Black matter of the brain. The structure of the midbrain

Also known as black matter, black core.

Latin name: substantia nigra

Already from the name it follows that the main distinctive feature of this section of the brain stem is its color. The pigment melanin, namely neuromelanin, is responsible for the dark color of this neuronal cluster. Due to uniform staining, this area is often accepted as an integral component, but this is not so. The substantia nigra has a compact part and a reticular part.

Substance black in the brain

In the midbrain, the black substance is located more ventrally, in the legs of the brain. It fills them over the entire height, and in diameter it makes up its middle third. The cells of the compact layer are located dorsally in relation to the cells that make up the reticular layer.

If we talk about fibers, axons of nerves passing through the substantia nigra, it is necessary to consider the entire complex of the extrapyramidal system. It becomes easier to understand the interactions of the black substance, the striopallidary system, and the reticular formation if one remembers the processes of phylogenesis and evolution.

Evolution

It is no secret that in the process of phylogenesis, the brain "overgrown" with nervous structures and connections. So, the extrapyramidal system is the ancient brain. This system innervated the movements (which were elementary) of our distant ancestors. In the process of evolution, both the movements and the structure of the brain became more complex.

Previously, the paleostriatum (the very first extrapyramidal system) was enough to serve the movements, which included a pale ball that gave fibers through the black substance and the reticular formation to the spinal cord and further along the target muscles.

Growing, the brain acquired such structures as the caudate nucleus and the shell - the neostriatum. If in many mammals this system is still able to support some movements without the involvement of the pyramidal system (which has been experimentally proven), then in humans this ability of the extrapyramidal system is reduced.

Functions

In the human brain, the black substance performs an additional function, bringing our movements to smoothness, allowing them to be more voluminous, precise, allowing us to stay static in certain positions, quickly change them, which, for example, allows us to express emotions.

Ultimately, the role of the black substance is the regulation of the extrapyramidal system, the impact on it from the inside due to the fibers that mainly pass through the compact part.

In addition, without black substance, such important functions as swallowing, chewing and even breathing would be impossible.

tracts

All fibers passing through the substantia nigra can be divided into two large groups: afferent and efferent.

Pathways of fibers passing through the substantia nigra of the midbrain:

• Straight way. It starts from the cerebral cortex, then enters and continues to move from the striatum to the reticular part of the substantia nigra, after which it reaches the medial globus pallidus. The signal then travels through the thalamus to the motor cortex. It is formed by GABAergic fibers and, as a result, inhibitory.
• Indirect path. Cerebral cortex - striatum - lateral globus pallidus - subthalamic nucleus - reticular part of the substantia nigra - medial globus pallidum - thalamus - motor cortex. In this case, part of the fibers from the subthalamic nucleus come to the lateral pale ball. GABAergic fibers tend to the subthalamic nucleus, while glutamatergic and, therefore, excitatory fibers move further.
• dopaminergic pathway. The main fibers passing through the compact part of the substantia nigra connect the caudate nucleus and the putamen (striatum). For this reason, the path is also called nigrostriatal.

The direct and indirect paths together are part of the cortico-striate-pallido-thalamocortical circle. The dopaminergic pathway plays the role of a modulator in it.

Defeats

The dopaminergic pathway of the compact substantia nigra has the greatest clinical significance. The pathology of this part of the trunk (impaired production of dopamine, the appearance of Lewy bodies in the synapses) leads to a violation of the relationship between the sections of the striopallidary system and the appearance of such a symptom complex as parkinsonism. The clinical picture is represented by a triad of symptoms.

There are many scientific synonyms for this condition, which is characteristic of Parkinson's disease. Here are some syndromes: akinetic-rigid, amyostatic, hypokinetic-hypertonic, pallidonigral.

Triad of symptoms:

• akinesis, hypokinesis- manifested by slow movements, limited in volume. The exact pathogenesis of a particular symptom remains unclear.
• rigidity- decreased muscle tone
• tremor- antagonistic tremor increases at rest, weakens with purposeful movements.

On its ventral surface there are two massive bundles nerve fibers- legs of the brain, along which signals are carried from the cortex to the underlying structures of the brain.

Rice. 1. The most important structural formations of the midbrain (cross section)

In the midbrain, there are various structural formations: the quadrigemina, the red nucleus, the substantia nigra, and the nuclei of the oculomotor and trochlear nerves. Each formation performs a specific role and contributes to the regulation of a number of adaptive reactions. Through midbrain all ascending paths pass, transmitting impulses to the thalamus, cerebral hemispheres and cerebellum, and descending paths, conducting impulses to the medulla oblongata and spinal cord. The neurons of the midbrain receive impulses through the spinal and medulla oblongata from the muscles, visual and auditory receptors along the afferent nerves.

