Embryogenesis of the brain. Posterior cerebral vesicle, rhombencephalon

Phylogeny of NS. 1 type of regulation - humoral (cellular level) + endocrine. 2. Nervous regulation:

1. In coelenterates - diffuse NS.

2. In worms and other arthropods - nodal NS.

3. In lower chordates to higher vertebrates - tubular type of NS.

Embryogenesis of NS. In embryonic development nervous system stages are distinguished from the ectoderm: neural plate, neural groove and neural tube, the expanded anterior end of which is divided into three primary cerebral vesicles.

1. Rhomboid brain

2. Midbrain.

3. Forebrain.

Further transformations lead to the formation of five cerebral bubbles, the names of which correspond to the parts of the brain that are formed from them.

1. Rhomboid - additional (oblong) and posterior: bridge and cerebellum.

2. Medium

3. Front - intermediate and final.

31. General plan of the structure of the brain. Brain stem: structure of the medulla oblongata, pons, midbrain, diencephalon.

Brain are divided into sections corresponding to their origin from the cerebral vesicles: 1) the rhomboid brain, which is divided into additional (oblong), posterior and isthmus of the rhomboid brain; 2) midbrain and 3) the forebrain, including the intermediate and final.

medulla oblongata (accessory) brain(myelencephalon) is a continuation of the spinal cord, partially retaining the features of its structure; called the bulb of the brain. On the surface there are grooves and cracks similar to the formations of the spinal cord. On the anterior surface, the anterior median fissure separates roller-like thickenings - pyramids formed by motor (efferent) pathways; the transition of part of the paths to the opposite side forms a crossroads of pyramids. Lateral to the pyramid lies an oval elevation - an olive, in the depths of which lie the kernels of olives. The posterior median sulcus continues onto the posterior surface of the medulla oblongata, on the sides of which the posterior cords lie. In the upward direction, the posterior cords diverge to the sides and go to the cerebellum as part of its lower legs. Each posterior funiculus is divided by the posterior intermediate sulcus into thin and wedge-shaped bundles, composed of afferent (sensitive) pathways. The gray matter inside the medulla oblongata is represented by the switching nuclei (thin and sphenoid nuclei), the reticular formation and the nuclei of the cranial nerves (IX-XII pairs). The nuclei of the medulla oblongata carry out autonomic regulation of activity of cardio-vascular system, breathing; protective reflexes: coughing, sneezing; food reflexes: sucking, swallowing, secretion of digestive glands.

Bridge(pons) - a thickened section of the brain stem. Laterally it continues into the middle cerebellar peduncles. The dorsal surface is part of the bottom of the rhomboid fossa. Between the fibers are the nuclei of the trapezoid body. In the dorsal part of the bridge, afferent pathways pass, including the medial loop, and nuclei also lie V-VIII couples cranial nerves, reticular formation. In the ventral part, efferent pathways pass, including pyramidal and transverse fibers.

Cavity of the rhomboid brain is the IV ventricle. From top to bottom, the cavity of the IV ventricle communicates with the central canal of the spinal cord; from above, the cerebral aqueduct opens into it.

midbrain(mesencephalon) - a short section of the brain stem, forming on the ventral surface of the legs of the brain, on the dorsal surface - the quadrigemina with handles extending from the upper and lower hillocks. On the cross section: the roof and legs, the latter are divided into a tire and a base. Between the roof and the legs is the aqueduct of the brain, surrounded by a central gray matter, in which the nuclei of III-IV pairs of cranial nerves lie. In the roof of the midbrain are the nuclei of the upper (under cortical centers of the visual analyzer and through the arms of the same name are connected with the nuclei of the lateral geniculate bodies and the lower (subcortical centers of the auditory analyzer and are connected through the arms of the same name with the medial geniculate bodies) hillocks - they participate in the formation of orienting motor reactions to light and sound. In the covering of the legs of the brain are afferent pathways (medial loop), medial longitudinal beam, providing synchronous movements eyeballs, the reticular formation and the red nucleus - the coordination center of the extrapyramidal system. The base of the legs of the brain is composed of efferent pathways.

diencephalon(diencephalon) consists of two sections: the thalamic brain and hypothalamic region (hypothalamus).

thalamic brain(thalamencephalon) is divided into three main parts: the visual tubercle (thalamus opticus), the epithalamic region (epithalamus) and the foreign region (metathalamus).

