Medulla oblongata – structural features, physiological role.

Lecture No. 18-20 “Functional anatomy of the brain. CHMN.”

Plan:

1. Structural organization of the brain, its physiological role.

2. Medulla oblongata – structural features, physiological role.

3. Hind brain – structural features, physiological role.

4. Midbrain – structural features, physiological role.

5. Diencephalon – structural features, physiological role.

6. FMN-area and the nature of innervation.

7. Anatomical and physiological features of the cerebral cortex.

8. Liquor formation, composition, functions.

Structural organization of the brain, its physiological role.

The brain is the main regulator of all the functions of a living organism. It is one of the elements of the central nervous system. The human brain consists of 25 billion neurons. These cells are the gray matter. Inside the brain there are cavities called ventricles. Paired cranial nerves (12 pairs) depart from it in different parts of the body.

In the course of evolution, a strong cranium has formed around the human brain, protecting this organ. The brain occupies more than 90% of the space of the skull. It consists of three main parts:

large hemispheres;

the brain stem

cerebellum.

It is also customary to distinguish five parts of the brain:

forebrain (large hemispheres);

hindbrain (cerebellum, pons Varolii);

·medulla;

the midbrain;

diencephalon.

The first section located above the spinal cord is the medulla oblongata , it is actually its continuation. The medulla oblongata is composed of gray and white matter.
Next comes the Varoliev bridge – this is a roller of nerve transverse fibers and gray matter. The main artery that feeds the brain passes through it. It starts above the medulla oblongata and passes into the cerebellum.
The cerebellum consists of two hemispheres and a vermis, as well as white matter and gray matter covering it. This department is connected by pairs of “legs” to the medulla oblongata and midbrain.
The midbrain consists of two visual hillocks, and two auditory (quadrigemina). Nerve fibers that connect the brain with the spinal cord depart from these tubercles.
The cerebral hemispheres are separated by a deep fissure with the corpus callosum inside, which connects these two sections of the brain. Each hemisphere has the following areas:

– frontal,

– temporal,

– parietal and

-occipital.

The hemispheres are covered by the cerebral cortex.
In addition, there are three layers of the brain:

hard, which is the periosteum of the inner surface of the skull; a large number of pain receptors are concentrated in this shell;

arachnoid, which is closely adjacent to the cerebral cortex, but does not line the gyrus; the space between it and the hard shell is filled with a serous fluid, and the space between it and the cerebral cortex is filled with cerebrospinal fluid;

soft, consisting of a system of blood vessels and connective tissue, in contact with the entire surface of the substance of the brain, and nourishing it.

Medulla oblongata – structural features, physiological role.

The medulla oblongata is a direct continuation of the spinal cord. Its lower border is considered to be the exit point of the roots of the I cervical spinal nerve, the upper one is the posterior edge of the bridge. The length of the medulla oblongata is about 25 mm, the shape approaches a truncated cone, the base facing up. The anterior surface is divided by the anterior median fissure, on the sides of which are elevations – pyramids formed by bundles of nerve fibers of the pyramidal pathways. These fibers partially cross (cross pyramids) in the depth of the described fissure on the border with the spinal cord. To the side of the pyramid on each side is an olive about 1.5 cm long, containing the nuclei of gray matter. The medulla oblongata is built of white and gray matter, the latter is represented by the nuclei of the IX-XII pairs of cranial nerves, olives, the reticular formation, centers of respiration and blood circulation. White matter should be distinguished from gray matter, which is formed by long and short fibers that make up the corresponding pathways.

The medulla oblongata, due to its nuclear formations and the reticular formation, is involved in the implementation of autonomic, somatic, gustatory, auditory, and vestibular reflexes. A feature of the medulla oblongata is that its nuclei, being excited sequentially, ensure the implementation of complex reflexes that require the sequential inclusion of different muscle groups, which is observed, for example, when swallowing.

The medulla oblongata regulates a number of sensory functions : skin sensitivity of the face – in the sensory nucleus of the trigeminal nerve; primary analysis of taste – in the nucleus of the glossopharyngeal nerve; auditory irritations – in the nucleus of the cochlear nerve; vestibular irritations – in the upper vestibular nucleus. At the level of the medulla oblongata, the listed sensory functions undergo a primary analysis of the strength and quality of stimulation, then the processed information is transmitted to subcortical structures to determine the biological significance of this stimulation.

It should be noted that the medulla oblongata organizes and implements a number of protective reflexes : vomiting, sneezing, coughing, tearing, closing of the eyelids. These reflexes are realized due to the fact that information about irritation of the receptors of the mucous membrane of the eye, oral cavity, larynx, nasopharynx through the sensitive branches of the trigeminal and glossopharyngeal nerves enters the nuclei of the medulla oblongata, from here comes the command to the motor nuclei of the trigeminal, vagus, facial, glossopharyngeal, accessory or hypoglossal nerves, as a result, one or another protective reflex is realized. In the same way, due to the sequential inclusion of muscle groups of the head, neck, chest and diaphragm, reflexes of eating behavior are organized: sucking, chewing, swallowing.

Excitation of the nuclei of the vagus nerve causes an increase in the contraction of the smooth muscles of the stomach, intestines, gallbladder and, at the same time, relaxation of the sphincters of these organs. At the same time, the work of the heart slows down and weakens, the lumen of the bronchi narrows. The activity of the nuclei of the vagus nerve is also manifested in increased secretion of the bronchial, gastric, intestinal glands, in the excitation of the pancreas, secretory cells of the liver.

The main centers of the medulla oblongata:

center of salivation , the parasympathetic part of which provides an increase in general secretion, and the sympathetic part – protein secretion of the salivary glands;

– the respiratory center is localized in the medial part of the reticular formation of each symmetrical half of the medulla oblongata and is divided into two parts – inhalation and exhalation.

– vasomotor center (regulation of vascular tone) – this vital center is also localized in the reticular formation of the medulla oblongata; it functions in conjunction with the overlying structures of the brain and, above all, with the hypothalamus. Excitation of the vasomotor center always changes the rhythm of breathing, the tone of the bronchi, the muscles of the intestines, the bladder, etc. This is due to the fact that the reticular formation of the medulla oblongata has synaptic connections with the hypothalamus and other centers.

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