The anatomical features of nervous system in children

Размещено на http://www.allbest.ru/

Размещено на http://www.allbest.ru/

Kazakh National Medical University named after S.D. Asfendiyarov

Normal anatomy

Theme: The anatomical features of nervous system in children

Done: Belyavskaya D.I., 3 cource, GM faculty, 48-1 group

Almaty, 2015

The nervous system of the children, on the one hand, is very similar to the structural organization of the nervous system in adults. On the other hand, when child has been born such structures as brain and spinal cord are not fully formed,they are not sufficiently mature physiologically and anatomically. This determines the particular originality of motor, sensory, and psychological and emotional life of the child. The progressive development of the nervous system is going on till 20-25 years.

Differences in cognition, behavior, and emotions between children, adolescents, and adults have been noted for millennia. Characterizing the neuroanatomical substrates of these differences has been more elusive. Data from animal and post-mortem studies has been able to tell us much about the basic processes underlying the development of the brain, but these types of studies are limited in what they can tell us about how individuals change over time, the extent of variability between individuals, what factors may impact that change, and the functional correlates of these differences.

Key events in brain development.

The development of the nervous system occurs through the interaction of several synchronized processes, some of which are complete before birth, while others continue into adulthood. The first key event in the development of the central nervous system is the formation of a specialized fold of ectodermal tissue called the neural tube (Picture 1 a,b,c) (Picture 4).

In early development, there are only three bulges, or vesicles, in the neural tube. As an embryo develops, these vesicles begin to differentiate into subdivisions which are commonly called the forebrain, midbrain, and hindbrain.

We humans share these developmental differentiations in the brain with all other vertebrates including bony fish, amphibians, reptiles, birds, and of course, other mammals.

Picture 1.(a) first step of In early development, there are only three neural tube orfanization. bulges, or vesicles, in the neural tube.

As an embryo develops, these vesicles/brain-development-embryos.html begin to differentiate into subdivisions which are commonly called the forebrain, midbrain, and hindbrain. We humans share these developmental differentiations in the brain with all other vertebrates including bony fish, amphibians, reptiles, birds, and of course, other mammals.

Lautin points out that because everything is initially positioned in the mid-line, the lateral ventricles, an internal cavity in both the left and right cerebral hemispheres, have to be lateral evaginations wherein the neural tube turns outward. In the illustration below, you can see how these prosencephalon evaginations begin to take shape to produce the telencephalon (which develops into the left and right cerebral hemispheres and ventricles) and diencephalon (which develops primarily into the thalamus and in neural tube orfanization.

Picture 1.(b) second step hypothalamus).

Lautin explains that the telencephalon is the "most forward projected ventricle," sort of an "end-brain." The prefix tele, from the ancient Greek, means "at a distance" or "end." Given the use of the prefix di, Lautin explains that the diencephalon is a "between brain" or "inter-brain."

While the mesencephalon remains relatively undifferentiated, the rhombencephalon will also develop into two vesicles--the metencephalon (further develops into the pons and cerebellum) and the Picture 1.(c) neural tube myelencephalon (develops into the medulla organization-final oblongata). Source:

Picture 1.(c) neural tube organization-final

The neural tube nears by 3-4 weeks of gestation (Picture 2) /brain-development-embryos.html and is the basis for all further nervous system development. Birth defects such as spina bifida and meningomyelocele arise from abnormalities in neural tube formation (Victor et al., 2001).

From 4 to 12 weeks the neural tube differentiates into what will become various components of the nervous system.

The forebrain and facial structures develop at one end, and the spinal cord at the other.

Picture 2. Sequence of events in brain maturation.

The hollow center of the tube in the region that will become brain will eventually form the ventricles. Regions called proliferative zones form near the ventricles and give rise to young neurons.