Anterior colliculi are the primary visual centers, and they receive information from the visual receptors. With the participation of the anterior tubercles, visual orienting and watchdog reflexes are carried out by moving the eyes and turning the head in the direction of the action of visual stimuli. The neurons of the posterior tubercles of the quadrigemina form the primary auditory centers and when receiving excitation from auditory receptors, they ensure the implementation of auditory orienting and sentinel reflexes (in the animal, auricles, it becomes alert and turns its head towards the new sound). The nuclei of the posterior tubercles of the quadrigemina provide a sentinel adaptive reaction to a new sound stimulus: redistribution of muscle tone, increased tone of the flexors, increased heart rate and respiration, increased blood pressure, i.e. the animal prepares for defense, flight, attack.

black substance receives information from muscle receptors and tactile receptors. It is associated with the striatum and the globus pallidus. Neurons of the substantia nigra are involved in the formation of an action program that coordinates the complex acts of chewing, swallowing, as well as muscle tone and motor reactions.

red core receives impulses from muscle receptors, from the cerebral cortex, subcortical nuclei and cerebellum. Has a regulatory effect on motor neurons spinal cord through the nucleus of Deiters and the rubrospinal tract. The neurons of the red nucleus have numerous connections with the reticular formation of the brain stem and, together with it, regulate muscle tone. The red nucleus has an inhibitory effect on the extensor muscles and an activating effect on the flexor muscles.

Elimination of the connection of the red nucleus with the reticular formation of the upper part medulla oblongata causes a sharp increase in the tone of the extensor muscles. This phenomenon is called decerebrate rigidity.

The structures of the midbrain are directly involved in the integration of heterogeneous signals necessary for the coordination of movements. With the direct participation of the red nucleus, the black substance of the midbrain, the neural network of the stem movement generator and, in particular, the eye movement generator, is formed.

Based on the analysis of signals entering the stem structures from proprioreceptors, vestibular, auditory, visual, tactile, pain and others sensory systems, in the stem generator of movements, a stream of efferent motor commands is formed, sent to the spinal cord along descending pathways: rubrospinal, retculospinal, vestibulospinal, tectospinal. In accordance with the commands developed in the brain stem, it becomes possible not only to contract individual muscles or muscle groups, but to form a certain body posture, maintain body balance in various postures, perform reflex and adaptive movements during exercise. various kinds body movements in space (Fig. 2).

Rice. 2. The location of some nuclei in the brain stem and hypothalamus (R. Schmidt, G. Thews, 1985): 1 - paraventricular; 2 - dorsomedial: 3 - preoptic; 4 - supraoptic; 5 - back

The structures of the stem movement generator can be activated by arbitrary commands that come from the motor areas of the cerebral cortex. Their activity can be enhanced or inhibited by signals from sensory systems and the cerebellum. These signals can modify already running motor programs so that their execution changes to meet new requirements. So, for example, the adaptation of a posture to purposeful movements (as well as the organization of such movements) is possible only with the participation of the motor centers of the cerebral cortex.

The red nucleus plays an important role in the integrative processes of the midbrain and its stem. Its neurons are directly involved in the regulation, distribution of skeletal muscle tone and movements that ensure the preservation of the normal position of the body in space and the adoption of a posture that creates readiness to perform certain actions. These influences of the red nucleus on the spinal cord are realized through the rubrospinal tract, the fibers of which terminate in intercalary neurons spinal cord and have an excitatory effect on the a- and y-motor neurons of the flexors and inhibit most of the neurons of the extensor muscles.

The role of the red nucleus in the distribution of muscle tone and maintaining body posture is well demonstrated in animal experiments. When the brainstem is cut (decerebrated) at the level of the midbrain below the red nucleus, a condition develops called decerebrate rigidity. The limbs of the animal become straightened and tense, the head and tail are thrown back to the back. This position of the body occurs due to an imbalance between the tone of the antagonist muscles in the direction of a sharp predominance of the extensor tone. After transection, the inhibitory effect of the red nucleus and the cerebral cortex on the extensor muscles is eliminated, and the excitatory effect of the reticular and vestibular (Deigers) nuclei on them remains unchanged.

Decerebrate rigidity occurs immediately after crossing the brainstem below the level of the red nucleus. In the origin of rigidity, the y-loop is of paramount importance. Rigidity disappears after the intersection of the posterior roots and the cessation of the influx of afferent nerve impulses to the neurons of the spinal cord from the muscle spindles.

The vestibular system is related to the origin of rigidity. Destruction of the lateral vestibular nucleus eliminates or reduces the tone of the extensors.

In the implementation of the integrative functions of the structures of the brain stem, an important role is played by the substantia nigra, which is involved in the regulation of muscle tone, posture and movements. It is involved in the integration of signals necessary to coordinate the work of many muscles involved in the acts of chewing and swallowing, and affects the formation of respiratory movements.

Through the substantia nigra, the motor processes initiated by the stem generator of movements are influenced by the basal ganglia. There are two-way connections between the substantia nigra and the basal ganglia. There is a bundle of fibers that conducts nerve impulses from the striatum to the substantia nigra, and a path that conducts impulses in the opposite direction.

The substantia nigra also sends signals to the nuclei of the thalamus, and further along the axons of the thalamic neurons, these signal flows reach the cortex. Thus, the substantia nigra participates in the closing of one of the neural circuits through which signals circulate between the cortex and subcortical formations.

