Although not as well known to most people as the brain lobes, the subcortical regions of the brain perform equally important functions. In particular, the areas we know as the basal ganglia are critical for movement, among other things.
One of the nuclei that form the basal ganglia is the globus pallidus, the smallest of all. In the following we will see the structure and functions of the globus pallidus , as well as the disorders that are related to lesions in this region, among which Parkinson’s disease stands out.
What is the pale balloon?
The globus pallidus is also known as a paleoestriatum . It is a subcortical structure composed of gray substance (i.e., somas of neurons, dendrites without myelin and glial cells) that develops from the diencephalon, although it is part of the telencephalon. It is therefore 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 mainly to the lower motor neurons of the spinal cord that deal with movement, reflexes and posture.
This structure is more developed in primates than in other animals ; in particular, the inner region of the pale glob is only found in humans and in our closest relatives.
The basal ganglia
The pallid is one of the structures that constitute the basal ganglia, a set of closely related subcortical nuclei that are located around the third ventricle. The basal ganglia perform functions related mainly to voluntary and automatic movements.
The nuclei that form the basal ganglia , in addition to the globus pallidus, 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 fine motor control; part of the brain’s reward system because it has many dopaminergic synapses.
- Nucleus accumbens: as 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 the automated movements, especially those of the face and the extremities.
- Subthalamic nucleus : connects the midbrain and the thalamus and regulates motor skills.
- Red substance : this region is important for coordination in general and that of the upper limbs in particular.
Structure and anatomy
The globus pallidus is mainly composed of very large neurons with a large number of dendritic branches. The appearance of the globus pallidus is peculiar because of the abundance of dendrites and its 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 basal ganglia with the globus pallidus, giving it the characteristic whitish tone of the brain areas with high density of white substance.
The pale balloon is usually divided into two parts: the internal or medial part and the external or latera part l . The inner pale glob receives efferences from the striated body and projects afferences to the thalamus, which will send them to the prefrontal cortex. The external part contains gabaergic neurons and acts in conjunction with the subthalamic nucleus.
Functions of the Pale Balloon
The main function of the globus pallidus is the regulation of unconscious movements. In this sense, its role consists in modulating the excitatory impulses of the cerebellum by means of synapses of the neurotransmitter GABA, the most relevant inhibitory compound of the nervous system.
The joint action of the cerebellum and the palate allows the maintenance of posture and the realization of harmonious movements . If the globus pallidus does not function properly, this affects walking, manual movement and many other ordinary behaviours.
This role is mainly due to the pale inner globe and its connections to higher brain structures. This region of the pallidus r receives afferences from the striated body from the basal ganglia and sends them to the thalamus, which regulates basic body functions such as alertness and sleep and allows sensory and motor information to reach the cortex.
The lateral part of the pallid, in conjunction with the subthalamic nucleus, intervenes in the regulation of the physiological rhythms of the organism, especially in relation to the other structures of the basal ganglia.
Injuries to the globus pallidus cause motor disorders as they interrupt the connections of the extrapyramidal pathways. Thus, the involvement of this structure can cause symptoms such as tremors, spasms , bradykinesia (slowness of movement), stiffness, dystonia (uncontrollable contractions), convulsions or ataxia (lack of muscle coordination).
The disorder most clearly associated with damage to the globus pallidus is Parkinson’s disease, which causes a degeneration of subcortical structures, including the basal ganglia.
Some typical symptoms of Parkinson’s , such as resting tremors, muscle stiffness and postural problems, are explained by the lesion of the palate and/or the cerebellum. However, as the disease progresses, it causes lesions in other parts of the brain as well; this is the cause of the progressive cognitive impairment found in these patients.