The globe pallidus is a small mass of gray matter that is located at the base of the brain. It turns out the smallest nucleus of the basal ganglia. It connects directly with the putamen and the caudate nucleus, and its projections are directed towards the thalamic nuclei. Its union with the putamen forms the lenticular nucleus.
Its main functions are related to the control of voluntary sub-conscious movements, such as the coordination of gait or the movement of the arms. Likewise, alterations in this region of the brain are often associated with Parkinson's disease.
Pale balloon (light blue)
The globe pallidus is a subcortical structure of the brain. It constitutes a region of the telencephalon, so they are located in the uppermost areas of the brain.
Characteristics of the pale globe
Despite being part of the telencephalon, the globe pallidus stands out for containing multiple connections with the subcortical regions of the brain, especially with the thalamus and subthalamus.
In fact, together with the thalamic nuclei, the globe pallidus constitutes the motor circuit known as the extrapyramidal system.
On the other hand, the globe pallidus stands out for being part of the basal ganglia. In this sense, it is a structure that establishes connections with the other components of the basal ganglia, such as the putamen, the nucleus accumbens and the caudate nucleus.
Finally, the specific connection between the globus pallidus and the putamen make up another system known as the lenticular nucleus.
Anatomy
Pale balloon (red).
The globe pallidus is made up of cells called pale neurons. These are characterized by presenting a large size with a high number of dendrites with extensions longer than most neurons.
Likewise, the dendrites of pale neurons have the peculiarity of having a three-dimensional shape of flat discs, parallel to each other. Dendrites are located on the border of the nucleus of the neuron and perpendicular to the afferent axons of the cell.
On the other hand, the globe pallidus is crossed by a large number of myelinated axons. The myelin contained in the axons of the neurons of this structure provide a white appearance to the nucleus, which is why it is called pale.
Finally, another peculiarity of the globe pallidus is that, due to the high length of its dendrites, these are found in all regions of the structure and constantly synapse.
Parts
In primates, the globe pallidum is divided into two large parts separated by the medullary lamina. The two structures that make up the globus pallidus are often called the inner and outer parts. Both regions are composed of closed nuclei, which are surrounded by myelinated walls.
Recently, a new way of naming the parts of the globe that distinguishes the nucleus between ventral pale and medial pale has been postulated.
The medial globe pallidus, as its name suggests, represents the middle region of the globe pallidus. It is smaller than the ventral part.
For its part, the ventral pallidum is found within the innominate substance and receives efferent connections from the ventral striatum. This part of the globe pallidus is responsible for projecting myelinated fibers to the dorsal and dorso-medial nuclei of the thalamus.
Likewise, certain neurons can be sent to the pedunculopontine nucleus and motor tegmental areas.
The activity of the ventral globus pallidus is much more important than that of the medial globus pallidus as it is responsible for projecting the fibers. In this sense, its main function is based on serving as a limbic-somatic motor interface. Likewise, it is involved in planning and inhibiting movements.
Function
The globe pallidus is a brain structure that is mainly involved in the regulation of voluntary movement. It constitutes a small part of the basal ganglia which, among many other things, regulate the movements that occur at the subconscious level.
When the pale globe is damaged, the person can experience movement disorders, since the system that controls these types of activities is dysregulated.
In cases where damage to the globus pallus is intentionally induced through a procedure called polydotomy, inhibiting this brain structure may be helpful in reducing involuntary muscle tremors.
This fact is explained because within the motor process of the brain, the globe pallidus plays a mainly inhibitory role. This inhibitory action serves to balance the excitatory activity of the cerebellum.
Thus, the function of the globus pallus and the cerebellum is designed to work in harmony with each other, thus producing adapted, controlled and uniform movements.
Cerebellum
Imbalances in either region can cause tremors, jerks, and other motor problems such as those seen in patients with degenerative neurological disorders.
It should be noted that, unlike other nuclei of the basal ganglia, the globe pallidus acts only at the unconscious level, so it does not participate in the execution of conscious movements such as, for example, eating, dressing or writing.
Related diseases
Diseases associated with dysfunctions or deterioration of the globe pallus are mainly motor conditions. In this sense, Parkinson's disease is the disorder that has been most significantly correlated with this brain structure.
This pathology causes a wide range of symptoms, among which motor manifestations such as tremors, stiffness in the arms, legs and trunk, slowness of movements, problems with balance and coordination or difficulties in chewing, swallowing or speaking stand out.
Of all these manifestations, it is postulated that dysfunction of the globe pallus would only explain the involuntary motor symptoms. That is, the stiffness of the muscles, loss of balance or tremors would be motivated by a condition in the globus pallidus-cerebellum functional complex.
In contrast, other symptoms such as slow movement or cognitive and psychological manifestations, would be associated with dysfunction of other brain regions.
References
- Yelnik, J., Percheron, G., and François, C. (1984) A Golgi analysis of the primate globus pallidus. II- Quantitative morphology and spatial orientation of dendritic arborizations. J. Comp. Neurol. 227: 200-213.
- Percheron, G., Yelnik, J. and François. C. (1984) A Golgi analysis of the primate globus pallidus. III-Spatial organization of the striato-pallidal complex. J. Comp. Neurol. 227: 214-227.
- Fox, CA, Andrade, AN Du Qui, IJ, Rafols, JA (1974) The primate globus pallidus. A Golgi and electron microscopic study. J. Hirnforsch. 15: 75-93.
- Di Figlia, M., Pasik, P., Pasik, T. (1982) A Golgi and ultrastructural study of the monkey globus pallidus. J. Comp. Neurol. 212: 53-75.