The functioning of the red nucleus, the substantia nigra and other structures of the stem movement generator is controlled by the cerebral cortex. Its influence is carried out both through direct connections with many stem nuclei, and indirectly through the cerebellum, which sends bundles of efferent fibers to the red nucleus and other stem nuclei.

midbrain comprises:

Mound of the quadrigemina,

red core,

black substance,

Seam core.

red core- provides skeletal muscle tone, redistribution of tone when changing posture. Just stretching is a powerful work of the brain and spinal cord, for which the red nucleus is responsible. The red core ensures the normal tone of our muscles. If the red nucleus is destroyed, decerebration rigidity occurs, while the tone sharply increases in some animals of the flexors, in others - of the extensors. And with absolute destruction, both tones increase at once, and it all depends on which muscles are stronger.

black substance– How is the excitation from one neuron transmitted to another neuron? Excitation occurs - this is a bioelectric process. He reached the end of the axon, where it stands out Chemical substance- mediator. Each cell has its own mediator. The neurotransmitter is produced in the substantia nigra in nerve cells dopamine. When the substantia nigra is destroyed, Parkinson's disease occurs (fingers, head constantly tremble, or there is stiffness as a result of a constant signal going to the muscles) because there is not enough dopamine in the brain. The substantia nigra provides subtle instrumental movements of the fingers and influences all motor functions. The substantia nigra exerts an inhibitory effect on the motor cortex through the stripolidar system. In case of violation, it is impossible to perform fine operations and Parkinson's disease (stiffness, tremor) occurs.

Above - the anterior tubercles of the quadrigemina, and below - the posterior tubercles of the quadrigemina. We look with our eyes, but we see with the occipital cortex of the cerebral hemispheres, where the visual field is located, where the image is formed. A nerve departs from the eye, passes through a series of subcortical formations, reaches the visual cortex, there is no visual cortex, and we will not see anything. Anterior colliculi is the primary visual area. With their participation, an orienting reaction to a visual signal occurs. The orienting response is “what is the response?” If the anterior tubercles of the quadrigemina are destroyed, vision will be preserved, but there will be no quick reaction to the visual signal.

Posterior tubercles of the quadrigemina This is the primary hearing area. With its participation, an orienting reaction to a sound signal occurs. If the posterior tubercles of the quadrigemina are destroyed, hearing will be preserved but there will be no orienting reaction.

Seam cores is the source of another mediator serotonin. This structure and this mediator takes part in the process of falling asleep. If the nuclei of the suture are destroyed, then the animal is in a constant state of wakefulness and quickly dies. In addition, serotonin is involved in learning with positive reinforcement (this is when a rat is given cheese). Serotonin provides such character traits as forgiveness, goodwill, in aggressive people there is a lack of serotonin in the brain.

12) Thalamus - a collector of afferent impulses. Specific and nonspecific nuclei of the thalamus. The thalamus is the center of pain sensitivity.

thalamus- visual tubercle. They were the first to discover in him a relation to visual impulses. It is a collector of afferent impulses, those that come from receptors. The thalamus receives signals from all receptors, except for the olfactory ones. Infa enters the thalamus from the cortex, from the cerebellum and from the basal ganglia. At the level of the thalamus, these signals are processed, only the most important information for a person at the moment is selected, which then enters the cortex. The thalamus consists of several dozen nuclei. The nuclei of the thalamus are divided into two groups: specific and nonspecific. Through specific nuclei of the thalamus, signals arrive strictly to certain areas of the cortex, for example, visual to the occipital, auditory to the temporal lobe. And through non-specific nuclei, information diffusely enters the entire cortex in order to increase its excitability in order to more clearly perceive specific information. They prepare the bp cortex for the perception of specific information. The highest center of pain sensitivity is the thalamus. The thalamus is the highest center of pain sensitivity. Pain is necessarily formed with the participation of the thalamus, and with the destruction of some nuclei of the thalamus, pain sensitivity is completely lost, with the destruction of other nuclei, barely tolerable pain occurs (for example, phantom pains are formed - pain in the missing limb).

13) Hypothalamo-pituitary system. The hypothalamus is the control center endocrine system and motivations.

The hypothalamus and pituitary gland form a single hypothalamic-pituitary system.

Hypothalamus. The pituitary stalk departs from the hypothalamus, on which it hangs pituitary- the main endocrine gland. The pituitary gland regulates the work of other endocrine glands. The hypoplamus is connected to the pituitary gland by nerve pathways and blood vessels. The hypothalamus regulates the work of the pituitary gland, and through it the work of other endocrine glands. The pituitary gland is divided into adenohypophysis(glandular) and neurohypophysis. In the hypothalamus (this is not an endocrine gland, this is a part of the brain) there are neurosecretory cells in which hormones are secreted. This is a nerve cell, it can be excited, it can be inhibited, and at the same time hormones are secreted in it. An axon departs from it. And if these are hormones, they are released into the blood, and then it goes to the decision organs, that is, to the organ whose work it regulates. Two hormones:

- vasopressin - contributes to the preservation of water in the body, it acts on the kidneys, with its deficiency, dehydration occurs;

- oxytocin - is produced here, but in other cells, provides contraction of the uterus during childbirth.

