The article discusses the age-related features of the development of the nervous system in children and their impact on the clinical manifestations of neurological diseases. Data on the formation of the central nervous system at various stages of growth and the features of the structure and functioning of the brain in childhood are presented. Particular attention is paid to the most common neurological pathologies in children, including malformations, convulsive syndrome, hypertensive-hydrocephalic syndrome, and hyperactivity syndrome. The importance of timely detection of deviations from age norms for early diagnosis and selection of the correct treatment tactics is emphasised.

Introduction

Age-related features of the nervous system are an important aspect in the propaedeutics of childhood diseases. The nervous system of a child differs from that of an adult not only in its anatomical structure, but also in its functional activity, degree of maturity, and reactivity. These differences determine the uniqueness of the clinical picture of many diseases in childhood. Understanding the stages of development of the nervous system, as well as age norms and time limits for the appearance and disappearance of physiological reflexes, allows the doctor to more accurately assess the condition of the child, identify deviations in a timely manner and make a correct diagnosis.

Objective : To study the anatomical, physiological, and functional characteristics of the nervous system in children.

Materials and methods: Analysis of scientific studies cited in the PubMed, Cyberleninka, and National Library of Medicine databases.

Results and discussion: Antenatal period The central nervous system (CNS) consists of the brain and spinal cord. Both develop from the embryonic ectoderm along with other structures, such as the skin. Their development begins as early as the 3rd and 4th weeks of embryonic life, starting with the process of neurulation, which is the development of the neural tube. The neural tube spontaneously closes rostrally and caudally. In the fifth to sixth week, when the brain first appears, proencephalic development occurs. The primitive brain consists of the proencephalon, midbrain, and rhombencephalon. The proencephalon is further divided into the telencephalon and diencephalon through a series of developmental stages, namely: formation, fragmentation, and development of the midline.

At birth, the brain is large relative to body weight: in a newborn, it is 1/8–1/9 per 1 kg of body weight; in a 1-year-old child, it is 1/11–1/12; in a 5-year-old child, it is 1/13–1/14; and in an adult, it is 1/40. The convolutions are well defined, the furrows are large, but have little height and depth. Small furrows appear after birth. For every 1 kg of a newborn's weight, there are 109 g of brain matter. An adult has only 20–25 grams. By 9 months, the brain mass doubles, by 3 years it triples, and then from 6–7 years the growth rate slows down. The cerebral cortex matures by 5–6 years. [2]

The younger the child, the faster the nervous system develops. It is particularly vigorous during the first 3 months of life. The differentiation of nerve cells is complete by the age of 3, and by the age of 7–8, the structure of the cerebral cortex is almost identical to that of an adult. Myelination of the nerves is complete by the age of 5: intracranial nerves by 3–4 months, cranial nerves by 1 year and 3 months, pyramidal tracts by 2–3 years, and vagus nerves by 3–4 years. The medulla oblongata is more developed functionally than other parts at an early age: almost all of its centres are active — respiration, heart and vascular regulation, sucking, swallowing, coughing, sneezing. The chewing centre begins to function somewhat later. In the regulation of muscle tone, the activity of the vestibular nuclei is reduced (the tone of the extensors is reduced). By the age of 6, the differentiation of neurons and the myelination of fibres are completed in these centres, and the coordination of the centres is improved.

The following diseases contribute most significantly to the structure of CNS diseases in children:

– perinatal CNS damage (prevalence — 60: 1000); epilepsy (7: 1000);

– hereditary degenerative and metabolic diseases of the nervous system (1:3000 live births);

– progressive muscular dystrophies (3.5:1000);

– developmental abnormalities (3:1000); neuropsychiatric problems — cognitive and behavioural disorders (16:1000) [6]

Cerebral cortex malformations (CCM) – are macroscopic or microscopic abnormalities of the cerebral cortex that arise as a result of interruption of the normal stages of formation of the cortical plate. In most cases, they are genetically determined, but other intrauterine factors may also cause them: infection, hypoxia, intoxication. [8]

The classification of CPD is based on three main events in the formation of the cerebral cortex:

– proliferation of neurons and glia in the ventricular and subventricular zones;

– migration of immature but postmitotic neurons to the developing cerebral cortex;

– cortical organisation.

Currently, the revised classification of PRKGM proposed by A. J. Barkovich et al.

Holoprosencephaly is a malformation of the forebrain characterised by incomplete separation of the two cerebral hemispheres. Chromosomal abnormalities, such as Patau and Edwards syndromes, carry a higher risk of holoprosencephaly, as do complications of pregnancy with diabetes. Patau syndrome (trisomy 13) is the most commonly associated syndrome. Holoprosencephaly is usually incompatible with life, and most children born with this malformation have a very high mortality rate in the early postnatal period. Subtypes of holoprosencephaly in order of increasing severity are: midline, lobar, semi-lobar, and allobar variants. Brain CT or MRI can confirm the diagnosis and differentiate between subtypes of holoprosencephaly. It is believed that genes such as bone morphogenetic protein (BMP), Sonic hedgehog (Shh), and fibroblast growth factor (FGF) are associated with holoprosencephaly. [4]

1. Hypertensive-hydrocephalic syndrome. Hypertensive syndrome (increased intracranial pressure) in children is often combined with hydrocephalic syndrome, which is characterised by enlargement of the ventricles in the subarachnoid space as a result of the accumulation of excess cerebrospinal fluid. Increased intracranial pressure in infants can be transient or permanent, and hydrocephalus can be compensated or subcompensated, which accounts for the wide range of clinical manifestations. Neurological symptoms in hypertensive-hydrocephalic syndrome depend both on the severity of the syndrome and its progression, as well as on the brain changes that caused it. In hypertensive syndrome, the first thing to change is the behaviour of children. They become easily excitable, irritable, their cries become sharp and piercing, their sleep becomes shallow, and they wake up frequently. With hydrocephalic syndrome, on the contrary, children are lethargic and snotty. Loss of appetite, regurgitation, and sometimes even vomiting can lead to weight loss. [6]
2. Hyperactivity syndrome. The main manifestations of hyperactivity syndrome are motor restlessness, emotional lability, sleep disturbances, increased reflex excitability, and a tendency toward a lowered seizure threshold. These children may not show significant delays in psychomotor development, but a thorough examination usually reveals some mild abnormalities. Psychomotor development disorders in hyperactivity syndrome are characterised by delays in the formation of voluntary attention and differentiated motor and mental reactions, which gives psychomotor development a peculiar unevenness.
3. Seizure syndrome is an emergency condition in neurological, paediatric and general medical practice that is classified as a potentially life-threatening disorder in children, adolescents and adults. In the continuing medical education (CME) system, this emergency condition is included in the postgraduate training programme for neurologists, paediatricians, general practitioners, emergency doctors, anaesthesiologists and resuscitators. The pathogenesis of seizures involves changes in neuronal activity in the brain (abnormal, high-amplitude, and periodic bioelectrical activity of the brain) and the process of depolarisation of brain neurons, disruption of thalamocortical interaction, and changes in the functional state of the dentate nucleus in the subcortical region of the brain. [7]

Conclusion

Age-related features of the nervous system's development play a key role in understanding the clinical manifestations of its diseases in children. At each stage of a child's growth, significant changes occur in the anatomical and physiological structure and functions of the central and peripheral nervous systems. These changes determine the specific symptoms, course, and prognosis of neurological diseases. Early detection of disorders such as congenital malformations, convulsive syndrome, hypertensive-hydrocephalic syndrome, or signs of hyperexcitability requires the physician to be knowledgeable about age norms and able to interpret even minimal deviations.

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