Visual thalamus has an ovoid shape with a thickened posterior end (cushion). Contains numerous nuclei - subcortical centers of all types of sensitivity (except olfactory).

supra-hillous region represented by the epiphysis (upper cerebral appendage, pineal body), which is a neuroendocrine organ, and leashes. The leashes are connected by a commissure, on which the epiphysis is fixed. To foreign areas include the medial and lateral geniculate bodies, which contain nuclei - the subcortical centers of the auditory and visual analyzers.

Hypothalamus- the area lying ventral to the thalamic area in the bottom of the third ventricle. Separated from the thalamus by the subthalamic groove. It is divided into two sections: 1) the anterior hypothalamus, which includes the optic chiasm with the visual tracts, the gray tubercle, the funnel and the posterior lobe of the pituitary gland; 2) posterior hypothalamus - mastoid bodies and posterior hypothalamic region. The hypothalamus contains neurosecretory nuclei. The cavity of the diencephalon is the III ventricle - a slit-like cavity lying between the visual tubercles. The III ventricle is connected to the IV aqueduct of the brain, and with the lateral - interventricular openings.

Since this group cells arises from paired primordia and soon divides again into right and left components, it can be considered a paired structure, although due to its temporary median position dorsal to the neural tube, it has been called the ganglionic plate.

Ganglion plate grows in an anteroposterior direction. In the course of further development, its cells migrate ventro-laterally on both sides of the spinal cord and at the same time segments begin to form. Metamerically located groups of cells that arose from the ganglionic plate give rise to the ganglia of the posterior roots of the spinal nerves, and in the head region they form ganglia of the cranial nerves with sensitive components.

Primary cerebral vesicles

It was noted above conspicuous expansion of the anterior part of the neural plate. When the neural tube is formed from the neural plate, its anterior part in the region of the future brain has a larger diameter. The spinal cord is formed from the thinner part of the neural tube, located caudally from the expanded head region.

Already with his occurrence the brain shows some signs of differentiation into sections. In four-week-old human embryos, three areas of the brain can be distinguished. These are the so-called forebrain, midbrain and hindbrain. The forebrain (prosencephalon) is the widest due to the presence of eye vesicles that arise in the form of outgrowths from its lateral walls.

In the very front parts of the forebrain the complete closure of the nerve folds is somewhat slowed down. For some time there remains an opening known as the neuroporus anterior.

midbrain(mesencephalon) is separated from the anterior and somewhat less clearly from the posterior by slight narrowing of the walls of the neural tube. In early embryos, the mesencephalon exhibits little local specialization prior to the formation of specific structures.

Its roof increases in thickness and differentiates into the corpora quadrigemina (centers associated with vision and hearing), and along its bottom large fibrous crurae cerebri tracts form, which connect the more highly located suits of the brain with spinal cord.

Caudal end the hindbrain, or rhombencephalon, gradually passes into the thinner part of the neural tube, which later turns into the spinal cord. Most interesting feature last on early stages are the clear signs of neuromeric extensions that he discovers, indicating that the brain also has a metameric organization at its core.

Exact homology characteristic enlargement of the brain with specific neuromers of precancerous forms has not yet been established. The controversy revolves around the issue of neuromere fusion in the anterior part of the brain. In the brain of the embryo, at least 11 extensions can be seen, but only the more posterior of them have a characteristic appearance. Some of the anterior extensions undoubtedly represent several neuromeres. It is very possible that at least 15 neuromeres are present in the vertebrate brain.