Hormones are secreted in the hypothalamus and secreted by the pituitary gland. Thus, the hypothalamus is connected to the pituitary gland by neural pathways. On the other hand: nothing is produced in the neurohypophysis, hormones come here, but the adenohypophysis has its own glandular cells, where a number of important hormones are produced:

- ganadotropic hormone - regulates the work of the sex glands;

- thyroid-stimulating hormone - regulates work thyroid gland;

- adrenocorticotropic - regulates the work of the adrenal cortex;

- growth hormone, or a growth hormone, - ensures the growth of bone tissue and the development of muscle tissue;

- melanotropic hormone - is responsible for pigmentation in fish and amphibians, in humans it affects the retina.

All hormones are synthesized from a precursor called pro-opiomelanocortin. A large molecule is synthesized, which is cleaved by enzymes, and other hormones smaller in the number of amino acids are released from it. Neuroendocrinology.

The hypothalamus contains neurosecretory cells. They produce hormones:

1) ADG (antidiuretic hormone regulates the amount of urine excreted)

2) oxytocin (provides contraction of the uterus during childbirth).

3) statins

4) liberals

5) thyroid-stimulating hormone affects the production of thyroid hormones (thyroxine, triiodothyronine)

Thyroliberin -> thyroid stimulating hormone -> thyroxine -> triiodothyronine.

The blood vessel enters the hypothalamus, where it branches into capillaries, then the capillaries gather and this vessel passes through the pituitary stalk, branches again in the glandular cells, exits the pituitary gland and carries with it all these hormones, which each go with the blood to its own gland. Why do we need this "wonderful vascular network"? There are nerve cells in the hypothalamus that terminate in the blood vessels of this wonderful vasculature. These cells produce statins and liberals - this is neurohormones. Statins inhibit the production of hormones in the pituitary gland, and liberals reinforce it. If an excess of growth hormone causes gigantism, this can be stopped with samamatostatin. On the contrary: the dwarf is injected with samatoliberin. And apparently for any hormone there are such neurohormones, but they are not yet open. For example, thyroid, thyroxine is produced in it, and in order to regulate its production in the pituitary gland, thyrotropic hormone, and in order to control thyroid-stimulating hormone, thyreostatin was not found, but thyroliberin is used perfectly. Although these are hormones, they are produced in nerve cells, therefore, in addition to endocrine effects, they have a wide range of extra-endocrine functions. Thyreoliberin is called panactivin, because it improves mood, increases efficiency, normalizes blood pressure, accelerates healing in case of spinal cord injuries, it cannot be used alone for disorders in the thyroid gland.

Previously, the functions associated with neurosecretory cells and cells that produce neurofebtides have been considered.

The hypothalamus produces statins and liberins, which are included in the body's stress response. If the body is affected by some harmful factor, then the body must somehow respond - this is the stress reaction of the body. It cannot proceed without the participation of statins and liberins, which are produced in the hypothalamus. The hypothalamus is necessarily involved in the response to stress.

The next function of the hypothalamus is:

It contains nerve cells that are sensitive to steroid hormones, that is, sex hormones to both female and male sex hormones. This sensitivity provides the formation of the female or male type. The hypothalamus creates the conditions for motivating behavior according to the male or female type.

A very important function is thermoregulation, in the hypothalamus there are cells that are sensitive to blood temperature. Body temperature can change depending on the environment. Blood flows through all brain structures, but thermoreceptive cells that pick up the slightest change temperatures are found only in the hypothalamus. The hypothalamus turns on and organizes two body responses, either heat production or heat loss.

food motivation. Why does a person feel hungry?

The signal system is the level of glucose in the blood, it should be constant ~ 120 milligrams % - s.

There is a mechanism of self-regulation: if our blood glucose level decreases, liver glycogen begins to break down. On the other hand, glycogen stores are not enough. In the hypothalamus there are glucoreceptor cells, i.e. cells that register the level of glucose in the blood. Glucoreceptor cells form hunger centers in the hypothalamus. When the blood glucose level drops, these blood glucose-sensitive cells become excited, and a feeling of hunger occurs. At the level of the hypothalamus, only food motivation arises - a feeling of hunger, in order to search for food, the cerebral cortex must be connected, with its participation a true food reaction occurs.

The satiety center is also located in the hypothalamus, it inhibits the feeling of hunger, which prevents us from overeating. When the satiety center is destroyed, overeating occurs and, as a result, bulimia.

The hypothalamus also has a thirst center - osmoreceptive cells (osmotic pressure depends on the concentration of salts in the blood). Osmoreceptive cells register the level of salts in the blood. With an increase in salts in the blood, osmoreceptive cells are excited, and drinking motivation (reaction) occurs.

The hypothalamus is the highest center of regulation of the autonomic nervous system.

