Basal Ganglia

Basal ganglia

The basal ganglia is a collection of interconnected subcortical nuclei (neuronal cell bodies) lying deep below the cortex. It is composed of the caudate nucleus, the putamen, the nucleus accumbens (or ventral striatum) and the globus pallidus.

Functionality

• Input nuclei:caudate nucleus (CN), the putamen (Put), and the accumbens nucleus (Acb) are all considered input nuclei.
• Cortical and thalamic efferent information enters the striatum (CN, Put, and Acb) to be processed further within the basal ganglia system
• Output nuclei: send basal ganglia information to the thalamus and consist of the internal segment of the globus pallidus (GPi) and the substantia nigra pars reticulata.
• Output nuclei project mainly to the thalamus (ventral nuclei), which, in turn, project back to the cerebral cortex (mainly frontal lobe)

Nuclei of the Basal Ganglia

• The putamen (laterally) and globus pallidus (medially) which together form the lenticular or lentiform nucleus (lens shaped). The caudate and putamen are also called the neostriatum or even referred to as caudate-putamen as a single entity. They communicate across the anterior limb of the internal capsule by fbrous strands that cross to connect these structures and so gives the area the name of the corpus striatum. Functionally the caudate and putamen are similar. The putamen is the larger ovoid mass which lies laterally with its lateral side separated very slightly from insular cortex and the external capsule and claustrum. Medially attached to the Globus Pallidus. The Globus Pallidus is smaller triangular shaped structure and lies medially with its medial relation being the internal capsule. The globus pallidus is a major source of output from the basal ganglia. It is divided by a lamina into Globus pallidus externa and interna.
• The caudate nucleus is a large mass of grey cells making up a head, body and tail. Anteriorly seen on scans at the lateral border of the anterior horn of the lateral ventricle. It lies then on the lateral wall of the ventricle and there is a tail which passes to form the roof of the inferior temporal horn of the ventricle. The internal capsule separates it from the putamen. The caudate is notable as being diminished in size in Huntington's chorea. The caudate and putamen receive stimulatory input from the cerebral cortex mediated (Glutamate) and from the substantia nigra (Dopamine). The caudate/putamen gives inhibitory output (GABA) to the Globus pallidus and substantia nigra. The Globus pallidus and Substantia nigra also send inhibitory signals to the ventral thalamic nucleus of the thalamus (GABA) which in turn feeds to the cortex (glutamate). The Basal ganglia is concerned with movements of the contralateral limbs and it would seem that it stimulates and inhibits various regions thus modulating motor output. All of these structures are prone to lacunar infarcts and deep haemorrhage
• Subthalamic nuclei are also part of the basal ganglia. Damage here can lead to dyskinesias and hemiballismus and associated motor disorders.