Period, during which the brain consists of three bubbles, does not last long. By the end of the fourth week, there are already signs of impending forebrain division, and shortly thereafter differentiation of the hindbrain becomes noticeable. At the sixth week of development, we can distinguish five regions in the brain. The forebrain divided into the telencephalon telencephalon and the diencephalon diencephalon, the midbrain remained unchanged, and the hindbrain differentiated into the metencephalon anlage of the cerebellum and the anlage of the myelencephalon medulla oblongata.

telencephalon, telencephalon, is the most anterior part of the brain, and its two lateral outgrowths are called lateral telencephalic bladders. Its posterior border is easily determined by drawing a line from the fold in the roof of the brain, called the velum transversum, to the optic fossa - an depression in the bottom of the brain at the level of the optic stalks. Since this fossa lies immediately anterior to the optic chiasm, it is often referred to as the preoptic fossa.

diencephalon, diencephalon, is the more posterior part of the former forebrain. Its posterior border is conventionally defined by drawing a line from a tubercle in the bottom of the neural tube, called tuberculum posterium, to an depression in the roof of the neural tube, which already appears at this stage of development. When considering the whole embryo, it is sometimes clearly visible, and sometimes imperceptible.

most distinct diencephalon feature is the presence of lateral outgrowths that form eye bubbles, as well as a diverticulum located in the middle of the ventral wall and forming an infundibulum. An outgrowth from the middle of the dorsal wall of the diencephalon is known as the epiphysis, which, becoming noticeable in the chick embryo on the 3-4th day, appears relatively late in the pig and in man.
Usually in human embryos 9-11 mm long, there are still no signs of epiphyseal protrusion, which is first noted in 12 mm embryos.

mesencephalon midbrain in early smbryos it almost does not change. It is separated from the mesencephalon by a clearly visible constriction of the neural tube.
At this stage observed subdivision of the hindbrain of the rhombencephalon into the anlage of the cerebellum of the metencephalon and the anlage of the medulla oblongata of the myelencephalon. The dorsal wall of the neural tube immediately caudal to the meso-rhombencephalic constriction is very thick, in contrast to the thin roof of the caudal hindbrain. The part of the neural tube where this thickening is located is the metencephalon, and the end of the hindbrain with a thin roof is the myelencephalon.

Although everything external signs individual neuromeres by this time disappear, the inner surface of the myelincephalon wall reveals clear traces of metamerism.

cranial nerves

cranial nerve connections with various structures of the head and especially with the brain are very stable in all mammals. In fish we observe 10 pairs of cranial nerves. Mammals have the same 10 cranial nerves with similar relationships and functions.

Besides, brain mammals, in the process of progressive specialization, included a part of the neural tube, which in primitive fish is the unaltered spinal cord. This is evidenced by the presence in mammals of 12 pairs of cranial nerves, of which the first 10 are homologues of the 10 cranial nerves of fish, and the last two pairs represent a modification of the most anterior spinal nerves of fish.

Twelve pairs of cranial nerves identified by number and name. Starting from the most anterior, these are the following nerves: (i) olfactory (olfactorius); (II) visual (opticus); (III) oculomotor (oculomotorius); (IV) blocky (trochlearis); (V) trigeminal (trigeminus); (VI) abducens; (VII) facial (facialis); (VIII) auditory (acusticus); (IX) glossopharyngeal (glossopharyngeus); (X) wandering (vagus); (XI) additional (accessorius); (XII) sublingual (hypoglossus). In six-week-old embryos, all cranial nerves are clearly visible, with the exception of the olfactory and optic nerves.

Nerves that carry sensory (afferent) fibers, near the place of their connection with the brain have ganglia. With the exception of the auditory (VIII), all the nerves that carry the ganglia also contain a certain amount of efferent (motor) fibers, that is, they are mixed nerves. Those cranial nerves that are built almost exclusively from efferent fibers do not have external ganglia (nerves III, IV, VI, XII).

1. Name the parts of the brain at the stage of three brain bubbles.

2. In what week of intrauterine development does the brain go through the stage of five brain bubbles?

3. What parts of the brain are formed from each cerebral vesicle?

4. In what plates of the neural tube does the laying of the nuclei of "typical" cranial nerves take place?

5. What part of the fetal brain grows most intensively?

6. How is the formation of cytoarchitectonic layers of the cerebral cortex?

7. What is the relief of the hemispheres? How and when is it formed?

4.2. brain stem

1. What parts of the brain are in the brain stem?

2. Name the functions of the brain stem.

3. What cranial nerves leave the brain stem?

4. What forms the roof, tire and base of the brain stem?

5. The nuclei of which cranial nerves are located in the medulla oblongata?

6. What is the medial loop formed by and what is its functional significance?

7. What pathways pass through the tegmentum of the medulla oblongata?

8. What pathways run at the base of the medulla oblongata?

9. What centers of general importance are located in the medulla oblongata?

10. What cranial nerve nuclei are located in the pons?

11. What is the function of the fibers that make up the trapezoid body and the brain strips of the bridge.

12. What are the ascending paths in the bridge cover?

13. What is the lateral loop and how is it formed?

14. Where is the auditory pathway located?

15.Where are the native bridge cores located? Determine their function.