The anterior hypothalamus mainly regulates the parasympathetic nervous system, while the posterior hypothalamus regulates the sympathetic nervous system.

The hypothalamus provides only motivation and purposeful behavior of the cerebral cortex.

14) Neuron - structural features and functions. Differences between neurons and other cells. Glia, blood-brain barrier, cerebrospinal fluid.

I First, as we have already noted, in their diversity. Every nerve cell consists of a body - catfish and offshoots. Neurons are different:

1. by size (from 20 nm to 100 nm) and shape of the soma

2. by the number and degree of branching of short processes.

3. according to the structure, length and branching of axon endings (laterals)

4. by the number of spines

II Neurons also differ in functions:

a) perceiving information from the external environment

b) transmitting information to the periphery

in) processing and transmit information within the CNS,

G) exciting,

e) brake.

III Differ in chemical composition : a variety of proteins, lipids, enzymes are synthesized and, most importantly, - mediators .

WHY, WITH WHAT FEATURES IS IT RELATED TO?

This variety is defined high activity of the genetic apparatus neurons. During neuronal induction, under the influence of neuronal growth factor, NEW GENES are switched on in the cells of the ectoderm of the embryo, which are characteristic only for neurons. These genes provide the following features of neurons ( the most important properties):

A) The ability to perceive, process, store and reproduce information

B) DEEP SPECIALIZATION:

0. Synthesis of specific RNA;

1. No reduplication DNA.

2. Proportion of genes capable of transcriptions, make up in neurons 18-20%, and in some cells 40% (in other cells - 2-6%)

3. Ability to synthesize specific proteins (up to 100 in one cell)

4. The uniqueness of the lipid composition

C) Food Privilege => Level Dependence oxygen and glucose in blood.

Not a single tissue in the body is in such a dramatic dependence on the level of oxygen in the blood: 5-6 minutes of respiratory arrest and the most important structures of the brain die, and first of all - the cerebral cortex. A decrease in glucose levels below 0.11% or 80 mg% - hypoglycemia may occur and then coma.

And on the other hand, the brain is fenced off from the blood flow of the BBB. He does not let anything that could harm them into the cells. But, unfortunately, not all - many low-molecular toxic substances pass through the BBB. And pharmacologists always have a task: does this drug pass through the BBB? In some cases, this is necessary when it comes to diseases of the brain, in others it is indifferent to the patient if the drug does not damage nerve cells, and in still others this should be avoided. (NANOPARTICLES, ONCOLOGY).

Sympathetic NS is excited and stimulates the work of the adrenal medulla - the production of adrenaline; in the pancreas - glucagon - breaks down glycogen in the kidneys to glucose; glucocarticoids produced. in the adrenal cortex - provides gluconeogenesis - the formation of glucose from ...)

And yet, with all the variety of neurons, they can be divided into three groups: afferent, efferent and intercalary (intermediate).

15) Afferent neurons, their functions and structure. Receptors: structure, functions, formation of an afferent volley.

black substance (SN listen)) is a basal ganglion structure located in the brain that plays an important role in reward and movement. black substance is Latin for "substance black", reflecting the fact that parts of the black substance appear darker than in neighboring areas, due to high levels of neuromelanin in dopaminergic neurons. It was discovered in 1784 by Vic d'Azire and Samuel Thomas Sömmering referred to this structure in 1791. Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta.

Although the substantia nigra appears as a continuous band in sections of the brain, anatomical studies have shown that it actually consists of two parts with very different connections and function: Pars compacta (SNPC) and Pars reticula (SNpr). This classification was first proposed in 1910. Sano pars compacta serves primarily as an output signal to the base ganglion circuit, supplying the striatum with dopamine. Pars reticulo, though, serves primarily as input, relaying signals from the basal ganglia to many other brain structures.

Compound

Scheme of the main components of the basal ganglia and their relationship

Pars geisia

Pars reticulio bears a strong structural and functional resemblance to the interior of the globus pallidus. The two are sometimes considered part of the same structure, separated by the white matter of the internal capsule. Like the globus pallidus, the neurons in Pars reticulata are mostly GABA.

Afferent connections

The main contribution to SNpr comes from the striatum. It is delivered via two routes known as direct and indirect routes. The direct pathway consists of axons from the middle spiny cells in the striatum, which project directly to Pars reticula. The indirect path consists of three links: a projection from the striated environment of spiny cells to the outer part of the pale ball; GABAergic projection from the globus pallidus to the hypothalamic nucleus and glutamatergic projection from the subthalamic nucleus to the parsa reticulum. Thus, activity in the striatum via the direct pathway has an inhibitory effect on neurons in (SNpr) but an excitatory effect via the indirect pathway. The direct and indirect pathways originate from different subsets of the striatal medial spiny cells: they are tightly intertwined but express different types dopamine receptors, and also shows other neurochemical differences.

