The globus pallidus, also called the pallidum, is located in the central area of the brain, where it is responsible for activating all movement processes of the human body. From this function, it is assigned to the basal ganglia (basal nuclei), which belong to the cerebrum and are located below the cerebral cortex.
What is the globus pallidus?
Developmentally, the pallidum is a part of the diencephalon. Its German name, translated from Latin, is “pale globe.” This name refers to the microscopically nearly colorless appearance of the globus pallidus, which is composed of many large and conspicuously pigment-poor neurons. It is surrounded in the brain by the putamen, the so-called shell body, and separated from it by a lamella of white matter. The white matter is composed of interconnected nerve fibers that conduct information streams through the various brain areas. This lamina is the lamina medullaris lateralis (externa). In addition, the lamina medullaris medialis (interna) separates the pallidum into a lateral or outer portion (globus pallidus lateralis) and a medial or inner portion (globus pallidus medialis). These two areas of the “pale globe” each fulfill different tasks. These can be described as promoting movement (pars externa) and inhibiting movement (pars interna). Here, however, in accordance with the function of the pallidum, the movement-promoting part predominates, which is finally translated into concrete physical activities. Thus, the globus pallidus acts as a link to the striatum (striate body) as well as the thalamus (diencephalon), from which the movement impulses originate. Along with the putamen and pallidum, the caudate nucleus (caudatus) is one of the core areas of the basal ganglia. They give rise to the regulation of the entire motor system in humans. The pallidum lies furthest inward in the entire area of the basal ganglia. Attached to it in a disc-like fashion is the putamen, which in turn is embraced by the caudate like a tail. Hence the name tail nucleus for the caudate nucleus. The individual nuclei of the basal ganglia are delimited by fiber bodies mutually as well as in relation to the diencephalon. These fibrous masses are also medically called internal capsule (capsula interna). This capsule also extends between the caudate and putamen in the form of very narrow stripes, which is why the striatum is nicknamed the striate body.
Anatomy and structure
The globus pallidus receives the movement-inhibiting impulses from the striatum, and the movement-promoting impulses from the thalamus. The stronger movement-promoting commands, in turn, originate toward the thalamus. This explains the predominantly active effect on the locomotor system of the organism. At the same time, the basal nuclei as a whole act as a filter system that allows desired and possible movements at any given moment, while preventing undesired or just not possible movements. The fine balance between inhibiting and stimulating a movement is the speciality of the globus pallidus. Together, these two properties highlight the exceedingly complicated feedback process that occurs many thousands of times every minute as part of a person’s motor activities.
Function and tasks
This feedback is positive in nature and is called a neural loop. To prevent it from leading to excessive excitation of the motor system, constant “dampers” in the form of the impulses that inhibit movement are necessary. This damping is provided by the outer pallidal limb with the so-called nucleus subthalamicus (Luys body). This nucleus in the diencephalon sends excitatory signals toward the inner pallium member, where they are converted into inhibitory synapses. This negative feedback loop slows down the activity of the entire motor system and causes it not to spiral out of control. If such a “feedback catastrophe” were to occur, for example by destroying the nucleus subthalamicus, affected persons would have to experience an overshooting of uncontrollable, atypical and seizure-like movements of the extremities. These effects are called “ballisms,” derived from the Greek word “ballein” (to throw). They may manifest themselves in a person suddenly moving erratically in public as if he or she were trying to kick loud footballs or throw handballs. A person affected in this way has possible dangers for other people out of sight, and he cannot prevent these movements in the least by himself.
Diseases
The basal ganglia, with the pallidum as their fulcrum, not only control the entire so-called voluntary motor system, but are involved in the complete system of all externally noticeable human performance. Thus they have significance for fields of action such as drive, initiative, planning, participation, spontaneity and willpower. If the complicated communication paths within the basal nuclei are disturbed, premature degeneration (aging) of affected nerve cells can be the result. These processes can lead, for example, to the symptoms of Parkinson’s disease. Other possible neurological disorders in this regard include multisystem atrophy (MSA), several dystonia syndromes, Huntington’s disease, ADHD, and Tourette’s syndrome. Specifically, in Parkinson’s disease, these degenerations cause loss of movement (hypokinesia), postural instability, changes in muscle tone, decreased sense of smell, and tremor (tremor). The preceding damage to the basal ganglia can trigger such symptoms already in the early childhood developmental stage, for example, after brain damage as a result of oxygen deficiency. The deposition of copper in the basal nuclei may cause Wilson’s disease, a disorder that causes complex motor and also mental defects. Recurrent compulsive actions can also be explained by deficiencies in the globus pallidus area. Thus, the so-called tic disorders are characterized by the fact that, due to faulty switching of the basal ganglia, an irregular sequence of movements occurs again and again, which becomes firmly established in the daily behavior of the diseased person and can later no longer be avoided.