16. What centers are located in the upper colliculus of the quadrigemina?

17. What centers are located in the lower hillocks?

18. What cranial nerve nuclei are located in the midbrain tegmentum?

19. What are the ascending pathways in the midbrain tegmentum?

20. What descending pathways originate in the roof of the midbrain?

21. Where is the red core located and what path does it start from?

22. What pathways run at the base of the midbrain?

23. In what parts of the brain stem is the reticular formation located?

24. Determine the functions of the reticular formation of the brain.

25. Which descending paths originate from reticular nuclei? Where do they end?

Cranial nerves and areas of their innervation

1. Name 12 pairs of cranial nerves. What parts of the brain do they originate from?

2. What cranial nerves are purely sensory?

3. Why are pairs I and II not classified as typical cranial nerves?

4. Name the somatomotor cranial nerves. What nuclei do they have? What is the composition of their fibers? What do they innervate?

5. Name branchiogenic cranial nerves.

6. List the cores trigeminal nerve. What main branches does it divide into and what do these branches innervate?

7. List the cores facial nerve. What main branches does it divide into and what do they innervate?

8. List the nuclei of the glossopharyngeal nerve. What main branches does it divide into and what do they innervate?

9. List the cores vagus nerve. What main branches does it divide into and what do these branches innervate?

Cerebellum

1. Name the functions of the cerebellum.

2. What parts are distinguished in the cerebellum?

3. With what anatomical structures of the brain is the flocculent-nodular lobe of the cerebellum associated?

4. What anatomical structures of the brain are associated with the anterior lobe of the cerebellum?

5. What anatomical structures of the brain are associated with the posterior lobe of the cerebellum?

6. Describe the structure of the cerebellar cortex.

7. What fibers of the spinal cord connect the brainstem nuclei with the cerebellar cortex? In which cerebellar peduncles do they pass?

8. List the nuclei of the cerebellum. Where do the fibers from the cerebellar nuclei go? In which cerebellar peduncles do they pass?

diencephalon

1. What anatomical structures form the diencephalon?

2. What is the diencephalon cavity?

3. Name the main groups of thalamic nuclei, give their functional characteristics.

4. In what nuclei of the thalamus does the ascending pathways of superficial and deep sensitivity switch?

5. In what nuclei of the thalamus does the switching of fibers going to the cerebral cortex as part of the visual tracts take place?

6. What nuclei of the thalamus are associated with the limbic system of the brain?

7. What role does the pineal gland play in the body?

8. What centers are located in the medial geniculate bodies?

9. What centers are located in the lateral geniculate bodies?

10. Name the anatomical structures that make up the hypothalamus.

11. Name the nuclei of the hypothalamus related to middle group. What processes in the body do they control?

12. What structures of the brain is the hypothalamus associated with?

13. What is the pituitary gland and what is its functional significance?

14. What is the hypothalamic-pituitary system?

telencephalon

1. Name the anatomical structures that make up the telencephalon.

2. Name the lobes of the cerebral hemispheres. What furrows separate them?

3. Name the main convolutions and the furrows separating them in each lobe of the cerebral hemispheres.

4. Indicate where the cortical centers of the motor, musculoskeletal, auditory, visual, gustatory and olfactory analyzers are located.

5. Where are the speech centers located? Stereognosis? Praxia?

6. Where is the hippocampus located and what are its functions?

7. What is the cytoarchitecture of the cerebral cortex? What cytoarchitectonic layers is the cerebral cortex divided into?

8. What is the functional significance of cortical neural ensembles?

9. Name the basal nuclei of the telencephalon.

10. Determine the functional role of the basal ganglia.

11. What are the layers of white matter that separate the basal nuclei from each other called? What fibers pass through these layers?

