Basal Ganglia

The Parkinson's-Reversing Breakthrough

Parkinson Disease Handbook

Get Instant Access

The basal ganglia are a group of large nuclei located deep in the cerebral hemispheres. They are important because of their exclusively motor affiliation and because of the many disorders of movement that result from damage to these structures.

There is no uniformity of opinion about which structures should be included among the basal ganglia, but there is general agreement that the caudate nucleus, putamen, and globus pallidus should be listed under this heading. Many authors also include the midbrain substantia nigra and the subthalamic nucleus of the diencephalon as basal ganglia as well. In any case, the caudate, putamen, and globus pallidus are all generally situated at the base of the hemispheres, lateral to the thalamus and medial to the cerebral cortex (Fig. 11). The caudate is separated from the putamen and the globus pallidus by a thick band of white matter called the internal capsule, among the functions of which is the conveyance of motor impulses from the cortex to the motor neurons of the face and body below. Combinations of the basal ganglia also have frequently used names; hence, the caudate and putamen are known as the striatum, and the putamen and globus pallidus are referred to as the lenticular nucleus.

The principal function of the basal ganglia as an integrated unit is to modulate the activity of the motor cortex in the cerebrum as it organizes voluntary movement of the bodily musculature. Consistent with

Brain Template Printable

Figure 11 The positions of the basal ganglia and the substantia nigra within the hemispheres. Abbreviations: C, caudate; P, putamen; GP, globus pallidus; SN, substantia nigra. Reprinted with permission from Filley, C. M. (2001). Neurobehavioral Anatomy, 2nd ed., p. 181. University Press of Colorado, Boulder, CO.

Figure 11 The positions of the basal ganglia and the substantia nigra within the hemispheres. Abbreviations: C, caudate; P, putamen; GP, globus pallidus; SN, substantia nigra. Reprinted with permission from Filley, C. M. (2001). Neurobehavioral Anatomy, 2nd ed., p. 181. University Press of Colorado, Boulder, CO.

this role, the basal ganglia are connected with the cortex via a series of parallel loops that permit extensive involvement in cortical motor output. The primary such loop consists of the following: multiple cortical inputs reach the striatum by way of the internal capsule and another white matter tract called the external capsule; from there, connections proceed first to the globus pallidus and to then the ventral anterior and ventral lateral thalamic nuclei; the final link involves connections that return back to the motor cortex, again via the internal capsule. Thus, the basal ganglia join the cerebellum as regions strongly connected to the voluntary motor system by relays in specific thalamic nuclei. This anatomic linkage provides powerful modulatory input to the motor system, integrating two other brain areas into the organization of movement and emphasizing the general importance of motor action in human life. As reviewed previously, the cerebellum has a prominent role in coordination; the basal ganglia, in contrast, can be thought of as contributing to the initiation and timing of movements, although the exact contribution of these nuclei is still being clarified.

A final aspect of basal ganglia anatomy to be considered is its neurochemical input that arises from the substantia nigra of the midbrain (Fig. 11). Pigmented cells of the substantia nigra send axons rostrally, where they deliver the neurotransmitter dopamine to the striatum. Dopamine serves as an activator of the basal ganglia and the motor system as a whole, and its deficiency or absence results in dramatic alterations in motor function. Individuals with Parkinson's disease, characterized by a loss of dopami-nergic cells in the substantia nigra, display the classic clinical features of bradykinesia (slowness of movement), rigidity, and tremor. This is the most important movement disorder because of its high prevalence and because of the fact that the provision of dopamine or similar agents can significantly alleviate the clinical symptoms of the disease.

Was this article helpful?

0 0
Conquering Fear In The 21th Century

Conquering Fear In The 21th Century

The Ultimate Guide To Overcoming Fear And Getting Breakthroughs. Fear is without doubt among the strongest and most influential emotional responses we have, and it may act as both a protective and destructive force depending upon the situation.

Get My Free Ebook


Post a comment