From 12 weeks to 20 weeks these neurons multiply and migrate from their origins to destinations in the cortex, moving along a scaffolding of glial cells (Rakic, 1990). After this migration, a period of rapid cell death occurs, reducing the neural number by half from 24 weeks of gestation to 4 weeks after birth. The cell bodies of the neurons are primarily found in the gray matter of the brain. Their myelinated axons form white matter. Myelination occurs regionally beginning with the brain stem at 29 weeks (Inder and Huppi, 2000) and generally proceeds from inferior to superior and posterior to anterior. Proximal pathways tend to myelinate before distal, sensory before motor, and projection before association (Volpe, 2000). Although most major tracts are significantly myelinated by early childhood, axons within the cortex and in some regions such as the arcuate fasciculus, a white matter bundle near the temporal lobe, continue to myelinate into the second and third decades of life (Yakovlev and Lecours, 1967). A third major developmental process is the proliferation and organization of synapses, which begins slightly later, around the 20th week of gestation. Synaptic density increases rapidly after birth, reaching by 2-years of age a level approximately 50% greater than that typically seen in adults (Huttenlocher, 1979).

This is followed by a regionally specific loss of synaptic connections. For example, maximum synaptic density occurs in the visual cortex at 4 months postnatally, but it does not typically peak in the prefrontal cortex until 4 years of age. Beginning at approximately 15 weeks the surface of the growing brain begins to fold into sulci and gyri (Levine and Barnes, 1999) (picture 3)

The major sulci, except for the occipital lobe, are in place by 28 weeks of gestation, after which secondary and tertiary sulci are elaborated, with nearly all gyri present by birth. The sulcal and gyral patterns continue to increase in complexity after birth, likely related to changes in cellpacking density and maturation of subcortical tracts.

Picture 3. Embryo.

The dynamic interplay between progressive and regressive events results in relatively rapid brain growth in the first 2 years of life, by which time it has achieved 80% of its adult weight. By age 5 years brain size is approximately 90% of adult size (Dekaban and Sadowsky, 1978).

Picture 4.Graph. The formation of a tube from the flat layer of ectodermal cells known as the neural plate. This will give rise to the central nervous system.

Another classification concerns trimester of pregnancy stages:

In the first trimester of pregnancy is such stages of development of the nervous system of the fetus (picture 5):

Picture 5: The main events in the development of the CNS and motor development during the first 8 weeks of pregnancy

1) The dorsal induction or primary neurulation (Picture 6)

- the period of 3-4 weeks of gestation;

2) Ventral induction - a period of 5-6 weeks of gestation;

3) Partial neuronal proliferation - a period of 2-4 months of gestation;

Picture 6. primary neurulation

Dorsal induction or primary neurulation - in connection with the development of individual characteristics may vary over time, but always adheres to 3-4 weeks (18-27 days after conception) of gestation. During this period, the formation of the neural plate, which after closing its edges transforms into the neural tube (4-7 weeks of gestation).

Ventral induction - this stage of the formation of the nervous system of the fetus reaches its peak at 5-6 weeks of gestation.

During this period the neural tube 3 appear dilated cavity (at the front end thereof) of which are formed after:

· from the 1st (cranial cavity) - the brain;

· of the 2nd and 3rd cavity - the spinal cord.

· Due to the division into three bladder, nervous system develops further and the germ of the fetal brain of the three bubble turns into a five-way division.

· From the front of the brain is formed - the ultimate brain and midbrain.

· From the posterior cerebral bubble - laying the cerebellum and medulla. (Picture 7)

· In the first trimester of pregnancy is also being partially neuronal proliferation.

· The spinal cord develops faster than the brain, and therefore starts to function as quickly, making plays an increasingly important role in the early stages of fetal development.

Picture 7. Brain development at embryo.

But in the first trimester of pregnancy deserves special attention to the development of the vestibular analyzer (picture 8). It is a highly specialized analyzer, which is responsible for the perception of the fetus moving in space and the feeling of change of position. This analyzer is formed already in the 7th week of fetal development (before other analyzers!), And to the 12-th week to have him fit nerve fibers. Myelination of nerve fibers begins with the appearance of the first movements of the fetus - 14 - week gestation. But for impulses from the vestibular nuclei to the motor cells of the anterior horn of the spinal cord need to be myelinated vestibular - spinal tract. His myelination occurs in 1-2 weeks (15 - 16 weeks of gestation).

Therefore, due to the early formation of vestibular reflexes, moving the pregnant woman's fetus moves in the space in the uterus. At the same time, the movement of the fetus in the space is "annoying" factor in the vestibular receptor that sends impulses for the /brain-development-embryos.html the further development of the nervous system of the fetus.

