Limbic System Anatomy Flashcards

1
Q

What are the major limbic cortical areas of the limbic system?

A

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

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2
Q

What are the 4 main functions of the limbic system and the structures associated?

A

“HOME”

Homeostatic functions
- key structure = hypothalamus

Olfaction
- key structure = olfactory cortex

Memory
- key structure = hippocampal formation

Emotions and drives
- key structure = amygdala

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3
Q

Hippocampal formation

A

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
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4
Q

What portion for the hippocampus is the most susceptible to hypoxia?

A

CA1 = sommers sector

- this is why when people, have epilepsy or seizures or clots/infarcts, memory issues tend to occur.

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5
Q

Afferent pathways in the hippocampal formation

A

2 pathways

Perforant pathways

  • projects from the entorhinal region -> hippocampus
  • CA1 -> CA2 -> CA3 -> CA4 -> entorhinal cortex

Alvear pathway
- projects from entorhinal cortex -> CA1/3

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6
Q

Efferent pathways of the hippocampal formation

A

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

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7
Q

What are the two primary thalamic nuclei associated with the hippocampus and limbic system

A

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

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8
Q

Functions of the hippocampal formation broadly

A

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

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9
Q

What are the parts of the parahippocampal gyrus?

A

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.
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10
Q

Papez circuit

A

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

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11
Q

Septal area function

A

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.

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12
Q

Function of the bed nucleus of the stria terminalis

A

Serves as the connection between the amygdala -> hypothalamus

Believed to regulate autonomic and endocrine processes

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13
Q

Function of the nucleus accumbens

A

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”

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14
Q

Function of the substantia innominate

A

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

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15
Q

Nuclei of the amygdala

A

Contains 2 nuclei groups

Corticomeidal group

  • cortical nuclei
  • basal nucleus (medial part)

Basolateral group

  • central nuceli
  • lateral nuclei
  • basal nucleus (lateral part)
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16
Q

Amygdala lesions cause what

A

Kluver-Bucy syndrome

  • hypersexuality
  • excessive eating
  • decreases anxiety/fear
  • hyperorality
  • visual agnosia (can see but cant recognize what your seeing)
  • hypermetamorphosis (desire to touch everything you see)
17
Q

Amygdala connections

A

Afferent inputs

  • olfactory and taste nuceli
  • temporal neocortex
  • prefrontal cortex
  • ventromedial hypothalamus
  • substantia innominate
  • nuceli of the diagonal band of Broca’s
  • medial thalamus

Efferent outputs

  • to hypothalamus via stria terminalis
  • to PAG via stria terminalis
  • to prefrontal cortex via ventral amgyfugal pathway
18
Q

Functions of the amygdala

A

Mediates conditioned fear responses to auditory and visual stimuli
- both corticomedial and basolateral nuclei contribute equally.

aggressive behavior

  • stimulation of the corticomedial nuclei = increased rage
  • stimulation of the basolateral nuclei = decreased rage

feeding and drinking behavior

  • stimulation of the corticomedial nuclei = decreases drinking and hunger
  • stimulation of the basolateral nuclei = increases drinking and hunger
Induces ovulation (corticomedial nuceli stimulation only) 
* transaction of the stria terminalis removes this completely*

Endocrine functions

  • stimulation of corticomedial nuclei = inhibits ACTH and GH inhibts
  • stimulation of the basolateral nuclei = increases ACTH and GH release
19
Q

Limbic connections to basal nuclei

A

Caudate nucleus and ventral striatum fibers project to:

  • internal segment of globus pallidus
  • substantia Nigra pars reticulata
  • ventral tegmental area
  • lateral preoptic area
  • caudal mesencephalon

*All of the above then project to the mediodosal and ventral anterior thalamic nuclei *

20
Q

What psychiatric disorder is well connected to abnormalities in basal nuclei, anterior cingulate gyrus and serotonin function?

A

Obsessive-compulsive disorder
- abnormally increased activity in the basal nuclei especially in the head of the caudate and the anterior cingulate gyrus.

21
Q

What psychiatric disorder is well connected to abnormalities throughout the limbic system, frontal lobe and basal nuceli and dopamine production?

A

Schizophrenia

- decreases in volume of the amygdala, HF and parahippocampal gyrus

22
Q

What psychiatric disorder is well connected to abnormalities in the cerebral cortex, hippocampus and both BDNF and VEGF production?

A

Depression

  • global decrease in activity of the cerebral cortex, especially the frontal lobes.
  • decreased hippocampal volume, especially left hippocampus