Nigrostriatal pathway of the brain: structures and functions
Jul 15, 2021
The dopamine It is one of the main neurotransmitters in the brain, known above all for its involvement in processes related to pleasure and reward systems. However, its role in motor control is fundamental, using the different dopaminergic pathways to travel through the brain.
One of these neural networks is the nigrostriatal pathway. Throughout this article we will talk about what structures compose it, as well as its role in brain function and the clinical implications that its deterioration entails.
- Related article: "Parts of the human brain (and functions)"
What is the nigrostriatal pathway?
The nigrostriatal pathway is one of the four pathways that make up the dopaminergic system. Together with the mesolimbic pathway, the mesocortical pathway and the tuberoinfundibular pathway, it is responsible for transporting dopamine from one place to another in the brain.
To be more exact, the nigrostriatal pathway is one whose beams project from the substantia nigra to the striatum, specifically the caudate nucleus and the putamen.
The injuries or alterations typical of disorders such as Parkinson's disease or choreas affect the nigrostriatal pathway, generating numerous symptoms. Likewise, dopamine D2 antagonists can induce extrapyramidal symptoms associated with pseudoparkinsonism.
As mentioned above, the nigrostriatal pathway runs through the brain from the substantia nigra to the caudate nucleus and putamen, located in the striatum.
1. Black substance
The substantia nigra corresponds to a brain area located in the midbrain, which stores dopamine-producing neurons. It receives the name of black substance since its tone is darker than that of the rest of the areas that surround it, because its neuromelanin levels are the highest in the area.
The main function of the substantia nigra is related to eye movements, motor control, reward seeking, learning and addiction. However, most of them are also mediated by the striatum.
When this structure begins to disintegrate or begins a process of degeneration, conditions such as Parkinson's disease appear, which leads to numerous motor and cognitive disorders.
2. Striated body
Also called the striated nucleus, the striatum forms the subcortical part of the telencephalon. This structure is distinguished by being essential when transmitting information to the basal ganglia.
The set of structures that make up the striatum are the caudate nucleus, the putamen and the nucleus accumbens. However, in this article only the former will be described as they are an essential part of the functioning of the nigrostriatal pathway.
- Related article: "Striatum: structure, functions and associated disorders"
3. Caudate nucleus
The structures known as caudate nuclei are located approximately in the center of the brain, very close to the thalamus. We speak of nuclei in the plural because there are two different nuclei inside each of the hemispheres of the brain.
Traditionally, the basal ganglia have been associated with higher-order motor control. Within these functions, the caudate nucleus participates in the domain of voluntary control, as well as in learning and memory processes.
The putamen is a system also located in the central area of the brain, which plays a role essential in the control of movements, specifically in the control and direction of voluntary movements fine.
In addition, the correct functioning of the putamen exerts an important influence on operant conditioning and recent studies label it as the origin of feelings of love and hate.
- Related article: "Putamen: structure, functions, and related disorders"
Role in brain function
As we have seen, the nigrostriatal pathway, and those structures that make it up, are responsible for govern and favor the control of voluntary movements.
In general, movement control is the result of the successful combination of sensory information and motor information coordinated by the central nervous system (CNS).
Within this motor control we find voluntary movements, involuntary movements and reflexes. However, in this case, it is the voluntary movements that are controlled by the nigrostriatal route.
Voluntary movements are carried out with the intention of achieving a goal, that is, they are purposeful. What's more, most of these movements can be learned and improved through practice
Clinical implications and associated disorders
Knowing the structures related to the mesocortical pathway and the functions it performs, we will much easier to understand the effects or consequences of the decrease in activity on these networks neuronal.
This decrease in the level of activity can occur either by the administration of dopaminergic D2 antagonist drugs or by progressive degeneration of the road, which gives rise to diseases such as choreas or Parkinson's disease.
D2 antagonists are commonly used in the treatment of gastric problems such as nausea, vomiting or gastrointestinal problems. However, its action as a dopamine antagonist can cause unwanted extrapyramidal effects such as dystonia or pseudo-Parkinson's movements.
Choreas are a group of neurological conditions that are distinguished by causing a series of strange involuntary movements in the feet and hands in people. These impulses are caused by a series of intermittent and uneven muscle contractions, that is, they do not present a repetitive or rhythmic pattern, but rather seem to be transmitted from one muscle or another.
Within this group is the well-known Huntington's chorea, benign familial chorea or familial inverted choreoathetosis.
Parkinson's disease is a relatively common motor disorder in people over 60 years of age. The origin of this disease is found in a decrease in the production of dopamine, especially in the nigrostriatal pathway, which is no longer sufficient to supply the demands of the brain.
It is a disease that develops progressively, first affecting one side of the body and then acting on the other. The main symptoms of this disease are:
- Tremors in upper and lower extremities, hands, feet, jaw and face.
- Tightening of the muscles of the arms, legs and trunk.
- Slowness of movement
- Disturbances in balance and coordination.