Violations of the fetus from the effects of different factors in this period leads to violations of the vestibular apparatus in the newborn child.

Until the 2nd month of gestation fetus has a smooth surface of the brain covered ependymal layer consisting of medulloblastomas. By the 2 - th month of fetal development begins to form the cortex by migrating neuroblasts in in overlying boundary layer, and thus forming a tab of the gray matter of the brain.

All adverse impacts in the first trimester of fetal development of the nervous system can lead to severe, in most cases, irreversible damage of the operation and the further formation of the nervous system of the fetus

The second trimester of pregnancy. (picture 8)

Picture 8: The main events in the development of the CNS and motor development during second trimester

Neuronal proliferation is the main process of ontogenesis.

At this stage of development there is a physiological brain edema bubbles. This is due to the fact that the cerebrospinal fluid entering the brain bubbles expands them.

By the end of the 5th month of gestation produced all the major groove of the brain, and there are holes Lyushka through which cerebrospinal fluid enters the outer surface of the brain and washes it.

Within 4 - 5 months of intensive development of the brain cerebellum. He acquires a characteristic he tortuosity, and share across, forming its main parts: the front, rear and follicle-nodular share.

Also in the second trimester of pregnancy through Unit cell migration (5 months), in which there is zoning. The brain of the fetus becomes more similar to the brain of the adult child.

Under the influence of negative factors on the fetus during the second period of pregnancy, there are disorders that are compatible with life as a bookmark nervous system took place in the first trimester. At this stage, violations connected with hypoplasia of the brain structures.

Your provider will measure the height of your uterus (the fundal height). This measurement is taken from the top of your pubic symphysis (pelvic bone) to the top of your uterus. From 20 weeks until 35 weeks there is generally a relationship between the fundal height and the length of your pregnancy. For example, fundal height should be 20 centimeters (+ or - 2 cm) at 20 weeks, 30 centimeters (+ or - 2 cm) at 30 weeks, etc. Sometimes, however, this measurement is not accurate; fundal height may be unreliable in women who are obese, who have fibroids, who are carrying more than one fetus, or who have excess amniotic fluid.

Your provider will use the increase in your uterine size as a marker for fetal growth. There is normal variance among the actual measurements, and a 2 or 3 cm difference is not generally a cause for concern. If your fundal height does not grow or is growing slower or faster than expected, your provider will probably order an ultrasound to evaluate the fetus and the amniotic fluid.

Third trimester of pregnancy. (picture 9)

Picture 9: The main events in the development of the CNS and the motor development during third trimester

During this period, the organization and myelination of brain structures. Sulci and gyri in its development approach to the final stage (7 - 8 months of gestation).

By stage of the organization of neural structures to understand the morphological differentiation and the emergence of specific neurons. In connection with the development of cell cytoplasm and increase of intracellular organelles is increased formation of metabolites that are essential for the development of neural structures: proteins, enzymes, glycolipids, mediators, etc. In parallel with these processes occurs formation of axons and dendrites for synoptic contacts between neurons.

Myelination of nerve structures begins with 4-5 months of gestation and ends at the end of the first, the beginning of the second year of life, when the child begins to walk.

Under the influence of adverse factors in the third trimester of pregnancy and during the first year of life, when ends the process of myelination of the pyramidal tract, there is no serious violations. The ability to easily change the structure, which are determined only by histological examination.

The development of the CSF and the circulatory system of the brain and spinal cord.

In the first trimester of pregnancy (1 - 2 months of gestation), when the formation of the five brain vesicles, the formation of the vascular plexus in the cavity of the first, second and fifth cerebral bubble. These plexus begin to secrete highly concentrated liquor, which is, in fact, the nutrient medium due to its high content of the protein and glycogen (greater than 20 times, unlike adults). CSF - in this period is the major source of nutrients for the development of nervous system structure.

Until the development of the brain structures supports liquor at 3 - 4 week gestation formed first vessels of the circulatory system, which are located in a soft-arachnoid. Initially, the oxygen content in the arteries is very low, but within 1 - 2 nd - th month of intrauterine development of the circulatory system becomes more mature look. And in the second month of gestation blood vessels begin to grow into the medulla to form a network of blood.

