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  3. Departments of the central nervous system

Departments of the central nervous system

Anatomical and functional nervous system is divided into somatic and autonomic. The somatic nervous system provides a voluntary and involuntary movements of the skeletal muscles. The central part of the somatic nervous system includes the brain and spinal cord. The autonomic nervous system controls the operation of the internal organs, regulates metabolism.

The basis of the nervous system – the brain and spinal cord, from the developing neural tube. The average weight of the brain of an adult human is about 1.5 kg, and although there is considerable variation. For example, brain Turgenev had a mass of 2.0 kg, and the brain of Anatole France – only 1.2 kg, which, however, does not affect the intelligence of famous writers. In the brain of a young man, there are about 10 billion neurons and 90 billion glial cells. The brain needs a continuous supply of oxygen and glucose it. A break in the blood supply to the brain by a fraction of a minute leads to loss of consciousness, and in 5 minutes – to irreversible changes and death. From about the age of 30 a person begins the process of the withering away of neurons, and one day dies to one thousand neurons so that the brain is the 100th person contains about two-thirds of the number of neurons of 18-year-old boys. In smokers, alcoholics, drug addicts, and especially the processes of degradation of the brain begins sooner, and their rate is much higher than that of a healthy person. In the brain, there are no pain receptors, so headaches discomfort associated with irritation of receptors of the meninges, neck muscles, eyes, scalp.

The spinal cord is located in the spinal canal and a strand length of 43-45 cm and weighing about ’30 top of the spinal cord enters the lower part of the brain – the medulla oblongata, and the bottom ends at the level of the lumbar vertebrae. The spinal cord is washed cerebrospinal fluid – liquor. Two – front and back – longitudinal grooves spinal cord is divided into two symmetrical halves. A cross section clearly shows that in the center of the spinal cord around the spinal canal are bodies of neurons that make up the gray matter of the spinal cord. Arranged around the gray matter of the processes of the nerve cells of the spinal cord, as well as coming into the spinal cord axons of neurons in the brain and peripheral ganglia, which form the white matter of the spinal cord. A cross section of gray matter like a butterfly, and it distinguishes the front, rear and side horn. The anterior horns are motor neurons (motor neurons), whose axons of the excitation reaches the skeletal muscles of the limbs and trunk, causing them to shrink. The rear horns are mostly body neurons linking processes sensory neurons with the bodies of motor neurons and transmit information to other parts of the central nervous system. The lateral horns of gray matter are bodies of neurons sympathetic nervous system.

The spinal cord is divided into segments, each of which extend a pair of mixed (i.e. containing efferent and afferent fibers) spinal nerves. Total number of such pairs 31. Each of the two roots of nerves begins: front – motor – and back – sensitive. As part of the spine from the front lateral horn neurons also depart fibers to the sympathetic ganglia of the autonomic nervous system. In the dorsal root of the spinal cord are located thickening – ganglia (ganglion) in the body which are sensitive neurons in the spinal cord carry information mainly of the limbs, trunk and the skin. Into the holes between the vertebrae anterior and posterior roots join to form a single mixed spinal nerve.

Each segment of the spinal cord innervate certain part of the human body. So, from the cervical and upper thoracic spinal cord segments depart the nerves to the muscles of the neck, upper limbs and organs located in the chest cavity. The lower thoracic and upper lumbar segments innervate the muscles of the trunk and abdominal organs. The lower lumbar and sacral segments control the operation of the muscles of the lower limbs and organs located in the pelvis.

The spinal cord has two functions: conducting and reflex. The conductive feature is that the fibers of the white matter information from the cutaneous receptors (touch, pain, temperature), receptors of the limbs and trunk, receptor vessels, the urogenital system enters the brain. Conversely, from the motor centers of the brain receives impulses to anterior horn motoneurons, and when they are excited – to the muscles of the limbs, trunk, and so on. D.
Reflex functions of the spinal cord is that his motor neurons (motor neurons) controlling the movements of the limbs, trunk and part of the neck. Autonomic centers of the spinal cord are involved in the regulation of cardiovascular, respiratory, digestive, excretory, reproductive systems.

It should also indicate that the information coming from the peripheral systems to the brain through the spinal cord, the latter is subjected to a partial analysis and processing. For example, the spinal cord can influence the effect of pain.
All the reflexes of the spinal cord are under the control of a powerful brain. Thus, in case of injuries, leading to rupture of the spinal cord below the break restored only simple flexor reflexes, such as the knee, and that violations.
The brain is divided into five sections: the medulla oblongata, midbrain, cerebellum, midbrain and the cerebral hemispheres. Medulla oblongata is a natural extension of the spinal cord, but the segmentation he is weaker, and the neural organization is more complex than in the spinal cord.

