippocampal fibers -> hippocampus
neuronal circuit used to establish connections between information stored in the unconscious and conscious behavior
Septal area function
Serves as the relay between hippocampal formation and the hypothalamus. Also is a feedback center for hypothalamus functions. Specifically
- aggression
- rage
- autonomic functions
- drinking/drug use
- suppression of ACTH and adrenal activity
- lesions here leads to Cushing’s syndrome as part of the sequela*
There are a medial and lateral septal areas and includes the bed of nucleus of atria and nucleus accumbens neuronal bodies.
Receives sensory afferents that modulate activity from
- medial olfactory stria
- hippocampal formation
- amygdala
- lateral hypothalamus (feedback only)
Sends efferent connections to the hypothalamus
- also can use nuclei of the diagonal band of Broca’s to widespread connections to other parts of the limbic system if need.
Function of the bed nucleus of the stria terminalis
Serves as the connection between the amygdala -> hypothalamus
Believed to regulate autonomic and endocrine processes
Function of the nucleus accumbens
Receives dopaminergic projections from the brainstem and other inputs from the amygdala and hippocampal formation
- projects to the substantia Nigra and innominate as well as the ventral tegmental area
Believed to integrate motor responses and associated them with specific afferent processes (usually extreme afferent process)
- i.e “unconsciously balling up your fist when very emotional”
Function of the substantia innominate
Contains the basal nucleus of Meynart
- projects to cerebral cortex and to other limbic systems as well as shares reciprocal connections with the amygdala.
Also believed to serve as the relay between amygdala -> lateral hypothalamus
is believed to play a part in Alzheimer’s disease when damaged
Nuclei of the amygdala
Contains 2 nuclei groups
Corticomeidal group
- cortical nuclei
- basal nucleus (medial part)
Basolateral group
- central nuceli
- lateral nuclei
- basal nucleus (lateral part)