By 5 - th month of neural development appear anterior, middle and posterior cerebral arteries, which are interconnected by anastomoses, and represents the completion of the structure of the brain.

Blood supply to the spinal cord is due to more sources than the brain. Blood is supplied to the spinal cord from the two vertebral arteries which branch into three arterial tract, which in turn, extend along the entire spinal cord, feeding it. Anterior horn receive more nutrients.

Venous system prevents the formation of collateral vessels is more isolated, which contributes to the rapid removal of the end products of metabolism through the main veins on the surface of the spinal cord and bred in spinal venous plexus.

A feature of the blood supply to the third, fourth and lateral ventricles in the fetus is a wider dimension of the capillaries that take place in these structures. This results in impaired blood flow, which promotes more intensive nutrition.

Immature blood brain barrier- Children have immature blood-brain barriers and enhanced central nervous system (CNS) receptivity. As a result, children may exhibit a prevalence of neurological symptoms. Nerve agents may produce more symptoms in pediatric patients, requiring levels of treatment for children that are not indicated for adults with the same level of exposure.

To summ up, threre some main anatomical features of CNS in children:

The brains of children.

The brain grows rapidly during the period before birth and then slows considerably during the per-school years. At birth the brain is typically 25% of its adult size.

Importantly, about half of the postnatal growth of the brain volume occurs during the first year of life, and attains about 75% of its adult size by the end of the second year.

Neonatal brain relative magnitude greater than in adults: its weight is about 1/8 of the body weight (average 400 g), whereas in adults - 1/40 body weight. Large gyrus and sulcus is already well defined, although they have less depth and height. Small fissures and convolutions (tertiary) a little, they gradually formed during the first years of life. The cells of the gray matter, the conductive system (pyramidal path, etc.) Are not fully formed dendrites short malorazvetvlёnnye. As the sulci and gyri (increasing their number, it changes the shape and topography) occurs formation and myelo cytoarchitectonics different parts of the brain. Particularly intensive, this process occurs in the first 6 years of life.

Anatomically, the brain structures mature adult only to the level of 20 years.(picture 10)

It is believed that the number of nerve cells of the cerebral hemispheres after birth does not increase, and are only their differentiatio and increase in size and volume.

Picture 10. Anatomy of the inside of the brain. Source:

The maturation of cells of the medulla oblongata ends mainly to 7 years. Later, all in puberty ends differentiation of cellular elements of the gray matter of the hypothalamic region. (Picture 11)

Picture 11. Ratio of GM&WM

The nervous system in children. Meninges (picture 12,13).

Subcortical motor analyzer, integrating the activities of the extrapyramidal system, formed by the birth. However, movements of the newborn are chaotic, unfocused have atetozopodobny character dominates the tone myshtssgibateley. This level of organization of movements called piramidnostriarnym. Cerebellum, and striatum still underdeveloped. Coordination of movements begins to develop gradually after birth. First, it concerns the eye muscles, which is manifested in the child 2-3y week of life on fixing gaze on a bright object. Then the child begins to follow a moving toy, turning his head, indicating that the initial coordination of the neck muscles.

Dura in neonates is relatively thin, adherent to the bones of the skull base to a considerable extent. Soft, rich in blood vessels and cells of the brain and the arachnoid membrane is very thin. Subarachnoid space formed by these sheets is insignificant volume.

Highly vascular piamater. Children illustrate highly vascular piamater, there is subarachnoid space in places where the blood-brain barrier is vulnerable--such as the choroid plexus, concerns the fact that children have immature blood-brain barriers and enhanced central nervous system (CNS) receptivity.

Picture 12: cranial meninges scheme.

Picture 13: spinal meninges scheme.

CSF (cerebrospinal fluid): The CSF space is a dynamic pressure system. CSF pressure determines intracranial pressure with physiological values ranging between 3 and 4 mmHg before the age of one year, and between 10 and 15 mmHg in adults. Newborns have a narrow subarachnoid space (6-8 mm) and low CSF pressure, and higher total CSF (neonates 10 ml/kg, infants and toddlers 4 ml/kg, adults 2 ml/kg) and spinal CSF volumes (50% in children vs. 33% in adults).

