2 of 3

The Components of Basal Ganglia

The principal anatomical units of basal ganglia include:
Caudate nucleus,
Globus pallidus

The substantia nigra, and the subthalamic nucleus are generally included on a functional basis, while the amygdaloid body, located in temporal lobe, is functionallly excluded.

The major divisions of the basal ganglia are:
corpus striatum is constituted by neostriatum (caudate + putamen) and paleostriatum (globus pallidus)- concerned with primarily with somatic motor functions
amygdaloid nuclear complex, functionaly related to the hipothalamus and regarded as an integral part of the limbic system.

Corpus striatum

Constituted by:
Caudate nucleus (its head). Is an elonged C-shaped nuclear mass consisting of a head, body and tail. The caudate (cauda, tail) is separated from the thalamus and lentiform nucleus by the fiber mass of the internal capsule. The head of the caudate lies anterior to the thalamus and bulges into the lateral ventricle. The body in turn becomes further attenuated to form the tail which courses along the roof of the temporal horn of the ventricle and terminates at the amygdaloid nucleus.

Putamen is the largest part of the striatum, makes up the outer portion of the lenticular nucleus and is separated from the more laterally situated insular cortex. The putamen is continuous with the head of the caudate rostrally.
Situated between the insula, the caudate nucleus and the thalamus

Its neurotransmitters include:
Gamma-aminobutyric acid (GABA)

Tracts conveying impulses from the globus pallidus and striatum to the substantia nigra contain GABA, while tracts carrying impulses from the substantia nigra to the caudate and putamen store dopamine in their terminals. This represents the most important source of dopamine in the striatum. Failure of dopamine syntesis in the substantia nigra provokes a progressive depletion of this chemical substance in the caudate and putamen, with a consequent development of Parkinson's disease.

Lentiform nucleus
(or lenticular nucleus)

Constituted by:
Globus pallidus - The GP is situated medial to the putamen and is seperated from it by a thin lamina of myelinated fibers called the external medullary lamina.The globus pallidus appears pale and homogeneus because of its myelinated fibers.

The descriptive term "lenticular" or "lentiform" nucleus is applied to the putamen and globus pallidus togeather because of their combined lens-shape in brain sections.

The globus pallidus can be divided into two parts: the globus pallidus medial (GPm)and the globus pallidus lateral (GPl). Both receive input from the caudate and putamen, and both are in communication with the subthalamic nucleus. It is the GPm, however, that sends the major inhibitory output from the basal ganglia back to thalamus. The GPl also sends a few projections to the midbrain presumably to assist in postural control.

Substantia Nigra

Although a component of the brainstem, the substantia nigra is considered along with the basal ganglia because it has reciprocal connections with and is functionally related to the basal ganglia.

It can be divided into two parts: the substantia nigra pars compacta (SNpc) and the substantia nigra pars reticulata (SNpr). The SNpc receives input from the caudate and putamen, and sends information right back. The SNpr also receives input from the caudate and putamen, but sends it outside the basal ganglia to control head and eye movements. The SNpc is the more famous of the two, as it produces dopamine, which is critical for normal movement. The SNpc degenerates in Parkinson's disease, but the condition can be treated by giving oral dopamine precursors.

Claustrum Derived from a Latin word meaning a barrier. is a thin sheet of gray matter.
It is located medial to the insular cortex and overlying the lateral surface of the putamen.
It appears to have widespread reciprocal connections with sensory, particularly visual and somatosensory areas, of the cerebral cortex via association fasciculi in the extreme capsule. It also receives input from the hypothalamus (lateral), the thalamus (centromedian nucleus), and the locus ceruleus. Fibers from numerous cortical areas each terminate in distinct zones within the claustrum. Thus, it contains discrete somesthesic, visual and auditory zones. The claustrum has no subcortical projections.

Although there are many different neurotransmitters used within the basal ganglia (principally ACh, GABA, and dopamine), the overall effect on thalamus is inhibitory. The function of the basal ganglia is often described in terms of a "brake hypothesis". To sit still, you must put the brakes on all movements except those reflexes that maintain an upright posture. To move, you must apply a brake to some postural reflexes, and release the brake on voluntary movement. In such a complicated system, it is apparent that small disturbances can throw the whole system out of whack, often in unpredictable ways. The deficits tend to fall into one of two categories: the presence of extraneous unwanted movements or an absence or difficulty with intended movements.

Author: Dr. Silvia Helena Cardoso, PhD.

Center for Biomedical Informatics
State University of Campinas, Brazil

Copyright 1997 State University of Campinas