Efferent connections

Significant projections occur to the thalamus (ventral lateral and anterior ventral nuclei), colliculus, and other caudal nuclei from the nigrothalamic pathway, which use GABA as their neurotransmitter. In addition, these neurons form up to five collaterals that branch into both pars compacta and pars reticulla, likely modulating dopaminergic activity in pars compacta.

function

The substantia nigra is an important player in brain function, specifically in eye movement, motor planning, reward-seeking, learning, and addiction. Many of the substantia nigra's effects are mediated through the striatum. The dopaminergic substantia nigra is introduced into the striatum via the nigrostriatal pathway closely related to the striatum's function. The co-dependence between the striatum and the substantia nigra can be seen as follows: with the substantia nigra electrically stimulated, no movement occurs; however, the symptoms of nigral degeneration associated with Parkinson's disease is a bitter example of the effect of substantia nigra on movement. In addition to striatum-mediated functions, substantia nigra also serves as a major source of GABAergic inhibition to various brain targets.

Pars geisia

Pars compacta

The most prominent feature of pars compacts is engine control, although the role of the substantia nigra in engine management is indirect; electrical stimulation of the substantia nigra does not result in movement, due to the mediation of the striatum in the nigral influence of movement. Pars compacta sends excitatory input to the striatum via the D1 pathway, which excites and activates the striatum, resulting in the release of GABA on the globus pallidus to inhibit its inhibitory action on the thalamic nuclei. This causes the thalamocortical pathways to become excited and signal motor neurons in the cerebral cortex to allow movement initiation, which is absent in Parkinson's disease. However, the absence of pars compact neurons has a major impact on movement, as evidenced by the symptoms of Parkinson's disease. The motor role of pars compacta may include precise motor control, as has been confirmed in animal models with lesions in this area.

Pars compacta are actively involved in reflexes to stimuli. In primates, dopaminergic neurons increase activity in the nigrostriatal pathway when a new stimulus is presented. Dopaminergic activity decreases with repeated stimulus presentation. However, the behaviorally significant presentation stimulus (i.e. reward) continues to activate dopaminergic neurons in the substantia nigra pars compacta. Dopaminergic projections from the ventral tegmental area (lower part of the "midbrain" or midbrain) to the prefrontal cortex (mesocortical pathways) and into the nucleus accumbens (mesolimbic pathway - "meso" in reference to "of the mesencephalon" ... specifically, the ventral area tires) are involved in reward, pleasure, and addictive behaviors. Pars compacta also has importance in spatial learning, observing one's environment and location in space. Lesions in the pars compacta lead to learning deficits in repeating similar movements, and some studies point to its involvement in a dorsal striate-dependent memory-based response system that functions relatively independently of the hippocampus, which is traditionally thought to promote spatial or episodic-like memory function.

Pars compacts also play a role in timing processing and are activated during playback time. Lesions in the Pars compacta result in a temporary deficit. Recently, Pars compacta has been suspected of regulating the sleep-wake cycle, consistent with symptoms such as insomnia and REM sleep disorders reported in patients with Parkinson's disease. However, partial dopamine deficiency that does not affect motor control can lead to disruption of the sleep-wake cycle, especially REM-like patterns of neural activity during wakefulness, especially in the hippocampus.

Clinical Significance

The substantia nigra is critical in the development of many diseases and syndromes, including parkinsonism and Parkinson's disease.

Parkinson's disease

Parkinson's disease is a neurodegenerative disease characterized, in part, by the death of dopaminergic neurons in the SNPC. The main symptoms of Parkinson's disease include tremor, akinesia, bradykinesia, and stiffness. Other symptoms include disturbances in posture, fatigue, sleep disturbances, and depressed mood.

The cause of dopaminergic neuron death in SNPC is unknown. However, some contributions to the specific sensitivity of dopaminergic neurons in pars compacta have been identified. On the one hand, dopaminergic neurons show abnormalities in the mitochondrial complex 1 , causing alpha-synuclein aggregation; this can lead to incorrect protein turnover and neuronal death. Secondly, dopaminergic neurons in pars compacta contain less calbindin than other dopaminergic neurons. Calbindin is a protein involved in calcium ion transport within cells, and excess calcium in cells is toxic. The Kalbindin theory explains the high cytotoxicity of Parkinson's in the substantia nigra compared to the ventral tegmentum. Regardless of the cause of neuronal death, the plasticity of Pars compacta is very reliable; Parkinson's symptoms do not appear until up to 50-80% of pars compacts of dopaminergic neurons have died. Much of this plasticity occurs at the neurochemical level; the dopamine transport systems are slowed down, allowing dopamine to linger for longer periods of time at the chemical synapses in the striatum.

Menke, Jbabdi, Miller, Matthews, and Zarya (2010) used the diffusion tensor, as well as T1 imaging, to estimate volumetric differences in SNPC and SNpr in participants with Parkinson's disease compared to healthy individuals. These researchers found that participants with Parkinson's disease consistently had less substantia nigra, specifically in SNpr. Because SNpr is connected to the posterior thalamus, ventral thalamus and, specifically, the motor cortex, and because participants with a report of Parkinson's disease having smaller SNprs (Menke, Jbabdi, Miller, Matthews, and Dawn, 2010), a small volume of this region may be responsible for the movement disorders found in patients with Parkinson's disease. This small volume may be responsible for weak and/or less controlled motor movements, which can lead to the tremors often experienced by those with Parkinson's disease.