Medulla performs conductive and reflex functions. Through it pass all the paths that connect the neurons of the spinal cord to higher brain centers. Phylogenetically oldest brain is a thickening of the anterior end of the neural tube, and there are many important centers for human life reflexes. So, in the medulla oblongata is the respiratory center neurons are divided into inspiratory (inhalation) and expiratory (exhalation). In response to increasing levels of carbon dioxide in the blood, inspiratory neurons are excited by sending pulses to the spinal motoneurons; from them impulses go to the intercostal muscles and the diaphragm, causing them to shrink. There is a breath. Here in the medulla oblongata is vasomotor center. Its neurons are constantly discharging nerve impulses, maintain an optimal lumen of blood vessels, allowing normal blood pressure. Artificial stimulation of neurons front of the center leads to a narrowing of blood vessels, raising the pressure, heart palpitations. Irritation neurons rear of the center leads to the opposite effect. Descending neural pathways of neurons that end in the center of the preganglionic neurons of the sympathetic nervous system, located in the lateral horns of gray matter of the thoracic spinal cord segments.

Medulla – the place of entry and exit of twelve pairs of cranial nerves. Some of these nerves is a motor (efferent) and innervates primarily the muscles of the neck and head, and some – sensitive (afferent), t. E. The brain carries information from different senses. The nuclei – clusters of bodies of neurons – IV pairs of cranial nerves are located in the overlying parts of the brain, and they just go through the medulla oblongata to the exit from the skull, and the core VI-XII pairs are located either directly in the medulla oblongata, or on its border with the average brain.

In the central part of the medulla oblongata begins reticular formation of the brain stem – the accumulation of a vast number of seemingly randomly distributed neurons. The neurons of the reticular formation have strong ties with the structures of the forebrain – the thalamus, hypothalamus, limbic system, cerebral cortex. Sending pulses into the overlying structures, neurons of the reticular formation of the forebrain is maintained in the waking state. The defeat of the area leads to drowsiness, loss of consciousness, lethargic sleep. Downward path from the reticular formation ending in motor neurons of the anterior horns of the spinal cord, by participating in the maintenance of body posture, coordination of movement.

The cerebellum is located on the rear side of the barrel behind the elongated and middle parts of the brain. The average weight of an adult human cerebellum – 150 g To what extent the structure of the cerebellum follows the structure of the brain. With an average brain cerebellum is connected to three pairs of legs. It consists of a worm (stem, the most ancient part), and the hemispheres separated by furrows into shares. The shares are divided into small grooves gyrus. Cerebellar hemispheres are covered with three-layer cortex, most neurons in the cortex – the brake. Their task – to slow worm neurons, preventing the circulation of long pulses of motor neuron circuits. The cerebellum receives information from all propulsion systems: a department of the cerebral hemispheres, from the middle of the brain, the spinal cord. The main functions of the cerebellum are: 1) the regulation of body posture and maintaining muscle tone; 2) coordination of voluntary movements with slow posture of the whole body; 3) ensuring the accuracy of rapid voluntary movements.

With the destruction of the worm a person can not walk or stand, disturbed sense of balance. When the affected hemisphere of the cerebellum, a decrease in muscle tone, severe trembling limbs, impaired accuracy and speed of voluntary movements, fatigue. Disturbed as speech and writing.
Midbrain as long, is part of the brain stem. On the surface of it, facing the cerebellum, there are 4 small hump – quadrigeminal bodies. Superior colliculus – centers of primary processing of visual information, their neurons respond to objects moving quickly into view. The main functions of the neurons of the upper mounds – control the direction of view and bringing the visual system on high alert for strong visual stimulus.

Lower colliculus – centers of primary processing of auditory stimuli. Neurons in these centers to respond to the strong, harsh sounds, the auditory system resulting in a state of high alert.
In the midbrain are the most important clusters of neurons that perform motor functions – red nucleus and substantia nigra. The neurons of the red nucleus, together with the neurons of the cerebellum are involved in maintaining muscle tone and coordination body posture. With the destruction of the red nucleus pathologically increased tone of the extensor muscles of the limbs. The neurons of the substantia nigra contain a mediator of dopamine and axons of these neurons are in the forebrain structures. When people want to make any voluntary movement, then in a few hundredths of a second before the movement excited neurons of the substantia nigra. In severe disease, Parkinson’s disease substantia nigra neurons cease to produce dopamine and are destroyed. Thus the person loses the ability to start voluntary movement, is inhibited, and also suffers emotional sphere may develop dementia.

