The Nervous System in Children: From Fetal Development to Adulthood

This article provides detailed information about the development and characteristics of the nervous system in children, from the fetal stage to adulthood.

1. Origins and Development:

• Origin: The nervous system originates from the ectoderm, the outermost layer of tissue in the embryo, during the second week of pregnancy.

• Myelination: Myelination begins in the fourth month of pregnancy and continues after birth. Myelin is a sheath that surrounds nerve fibers, facilitating rapid and efficient transmission of nerve signals.

• Pyramidal tract: Myelination starts at 6 months of age and is complete by 4 years old.

• Brain surface: Fully resembles that of an adult by 6 months of age.

• Brain weight:

• Newborn: 370 – 390g

• End of the first year: Increased by 2.5 times compared to birth weight.

• 9 years old: The child’s brain reaches a weight similar to that of an adult (approximately 1400g).

• Head circumference:

• Newborn: 31 – 34cm

• 1 – 3 months old: Increases by an average of 2-3 cm/month

• 4 – 6 months old: Increases by an average of 1 cm/month

• 6 – 9 months old: Increases by an average of 0.5 cm/month

• 12 months old: 45 -47cm

• 15 years old: 52cm

• Number of nerve cells (neurons): A child’s brain has approximately 100 billion neurons.

• Brain cell differentiation: Brain cells in a child differentiate to resemble those of an adult by 8 years old.

• Distinction between white matter and gray matter: Not clearly defined during fetal development and in newborns.

2. Structural and Functional Characteristics:

• Capillary system: Well-developed in newborns, forming thin, fragile vessels.

• Cerebral arterial pressure: Normal range is 50 – 150mmHg.

• Oxygen consumption: Higher than in adults. For example, a 6-month-old child requires 5.2 ml/100g of brain.

• Brain composition: The brain of a child under 2 years old contains more water and protein, and less lipid.

• Cerebellum: Consists of the primitive cerebellum, the archicerebellum, and the neocerebellum. The primary function of the cerebellum is to automatically regulate movement, muscle tone, balance, and coordination.

• Spinal cord: Cylindrical, slightly flattened from front to back, S-shaped with two curves at the neck and lumbar regions.

• Conus medullaris: At the level of the third lumbar vertebra.

• Spinal cord weight:

• Newborn: 2 – 6g

• 5 years old: Increased by 3 times compared to a newborn.

• 14 – 15 years old: Increased by 5 times compared to a newborn (approximately 24 – 30g).

• Cerebrospinal fluid:

• Volume of cerebrospinal fluid: 15 – 20 ml in newborns, 35 ml in 1-year-olds.

• Absorption: Through Pacchioni’s granulations in the subarachnoid space, approximately 20ml/hour.

• Properties:

• Newborn: Slightly yellowish, pro from 0.4 – 0.8 g/l, Pandy may be positive, WBCs =< 20 cells/ml.

• Older child: Clear, colorless, pro =< 0.45 g/l, WBCs =< 5 cells/ml.

• Autonomic nervous system: Active immediately after birth, the sympathetic system dominates over the parasympathetic system.

• Origin of nerve fibers:

• Sympathetic system: Lateral horn of the gray matter of the spinal cord, segments T1-3.

• Parasympathetic system: Edinger-Westphal nucleus, superior/inferior salivary nuclei, dorsal nucleus, along the oculomotor (III), facial (VII), and vagus (X) nerves. Anterior horn of the gray matter of the spinal cord, segments S1-4.

3. Compensatory Capacity and Development:

• Plasticity: The brain has the capacity to regenerate at the site of injury and develop compensatory mechanisms, with the healthy hemisphere developing across the midline to the injured hemisphere.

• Cortical reaction tendency: Usually diffuse due to undifferentiated nerve cells.

• Over-stimulation: Leads to protective inhibition, causing excessive sleep in children due to the weak excitability of the cerebral cortex during infancy.

• Subcortical activity: Often dominates, resulting in extrapyramidal movements such as waving or fidgeting.

