Brain a human being is a complex and subtle substance that is responsible for the regulation of the whole organism.
The structure and features of the functioning of this organ have not yet been fully studied, scientists are discovering new features every day that allow the brain to work. But about such a part as the substantia nigra of the brain or substantia nigra has been known for a long time.
What is the substantia nigra and where is it located?
The substance is one of the oldest parts in the structure of the brain, located in its core - the quadruple of the midbrain. Historically, she was responsible for the movements of our ancestors, then, when they became more complex, the structure also changed. The black matter was overgrown with nerve connections, forming a more complex structure.
The black substance got its name due to the action of a pigment - neuromelanin, which stains cells in a dark color. The black matter of the midbrain is heterogeneous, it is divided into two halves: right and left. In addition, two layers are distinguished in the substance: ventral and compact. The ventral is closer to the front of the head, and the compact is to the back. The first provides the synthesis of a neurotransmitter
dopamine, the second is engaged in processing incoming information and transferring it to other structures.Ultrasound of the substantia nigra of the brain shows that it is associated with all departments, but most closely - with the basal ganglia and visual hillocks.
An abundant supply of blood speaks of the high role of the structure in the activity of the body. Among the functions of the substantia nigra are:
- the implementation of elementary movements: swallowing, chewing, breathing, eye movements and others;
- regulation of small and precise movements of the limbs;
- help in expressing emotions;
- participation in emotional processes;
- provoking some mental disorders.
The role of the substance in the development of pathologies
The role of the substance in the development of mental illness is great. It contains neurons, the processes of which diverge throughout the brain, affecting the legs of the brain and the inner capsule.
Their endings, containing terminal microvesicles that produce dopamine, are located in neostriatum. Any damage to this structure leads to impairments in motor and psychoemotional functions.
Schizophrenia
Development mechanism schizophrenia has been studied for many years, but researchers have not come to a consensus. Various theories of the formation of this disease have been put forward, one of which links schizophrenia with disorders in the work of the substantia nigra, the nucleus of which is located in the midbrain. This is the so-called dopamine hypothesis.
Studies show that patients with schizophrenia have abnormalities in the synthesis and perception of dopamine.
So, they manifest:
- increased production of the hormone;
- an increase in the concentration of dopamine in synapses;
- increased production serotonin;
- greater volume of dopamine released when exposed to amphetamines.
Such hypersensitivity contributes to the overstimulation of neurons in the brain and its overexcitation. The patient is unable to control the stream of consciousness, and his perception of the surrounding reality changes. Similar conditions occur when taking psychotropic substances, which in healthy people cause hallucinations and other abnormalities, and have a much stronger effect on patients.
According to statistics, the development of schizophrenia affects more men than women. In the former, it usually develops earlier and is more severe. For women, the manifestation of symptoms is characteristic at the age of 25-30 years.
Transcranial Doppler The substantia nigra allowed us to examine its structure and find that in schizophrenia, changes in the dopamine system affect the associative striatum more than the limbic one.
Moreover, deviations in the synthesis of dopamine by neurons in the direction of increasing its production are observed even before the development of the disease. But the higher these deviations, the greater the likelihood of contracting schizophrenia.
Scientists cite several reasons for their appearance:
- disturbances in the control system of the influence of the hippocampus on the dopamine pathway;
- changes in the structure of neurons that produce a neurotransmitter;
- malfunctions of cortical structures that affect the dopamine systems;
- the impact of other neurotransmitter systems.
Thus, changes in the functioning of the dopamine system are observed in all cases of schizophrenia. However, the influence of other brain structures is not excluded.
Treatment based on blocking receptors or inhibiting dopamine production is generally beneficial. Patients are offered antipsychotic drugs that block the action of dopamine, although they have a serious consequence - depressive conditions. Cognitive-behavioral psychotherapy, which can be performed by a psychologist, is safer.
Parkinson's disease
At Parkinson's disease damage occurs to dopaminergic neurons located in the compact part of the substantia nigra, in which aggregation occurs Levi's calf all over the brain.
In this case, strong motor, psychopathological and cognitive abnormalities arise:
- slowing down of movement;
- decrease or absence of facial expressions;
- tremor;
- the predominance of flexion posture;
- the complexity of the transition from a state of rest to a state of movement;
- memory impairment;
- dementia and others.
The disease develops mainly in men over the age of 60, women suffer from this pathology less often. The reason is changes in the dopamine system, which can be caused by both poisoning with toxic substances and taking certain medications. In addition, the disease develops without "apparent" reasons, the source of which has not yet been found. Many facts indicate a hereditary predisposition to Parkinson's disease.
Scientists suggest that the destruction of neurons in the peripheral nervous system begins, and then goes to the brain stem and moves to the middle and anterior. Confirmation of this theory is found in the alteration of cholinergic neurotransmission observed in patients with a mild form of the disease.
When 30 percent of the neurons that produce dopamine are damaged, its deficiency occurs and the symptoms of the disease develop. Its distribution is uneven and usually progresses in the direction from the back of the black matter to the front.
Studies have also found the neurotoxin MPTP, which destroys dopamine neurons. It is important to understand the source of its products and try to limit it.
The use of therapy with the use of L-dopa, an intermediate element in the scheme for obtaining dopamine, gives a positive result in terms of inhibiting the disease. However, it does not allow to restore the lost structures of the brain. In addition, with the progression of Parkinson's disease, the effectiveness of this therapy decreases markedly.
Damage consequences
The neurons of the substantia nigra of the midbrain produce neurotransmitters, the main of which is dopamine. It acts as a means of “rewarding” the brain, inducing feelings of pleasure and influencing a person's motivation and learning.
In case of disturbances in the structure of the substantia nigra or the ways of its connection with other structures of the brain, changes in the work of the brain are possible, which manifests itself in the form of severe disorders of motor function:
- tremors;
- muscle hypertension;
- chorea;
- athetosis;
- monotonous and deaf speech;
- hypokinesia;
- hypomimia and others.
These violations accompany mental illness:
- parkinsonism;
- akathisia;
- dystonia;
- schizophrenia and others.
Role in neuropharmacology and toxicology
The substantia nigra affects the red core, causing feelings of satisfaction with the result and pleasure. This allows the person to reinforce skills and activities that are enjoyable and rewarding. However, they may not always be safe.
So, the use of psychotropic drugs or drugs causes a large surge in dopamine and, as a result, pleasure. In an attempt to repeat it, the person begins to use the stimulant regularly. However, such surges are compensated by the nervous system and the so-called tolerance is developed - reduced sensitivity to the action of the substance. As a result, the level of pleasure gradually decreases, but the desire to obtain it remains.
This and other features of the action of chemicals, including drugs, are being investigated in neuropharmacology and toxicology.
Among the studied components are such as:
- cocaine;
- amphetamines;
- MPTP;
- Levodop.
Cocaine and amphetamine are dopamine-enhancing and addictive substances. In addition, they can "push" the development of schizophrenia.
The latter is used in the treatment of Parkinson's disease, is quite effective in eliminating symptoms, but does not give a result in restoring lost structures.
MPTP stands for Methyl Phenyltetrahydropyridine, it refers to neurotoxins that directly reduce dopamine production. Now used by scientists to model disease in animals in an attempt to understand the mechanism of its development.
