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Chapter: Human Neuroanatomy(Fundamental and Clinical): The Olfactory and Limbic Regions

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Connections of the Amygdaloid Nuclei

The amygdala receive fibres from, and send fibres to, the reticular formation, particularly theparabrachial nucleus.

CONNECTIONS OF THE AMYGDALOID NUCLEI

a.Connections with the brainstem

1.              The amygdala receive fibres from, and send fibres to, the reticular formation, particularly theparabrachial nucleus (Fig. 16.8).

2.              Noradrenergic fibres from the locus coeruleus, and serotoninergic fibres from the raphe nucleireach the amygdala through the medial forebrain bundle. Dopaminergic fibres ascend from the ventral tegmental area of the midbrain.


3.              Some fibres from the amygdala reach the nucleus of the solitary tract, and the dorsal nucleus ofthe vagus. The nucleus of the solitary tract projects back to the amygdala through the parabrachial nuclei. Through these connections the amygdala receive gustatory and visceral information can influence cardiovascular and respiratory functions.

b.Connections with the diencephalon

The amygdala send a major projection to various nuclei in the hypothalamus. Some fibres arealso received from the hypothalamus.

Fibres projecting to the thalamus end mainly in the medial dorsal nucleus. The impulses arerelayed to the prefrontal cortex. Afferents are received from the ventral posterior nucleus (gustatory sensations), and from the medial geniculate body.

c.Connections with the corpus striatum

        A prominent projection is sent to the striatum (caudate nucleus and putamen). Many fibres also reach the nucleus accumbens (which is a nucleus in the ventral striatum). Through the striatum the amygdaloid complex indirectly influences the pallidum, which in turn projects to the medial dorsal nucleus of the thalamus. The amygdaloid complex sends many fibres to the basal nucleus of Meynert (lying in the region ventral to the corpus striatum), This projection is cholinergic. The nucleus projects back to the amygdala.

d.Cortical connections of amygdala

       It is now known that in addition to its connections to olfactory areas, entorhinal area and hippocampus, the amygdaloid complex has numerous connections with widespread areas of neocortex. The areas include the cingulate gyrus, and parts of the frontal, temporal and occipital lobes, including the visual and auditory areas.

Clinical

      On the basis of all the connections described above, and on the basis of experimental studies it appears probable that the amygdala play an important role in the control of emotional behaviour. Lesions of the amygdaloid complex lead to the Kluver-Bucy syndrome. The experimental animals appear to be unable to correctly evaluate its environment leading to gross and bizarre alterations in eating behaviour, and in sex behaviour.


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