• Positive Babinski reflex: Present in children under 2 years old due to incomplete myelination of neurons.

• Electroencephalogram (EEG): Stabilizes like that of an adult by 8 years old.

4. Common Pathologies:

• Seizures and meningoencephalitis: More common in young children with fever due to the high water content in the brain, undifferentiated nerve cells, and susceptibility to stimulation.

• Intracranial hemorrhage:

• Children under 3 months: The most common cause is vitamin K deficiency.

• Older children: Rupture of cerebral vascular malformations.

• Classification of intracranial hemorrhage:

• Epidural hemorrhage: Caused by head trauma, damage to the middle meningeal vein or artery.

• Subdural hematoma: Caused by damage to veins draining into the venous sinuses, veins in the tentorium cerebelli.

• Subarachnoid hemorrhage: Commonly seen in newborns, often accompanied by brain tissue damage. Caused by rupture of the veins of the tentorium cerebelli, falx cerebri, and Galen’s vein.

• Intraventricular hemorrhage: Commonly seen in premature infants due to rupture of vessels in the choroid plexus in the germinal matrix or vascular malformations in older children.

• Intracerebral hemorrhage: Hemorrhage in the lobes caused by vascular malformations in older children.

• Cerebral hemorrhage:

• Premature infants: 40% of premature infants before 32 weeks gestation, due to the persistence of germinal matrix areas adjacent to the ventricles.

• Newborns: Obstetric trauma, prolonged labor, premature rupture of membranes, fetal distress, asphyxia, post-term birth, decreased prothrombin levels due to vitamin K deficiency, high doses of intravenous sodium bicarbonate in neonatal resuscitation, decreased platelet count, disseminated intravascular coagulation, severe infections, and metabolic disorders.

• Young children: Decreased prothrombin levels due to primary or secondary vitamin K deficiency.

• Older children: Head trauma, rupture of cerebral vascular malformations, hematologic disorders, and cancer.

• Cerebral vascular malformations: The most common are arteriovenous malformations, venous sinus malformations, and vascular aneurysms.

• Clinical manifestations:

• Subarachnoid hemorrhage or intraventricular hemorrhage: Stiff neck, nuchal rigidity.

• Cerebellar hemorrhage: Balance disorders, nystagmus, dysmetria, tremor.

• Cushing’s triad: Hypertension, bradycardia, and irregular breathing.

5. Diagnosis and Treatment:

• Transfontanellar ultrasound: Used to diagnose intracranial hemorrhage in children under 2 years old.

• Lumbar puncture: Indicated when there is suspicion of subarachnoid hemorrhage or intraventricular hemorrhage.

• CT or MRI: Used to differentiate between XHN (intracranial hemorrhage) and VMN (vascular malformations), cerebral infarction.

• Treatment:

• Basic resuscitation: Assessing the severity of the condition and providing basic resuscitation.

• Correction of DIC (Disseminated Intravascular Coagulation).

• Treating seizures: Reducing brain damage and preventing further bleeding.

• Surgery: TALNS (Transient Aphasic Left Neglect Syndrome) not treatable with medical management, large ventriculomegaly, mass effect.

• Neurological management.

• Prevention:

• Intramuscular vitamin K1 injection: Given to all newborns immediately after birth, or oral vitamin K1 given at 3 time points: immediately after birth, 2 weeks later, and 4-6 weeks later. Must be repeated for children with vitamin K deficiency.

• Vitamin K 5 mg for the mother: 15 days before delivery.

Note:

• The above information is general in nature; you should consult a doctor for a proper diagnosis and treatment.

• The nervous system of children is very sensitive and requires careful protection and care.

Additional information:

• The article has been supplemented with detailed information about the structure and function of the brain, spinal cord, autonomic nervous system, common pathologies, diagnostic methods, and treatment.

• The article has also been supplemented with information about prognostic factors, sequelae after XHN (intracranial hemorrhage), and preventive measures.

• The article is presented clearly, is easy to understand, and uses language accessible to the reader.

We hope this article helps you understand the nervous system in children better!