Anatomical localization of CSF (cerebrospinal fluid) can be illustrated through the a lumbar puncture procedure that is usually performed to look for evidence of meningitis or other nervous system disorders (picture 14)

Also, increased fluid pressure typically leads to compression of the surrounding neural tissue, which then leads to increased fluid volume. Since the bones of the skull are not fused in a developing fetus or newborn infant, increased fluid pressure in the brain may cause the head to grow to an abnormally large size (see Hydrocephalus ), called macrocephaly. The skull bones are fused after about 2 years of age, so increased fluid pressure and volume after that point will most likely result in compression of, and damage to, neural tissue.

The spinal cord in children.

The spinal cord in newborns compared with the head is morphologically more mature education. It determines its more advanced features and the presence of spinal automatism at the time of birth.

By the end of 2-3 years of myelination of the spinal cord and the spinal cord, forming a "ponytail". The spinal cord is slowly growing in length of the spine. In newborn it terminates at the level Lm, whereas an adult - at the upper edge L ". The final ratio of the spinal cord and spinal column is set to 5-6 years.

Picture 14 : Cross section of spinal cord with indicating CSF location

By the end of 2-3 years of myelination of the spinal cord and the spinal cord, forming a "ponytail". The spinal cord is slowly growing in length of the spine. In newborn it terminates at the level Lm, whereas an adult - at the upper edge L ". The final ratio of the spinal cord and spinal column is set to 5-6 years.

Dural Sac: Age-related anatomic variations exist in the location of the caudal termination of the dural sac. During early development in utero, the spinal cord exists throughout the entire spinal canal. Differential growth of the vertebrae compared to the nerves and cord account for a relative ascension of the cord within the canal over time. Terminates at S 3 and spinal cord at L 3 vertebral levels, at birth. Adult level (S 2 and L 1 respectively) is not reached until 2 nd year of life. (picture 15)

The nervous system in children. Myelination of nerve fibers in children.

An important indicator of maturation of neural structures - myelination of nerve fibers. It develops in a centrifugal direction from the cells to the periphery. Philo and developmentally older systems myelinating before. Thus, myelination in the spinal cord begins at the 4th month of fetal development, and it is almost newborn ends. In this first myelinating motor fibers, and then - sensitive. In different parts of the nervous system myelination occurs simultaneously. First myelinating fibers performing vital functions (sucking, swallowing, breathing, etc.).

Picture 15: Anatomical differences between pediatric and adult spinal cord

Cranial nerve myelinating more active during the first 3-4 months of life. Their myelination is completed in about a year of life, with the exception of the vagus nerve. The axons of pyramidal pathway myelin covered mainly by 5-6 months of life, finally - to 4 years, which leads to a gradual increase in range of motion and accuracy. Also, it should be mentioned that in children, endoneurium is loose.

Spine and Ligaments: Ligaments are less densely packed, and feel of loss of resistance is less marked. Increased spine flexibility limits normal thoracic kyphosis and facilitates cephalad spread and higher level of sensory block. Laminae are cartilaginous; hence, paramedian approach should be avoided.

The nervous system in children. The development of conditioned reflex activity in children.

One of the main criteria for the normal development of the brain of the newborn - the main condition the unconditioned reflexes, since they formed the basis of conditioned reflexes. The cerebral cortex, even in the newborn has been prepared for the formation of conditioned reflexes. Initially, they formed slowly. On the 23rd week of life produced a conditioned reflex to the vestibular position for breastfeeding and rocking in the cradle. Then there is a rapid accumulation of conditioned reflexes, formed from all analyzers and reinforces the dominant food. The conditioned reflex to sound stimulus in the form of a protective (blinking) eyelid movement formed by the end of the 1st month of life, and the food reflex to sound stimulus - on the 2nd. At the same time formed and conditioned reflex to light.

brain nerve myelination

Links to the sources

1. (Stuart HC, Stevenson SS. In: Physical Growth and Development.5th Edn. Nelson, editor. Mitchell-Nelson Textbook of Pediatrics; Philadelphia: 1950. 1959. Reprinted in Documents-Geigy, Scientific Tables)

2. (An Overview of Anatomical Considerations of Infants and Children in the Adult World of Automobile Safety Design, Donald F. Huelke, Annu Proc Assoc Adv Automot Med. 1998; 42: 93-113.)

Размещено на Allbest.ru