In the center are arranged midbrain raphe nucleus neurons which contain as neurotransmitter serotonin. Serotonin is one of the most important factors causing sleep. If these core experimentally disrupted, the animals lose their ability to sleep. On average, the brain continues to brain stem reticular formation, as described earlier.

Diencephalon consists of the thalamus, the hypothalamus (hypothalamic region) and nadbugrovoy area, which includes endocrine gland pineal gland. Down from the hypothalamus is located on a thin stalk pituitary endocrine gland.
The thalamus is the center of the analysis of all kinds of sensations, except the olfactory. Despite its small size – about 19 cm3 in the thalamus there are more than 40 pairs of nuclei (clusters of neurons) with a variety of functions. Specific core analyzed different types of sensations and convey information about them to the appropriate areas of the cerebral cortex. Thus, the lateral geniculate body – visual information analysis centers, medial geniculate body – auditory information analysis centers, ventrobasal core – the center of analysis of the information coming from the receptors of muscles, skin, and so on. D.
Non-specific thalamic nuclei (eg, medial) are a continuation of the reticular formation of the brain and the structures required for the activation of the forebrain. Motor nucleus (for example, ventrolateral) are involved in the coordination of motor systems in the brain. Associative core (eg dorsomedial) are needed for comparison and summation of various kinds of sensations and create a complete image of the object. Ventral nucleus of the thalamus are higher centers of pain sensitivity, it is here that the painful sensation. These nuclei may be linked so-called phantom pain, where the pain is felt, for example, long amputated limb. The pain is the result of abnormal excitation of the neurons in the ventral nuclei that were once associated with the long absence of limbs. Patients with disrupted ventral nuclei often violated all sense of time. Apparently, in these nuclei are neurons that act as “internal clock” of the body.

The lower part of the intermediate brain – the hypothalamus – also serves an important function as the highest center of the autonomic regulation. The front of the nucleus of the hypothalamus – the center of parasympathetic effects, and the rear – sympathetic. The medial portion of the hypothalamus – the main body of neuroendocrine neurons that secrete into the blood area are a number of controls that affect the activity of the anterior pituitary. Furthermore, in this area the most important hormones are synthesized oxytocin and vasopressin (antidiuretic). In these nuclei are synthesized, many physiologically active peptides, affecting all aspects of life of the body: the perception of information, emotions, internal organs, and so on. N.
In the hypothalamus are centers of hunger and thirst, irritation of neurons that leads to the indomitable absorption of food or water.

Thus, we can say that the hypothalamus is required to ensure vegetative accompaniment voluntary and involuntary somatic human activity. Hypothalamic lesions accompanied by severe endocrine and autonomic disorders: decreased or increased pressure, deceleration or rapid heart rate, shortness of breath, impaired intestinal motility, thermoregulation disorders, changes in blood composition, and so on. D.

In the interior of the white matter of the cerebral hemispheres of the brain is a complex brain subcortical nuclei, called the limbic system. By the limbic structures include hippocampus, amygdala, septum. The limbic system is a major emotional center of the brain, providing the emotional evaluation of the situation, assess the possible consequences of this situation and the choice of one of the alternative forms of behavior. As a result, the correct choice of the behavior of the body must come into compliance with their needs – for example, avoiding danger, or to provide themselves with food, and so on. D.
Hippocampus in origin is an ancient bark. Its function – participation in the evaluation and imprinting new information, ie memorizing and learning. People with destroyed hippocampus memorization of new information difficult. Amygdala nuclei lies in the depth of the temporal lobes, and is closely connected to the hypothalamus. In this region there are clusters of neurons, which leads to irritation of the unbridled rage, panic and fear. Also found the pleasure centers, which upon stimulation of the body begins to produce substances similar to morphine. The destruction of the amygdala leads to a reduction of emotion, lack of fear and anxiety, dementia, risibility, apathy.

At the base of the cerebral hemispheres are the basal ganglia – the large kernel provides a link between motor areas of the cerebral cortex and other motor centers of the brain (midbrain, cerebellum, and others.). The basal ganglia axons terminate in neurons located in the substantia nigra of the midbrain. The most important function of the basal ganglia – remembering complex motor programs: walking, running, dance moves, exercises and sports t. D.
Phylogenetically the youngest formation of the brain is the cerebral cortex. This layer of the gray matter (i.e., bodies of neurons) covering the entire forebrain.