Similar information.

At the next stage of brain development in embryogenesis in the anterior (rostral) at the end of the tube, three specialized swellings arise: primary cerebral vesicles - forebrain, midbrain, hindbrain (Fig. 27).

Rice. 27.

From each bubble develops one of the three main areas of the brain - the forebrain, midbrain and hindbrain. The cavities of each bladder develop into the ventricles of the brain.

Caudal part of the neural tube becomes the spinal cord. The caudal cavity of the neural tube forms the spinal canal.

Differentiation of brain vesicles

The next stage is the differentiation of the primary cerebral vesicles.

The anterior cerebral bladder is subdivided into three secondary bladders: 1) the left and right terminal bladder; 2) left and right optic vesicle; 3) an unpaired intermediate bladder (Fig. 28).

Rice. 28.

The terminal bubble undergoes the most complex changes during brain development. It develops in four directions.

The left and right bubbles begin to grow back and sideways (completely closing the intermediate bubble). The ventral-medial section of the terminal bladder merges with the lateral (lateral) surface of the intermediate bladder.

From anterior section olfactory bulbs and olfactory nerve are formed in the left and right bladder.

The cells of the walls of the terminal bladder divide and differentiate into cortical structures (cortex of the cerebral hemispheres) and subcortical structures (basal ganglia).

The neurons of the terminal bladder form axons, with the help of which they establish connections with other parts of the nervous system. These axons assemble into bundles that form three major white matter systems: white matter of the cerebral cortex, corpus callosum (corpus callosum), external capsule.

White matter of the cerebral cortex contains axons that connect neurons within the cerebral cortex of one hemisphere. corpus callosum contains axons that connect cortical neurons located in different hemispheres. External capsule contains axons connecting the cerebral cortex with the brain stem, in particular, with the thalamus.

The inner space of the terminal bladder forms the lateral ventricles of the brain.

Thus, the cerebral hemispheres (telencephalon) develop from the terminal bladder, which include the cerebral cortex, subcortical nuclei, olfactory brain, white matter, and lateral ventricles of the brain.

From intermediate bubble develop thalamus and hypothalamus. The inner space of the intermediate bladder forms the third ventricle of the brain.

From visual bubble develop optic nerve and retina. Thus, the retina and optic nerve are part of the brain, not the peripheral nervous system.

Medium bubble undergoes minor changes compared to the anterior bladder. The dorsal side of the middle bladder develops into a hectum or quadrigemina. The ventral side of the middle bladder develops into the tegmentum (Fig. 29). The narrow internal space filled with cerebrospinal fluid turns into cerebral aqueduct, which connects the third and fourth cerebral ventricles.

Rice. 29.

rear bubble develops into three structures: 1) cerebellum; 2) Varoliev bridge; 3) medulla oblongata (Fig. 30). The cerebellum and the pons Varolii are formed from the rostral posterior bladder. From the diamond-shaped lips, which are located on the dorsal side of the posterior bladder, the cerebellum is formed. The lips grow dorsally and medially, then unite into a single whole. The ventral wall of the posterior bladder forms the pons Varolii. The medulla oblongata is formed from the caudal part of the posterior bladder. The ventral and lateral sides of the bladder expand, and the dorsal side turns into a thin roof consisting of ependymal cells. White matter forms on the ventral side of the medulla oblongata (pyramids of the medulla oblongata).

Rice. 30. Diffraction of the posterior bladder: a - development of the rostral posterior bladder; b- development of the caudal posterior bladder

On fig. 30 shows the development of the posterior bladder. The inner space of the posterior bladder, filled with cerebrospinal fluid, turns into the fourth cerebral ventricle (Fig. 31).

Rice. 31.

On fig. 31 shows the development of the spinal cord.

Development of the cerebral hemispheres

The surface of the cerebral cortex during ontogenesis grows strongly, forming numerous folds (furrows and convolutions). The main stages in the development of the cerebral cortex are shown in fig. 32-33.

Rice. 32.

Rice. 33.

development

The cerebral cortex differentiates into four large lobes: 1) frontal; 2) parietal; 3) temporal; 4) occipital (see Fig. 33).