Schizophrenia

Elevated levels of dopamine have long been implicated in the development of schizophrenia. However, much debate continues to this day around this dopamine hypothesis of schizophrenia. Despite controversy, dopamine antagonists remain the standard and successful treatment for schizophrenia. These antagonists include the first generation of (typical) antipsychotics such as butyrophenones, phenothiazines, and thioxanthenes. These drugs have largely been replaced by second generation (atypical antipsychotics) such as clozapine and paliperidone. It should be noted that, in general, these drugs do not act on dopamine-producing neurons per se, but on receptors on the postsynaptic neuron.

Other, non-pharmacological evidence in favor of the substantia nigra dopamine hypothesis includes structural changes in parse compacta, such as a decrease in synaptic terminal size. Other changes in the substantia nigra include increased expression of NMDA receptors in the substantia nigra as well as a decrease in Disbindin expression. An increase in NMDA receptors may indicate the involvement of glutamate-dopamine interactions in schizophrenia. Disbindin, which has been (controversially) associated with schizophrenia, may regulate dopamine release, and low expression of Disbindin in the substantia nigra may play an important role in the etiology of schizophrenia. Due to changes in substantia nigra in the schizophrenic brain, it may ultimately be usable special methods imaging (eg, neuromelanin-specific imaging) to detect physiological signs of schizophrenia in the substantia nigra.

Wooden chest syndrome

Shortly thereafter, MPTP was tested in animal models for its effectiveness in inducing Parkinson's disease (with success). MPTP induced akinesis, stiffness, and tremor in primates, and its neurotoxicity has been found to be very specific to the substantia nigra pars compacta. In other animals, such as rodents, Parkinson's induction of MPTP is incomplete or requires much higher and more frequent doses than in primates. Today, MPTP remains the most favored way to induce Parkinson's disease in animal models.

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Additional images

. Pars reticulata serves mainly as a transmitter (transmitter), transmitting signals from the basal ganglia to numerous other brain structures.

Represents a collection nerve cells. It is located in the dorsal part of the leg on the border with the basal part of the midbrain. Substantia nigra extends along the entire length of the brain stem from the bridge to the diencephalon. people have two Substantiae nigrae, one on each side (left and right) of the midline of the brain.

The cells of this substance are rich in one of the forms of the natural pigment melanin - neuromelanin, which gives it a characteristic dark color. In the substantia nigra, a dorsally located compact layer is distinguished ( pars compacta) and ventral ( pars reticulata) - mesh layer. Pars compacta lies more medially pars reticulata. Sometimes the third lateral layer is also mentioned - pars lateralis, although it is usually classified as part of pars reticulata. Pars reticulata and the interior of the globus pallidus are separated by an internal capsule.

Pars reticulata bears a strong resemblance, both structural and functional, to the interior of the globus pallidus. The neurons of the globus pallidum, as in pars reticulata mostly GABAergic.

The pars compacta substantia nigra consists of dopaminergic neurons. These neurons are afferent and communicate with other brain structures: the caudate nucleus and the putamen, which are part of a group called the striatum. This allows the release of dopamine in these structures.

The black substance plays an important role, thanks to it the following functions are carried out: eye movements, it regulates and coordinates small and precise movements, in particular fingers; coordinates the processes of chewing and swallowing. There is evidence of the role of the substantia nigra in the regulation of many autonomic functions: respiration, cardiac activity, and vascular tone. Electrical stimulation of the substantia nigra causes an increase in blood pressure, heart rate, and respiratory rate.

Substance nigra is an essential component of the dopaminergic reward system. She also plays a very important role in the motivation and emotional regulation of maternal behavior.

Pars reticulata substantia nigra is an important process center in the basal ganglia. GABAergic neurons in Pars reticulata transmit the final processed signals from the basal ganglia to the thalamus and quadrigemina. Besides, Pars reticulata inhibits dopaminergic activity in Pars compacta through axonal collaterals, although the functional organization of these connections remains unclear.

Most famous feature Pars compacta is - movement control, however, the role of the black substance in controlling body movements is indirect; electrical stimulation of this region of the substantia nigra does not result in body movements. Also, this nucleus is responsible for ensuring the synthesis of dopamine, which is supplied to other brain structures, through dopaminergic neurons. The function of dopamine neurons in Pars compacta black substance is complex.

The substantia nigra plays a very significant role in the development of many diseases, including Parkinson's disease. The bodies of neurons are located in the substantia nigra, the axons of which, which make up the nigrostriatal pathway, pass through the legs of the brain, the internal capsule and end in the neostriatum in the form of a wide plexus of terminal microvesicles with a high content of dopamine. It is this path that is the place in the brain, the defeat of which leads to the formation of parkinsonism syndrome.

