Limbic System | Anatomy2Medicine
Limbic System

Limbic System

 

  • Limbic System
  • is considered to be the anatomic substrate underlying behavioral and emotional expression.

 

      • plays a role in feeling, feeding, fighting, fleeing, and undertaking mating activity.

 

  • expresses itself through the hypothalamus via the autonomic nervous system (ANS).

 

    • Major components and connections
      • include structures of the telencephalon, diencephalon, and midbrain.

 

  • Orbitofrontal cortex

 

        • mediates the conscious perception of smell.

 

  • has reciprocal connections with the mediodorsal nucleus of the thalamus.
  • is interconnected via the medial forebrain bundle with the septal area and hypothalamic nuclei.
  • Mediodorsal nucleus of the thalamus
  • has reciprocal connections with the orbitofrontal and prefrontal cortices and the hypothalamus.

 

        • receives input from the amygdaloid nucleus.
        • plays a role in affective behavior and memory.

 

  • Anterior nucleus of the thalamus

 

        • receives input from the mamillary nucleus via the mamillothalamic tract and fornix.
        • projects to the cingulate gyrus.

 

  • is a major link in the limbic circuit of Papez.
  • Septal area

 

        • is a telencephalic structure.
        • has reciprocal connections with the hippocampal formation via the fornix.
        • has reciprocal connections with the hypothalamus via the medial forebrain bundle.
        • projects via the stria medullaris (thalami) to the habenular nucleus.

 

  • Limbic lobe
  • includes the subcallosal area, the paraterminal gyrus, the cingulate gyrus and isthmus, and the parahippocampal gyrus, which includes the uncus

 

        • contains the hippocampal formation and the amygdaloid nuclear complex.
        • Hippocampal formation
          • functions in learning, memory, and recognition of novelty
          • receives major input via the entorhinal cortex.
          • projects major output via the fornix.

 

  • Amygdaloid complex (amygdala)

 

          • produces activities associated with feeding and nutrition when stimulated.
          • may cause rage and aggressive behavior when stimulated.
          • Major afferent connections to the amygdaloid complex

 

  • Olfactory bulb and olfactory cortex

 

            • Cerebral cortex (limbic and sensory association cortices)

 

  • Hypothalamus

 

          • Major efferent connections from the amygdaloid complex
            • Cerebral cortex (limbic and sensory association cortices)

 

  • Hypothalamus
  • Brainstem and spinal cord
  • Hypothalamus

 

          • is a major part of the limbic system
          • projects to the brainstem and spinal cord

 

  • Limbic midbrain nuclei
  • Ventral tegmental area

 

            • projects ascending dopaminergic fibers to all limbic structures

 

  • Raphe nuclei of the midbrain

 

            • project ascending serotonergic fibers to all limbic structures

 

  • Locus ceruleus

 

            • projects ascending noradrenergic fibers to all limbic structures.
    • Papez circuit
      • is a circular pathway that interconnects the major limbic structures
      • contains the following stations:

 

  • Hippocampal formation

 

          • projects via the fornix to the mamillary nucleus.

 

  • Mamillary body

 

          • projects via the mamillothalamic tract to the anterior nucleus of the thalamus.

 

  • Anterior nucleus of the thalamus

 

          • projects to the cingulate gyrus.
          • receives the mamillothalamic tract.

 

  • Cingulate gyrus
  • projects via the entorhinal cortex to the hippocampal formation

 

    • Functional and clinical considerations

 

  • Hippocampus

 

        • has a low threshold for seizure activity.
        • is involved in learning and memory.

 

  • Bilateral ablation results in the inability to form long-term memories.
  • Cingulate gyrus

 

        • Lesions result in akinesia, mutism, apathy, and indifference to pain.

 

  • Amygdaloid nucleus

 

        • modulates hypothalamic and endocrine activities.
        • has the highest concentration of opiate receptors in the brain.
        • has a high concentration of estradiol receptors.

 

  • Bilateral lesions result in placidity, with loss of fear, rage, and aggression.
  • Klüver-Bucy syndrome
  • results from ablation of the temporal poles, including the amygdaloid nuclei, the hip- pocampal formations, and the anterior temporal neocortex.

 

        • may result from
          • temporal lobe surgery for epilepsy
          • viral encephalitis (e.g., herpes sim- plex virus affects primarily the temporal lobes), temporal lobe contusions due to head trauma.
        • is characterized by

 

  • placidity, hypersexuality
  • hyperphagia, and psychic blindness (visual agnosia).
  • Korsakoff syndrome (amnestic–confabulatory syndrome

 

      • Mamillary bodies and the mediodorsal nucleus of the thalamus are damaged

 

  • Seen in chronic alcoholism and thiamine (vitamin B1) deficiency

 

      • considered to be a late chronic stage of Wernicke encephalopathy
      • Clinical signs include

 

  • memory disturbances (amnesia)
  • confabulation
  • temporospatial disorientation.