Globus pallidus: structure, functions, and associated disorders

Although they are not as well known to most people as brain lobes, the subcortical regions of the brain they serve equally important functions. Specifically, the areas that we know as basal ganglia are essential for movement, among other aspects.

One of the nuclei that make up the basal ganglia is the globe pallidus, the smallest of all. We'll see now the structure and functions of the globe pallidus, as well as the disorders that are related to lesions in this region, among which the disease of Parkinson's.

What is the pale globe?

The pale globe is also known as paleo-striatum. It is a subcortical structure composed of gray matter (i.e., neuron cell bodies, dendrites without myelin, and glial cells) that develop from the diencephalon, although it is part of the telencephalon. Therefore, it is located in the anterior part of the brain, on the inner side of the frontal lobe.

It is part of the extrapyramidal system, a neural network that controls and regulates involuntary movements. The extrapyramidal tracts send projections primarily to the lower motor neurons of the spinal cord that are concerned with movement, reflexes, and posture.

This structure is more developed in primates than in other animals; in particular, the inner region of the globe pallidus is only found in humans and our closest relatives.

• Related article: "Basal ganglia: anatomy and functions"

The basal ganglia

The pallidus is one of the structures that make up the basal ganglia, a set of closely related subcortical nuclei that are located around the third ventricle. The basal ganglia fulfill functions mainly related to voluntary and automatic movements.

The nuclei that form the basal ganglia, in addition to the pale globe, are the following:

• Striated body: receives information from the other basal ganglia, integrates it and sends it to higher areas of the brain.
• Caudate nucleus: has connections with the frontal lobe and is involved in motivation and alarm response.
• Black substance: relevant for the control of fine motor skills; It is part of the brain's reward system because it has many dopaminergic synapses.
• Nucleus accumbens: Like the black substance, it is part of the reinforcement system, so it has a key role in the development of addictions.
• Putamen: this structure intervenes in automated movements, especially those of the face and extremities.
• Subthalamic nucleus: connects the midbrain and thalamus and regulates motor skills.
• Red substance: This region is important for coordination in general and that of the upper extremities in particular.

Structure and anatomy

The globe pallidus is mainly composed of very large neurons with a large number of dendritic branches. The pale globe appearance is peculiar because of the abundance of dendrites and their unusual length.

The name of this structure is due to the fact that it is crossed by many myelinated axons that connect other regions of the ganglia basal with the pale globe, giving it the characteristic whitish tone of cerebral areas with a high density of substance White.

The globe pallus is usually divided into two parts: the internal or medial and the external or laterall. The globus pallidus receives outflows from the striatum and projects afferents to the thalamus, which will send them to the prefrontal cortex. The outer part contains GABAergic neurons and acts in conjunction with the subthalamic nucleus.

Functions of the globe pallidus

The main function of the globe pallidus is the regulation of non-conscious movements. In this sense, their role consists of modulate the excitatory impulses of the cerebellum via neurotransmitter synapse GABA, the most relevant inhibitory compound of the nervous system.

The joint action of the cerebellum and the pallidum allows maintaining posture and performing harmonious movements. If the pale globe does not function properly, there is an impairment of gait, manual motor skills, and many other ordinary behaviors.

This role is mainly due to the internal globe pallidus and its connections with higher brain structures. This region of the pale rreceives afferents from the striatum coming from the basal ganglia and sends them to the thalamus, which regulates basic bodily functions such as alertness and sleep and allows sensory and motor information to reach the cortex.

The lateral part of the pallidum, in conjunction with the subthalamic nucleus, is involved in the regulation of physiological rhythms of the organism, especially in relation to the rest of the structures of the basal ganglia.

Related disorders

Lesions in the globe pallidus cause motor disturbances by disrupting the extrapyramidal pathway connections. Thus, the affectation of this structure can cause symptoms such as tremors, spasms, bradykinesia (slowness of movement), stiffness, dystonia (uncontrollable contractions), seizures or ataxia (lack of muscle coordination).

The disorder most clearly associated with damage to the globe pallidus is Parkinson's disease, which causes degeneration of the subcortical structures, including the basal ganglia.

Some typical symptoms of Parkinson's, such as tremors at rest, muscle stiffness and postural problems, are explained by the lesion of the pallidum and / or the cerebellum. However, as this disease progresses it also causes lesions in other parts of the brain; this is the cause of the progressive cognitive decline found in these patients.