Parkinson's disease is a neurodegenerative disease characterized by the death of dopaminergic neurons in pars compacta black substance, the cause of which is still unknown. Parkinson's disease is characterized by movement disorders: tremor, hypokinesia, muscle rigidity, postural instability, as well as autonomic and mental disorders - the result of a decrease in the inhibitory effect of the pale ball ( Globus pallidus) located in anterior section brain, striatum ( striatum). Damage to pallidum neurons leads to "inhibition of inhibition" of peripheral motor neurons (motor neurons of the spinal cord). At the moment, the disease is incurable, but the existing methods of conservative and surgical treatment can significantly improve the quality of life of patients. With the help of positron emission tomography, it has been proven that the rate of degeneration of substantia nigra neurons in Parkinson's disease is much higher than in normal aging.

An increase in dopamine levels is known to be involved in the development of schizophrenia. However, much discussion continues to this day around this theory, which is commonly known as the "dopamine theory of schizophrenia". Despite controversy, dopamine antagonists remain the standard treatment for schizophrenia. These antagonists include first-generation (typical) antipsychotics, such as butyrophenone, phenothiazine, and thioxanthene derivatives. These drugs have been largely replaced by second generation drugs (atypical antipsychotics) such as clozapine and risperidone. It should be noted that these drugs generally do not act on dopamine-producing neurons, nor on the receptors of postsynaptic neurons.

Other non-drug evidence in support of the substantia nigra dopamine hypothesis includes structural changes in the pars compacta, such as shrinkage of synaptic endings. Other changes in the substantia nigra include increased expression of NMDA receptors in the structure and decreased expression of dysbindin. Disbindin, which has been (controversially) associated with schizophrenia, may regulate dopamine release, and a measure of low dysbindin expression in substantia nigra may be important in the etiology of schizophrenia.

With the inhibition of dopaminergic transmission in the nigrostriatal system (blockade of dopamine D2 receptors) when using neuroleptics, the development of extrapyramidal side effects is associated: parkinsonism, dystonia, akathisia, tardive dyskinesia, etc.

Various independent studies have shown that many individuals with schizophrenia have an increased flow of dopamine and serotonin to postsynaptic neurons in the brain. These neurotransmitters are part of the so-called "reward system" and are produced in large quantities during positive experiences, according to the patient, such as sex, drugs, alcohol, tasty food, as well as stimulants associated with them. Neuroscience experiments have shown that even remembering positive experiences can increase dopamine levels, which is why this neurotransmitter is used by the brain to evaluate and motivate, reinforcing actions important for survival and procreation. For example, the brain of laboratory mice produced dopamine already even during the anticipation of the expected pleasure. However, some patients deliberately overexert this reward system by artificially evoking pleasant memories and thoughts over and over again, since the good mood neurotransmitters are naturally produced in this way, losing self-control in the process. This is similar to drug addiction, because almost all drugs directly or indirectly target the reward system of the brain and saturate its structures with dopamine. If the patient continues to overstimulate their reward system, then gradually the brain will adapt to the excessive flow of dopamine, producing less of the hormone and reducing the number of receptors in the reward system. As a result, the chemical effect on the brain is reduced, reducing the patient's ability to enjoy things they used to enjoy. This decrease causes the dopamine-addicted patient to increase his "mental activity" in an attempt to bring the level of neurotransmitters to a normal state for him - this effect is known in pharmacology as tolerance. Further addiction can gradually lead to very severe changes in neurons and other brain structures, and can potentially cause serious damage to brain health in the long term. Modern antipsychotic medications aim to block the functions of dopamine. But, unfortunately, this blockage sometimes also causes bouts of depression, which can exacerbate the patient's addictive behavior. Cognitive behavioral therapy (CBT), administered by a professional psychologist, can also help patients effectively control their persistent thoughts, improve self-esteem, understand the causes of depression, and explain long-term Negative consequences dopamine addiction. The "dopamine theory" of schizophrenia has become very popular in psychiatry due to the effectiveness of atypical antipsychotics that block neurotransmitters, however, many psychologists do not support this theory, considering it "simplified", there are also several different currents within the supporters of the theory.

So, when cutting the bilateral pathways from the substantia nigra to the striatum, they cause immobility in animals, refusal to eat and drink, and a lack of responses to irritation from the outside world. Damage to the substantia nigra of a person leads to voluntary movements of the head and hands when the patient sits still (Parkinson's disease), as well as many other drugs affect substantia nigra.

The substantia nigra is the main target of chemotherapy in the treatment of Parkinson's disease. Levodopa (L-DOPA), a precursor to dopamine, is the most commonly prescribed antiparkinsonian drug. Levodopa is particularly effective in the treatment of patients with early stages Parkinson's disease, although the drug does not lose its effectiveness over time. By passing through the BBB, levodopa increases the level of essential dopamine in the substantia nigra, thus alleviating the symptoms of Parkinson's disease. The disadvantage of levodopa treatment is that it eliminates the symptoms of Parkinson's disease, in which low level dopamine, and not the cause - the death of dopaminergic neurons of the substantia nigra.