Characteristics of the children's nervous system

2021-01-30 12:00 AM

The infant's brain has a relatively larger weight than an adult's (infant brain weighs 370 - 390g, accounts for 12-13% of body weight, while the adult brain weighs 1400g

Anatomical and structural features of the children's nervous system

Brain

The neural tube is formed from day 18 of the embryo from the epidermis. The upper part (the first part) of the neural tube is developed into the brain, the lower part becomes the spinal cord.

From the beginning of the neural tube, the brain is formed and goes through 3 phases, each stage forms a brain sac, from the brain sacs will form the brain's faeces:

The posterior cerebral sac makes up the brain, brain, cerebellum and ventricle IV.

The medial cerebral sac forms the cerebral stem, the quadriplegic tubule and the Silvius drain.

The anterior pocket creates two cerebral hemispheres, the lateral ventricle, the III ventricle, the vision change, the lower region and the pituitary gland.

The cerebral cortex begins to develop from the 3rd month of the embryo, continues to develop until the baby is born and basic functions are differentiated up to 8 years old.

The infant brain has a relatively larger weight than an adult's (infant brain weighs 370 - 390g, accounts for 12-13% of the body weight, while the adult's brain weighs 1400g, accounting for 2.3-2., 8% of body weight). Children's brains develop rapidly in the first year, brain weight is doubled at 1 year old after 9 years brain weight increases slightly.

The surface of a newborn's brain is full of lobe channels like adults, but the grooves are even shallower. Later, the strong development of the cerebral cortex made the grooves deeper.

When the child is born, the nervous system is the least developed of the segments. The brain is immature because the axons have not been myelinated. Myelin is the fat that surrounds the nerves. In addition to protecting the nerve impulses from spreading to other nerve fibers (such as the insulating sheath), the myelin sheath also maintains the rate of the axon's active voltage conduction (makes transmission of pulses faster). Although myelinization begins in the anterior and posterior roots of the spinal cord from the 4th month of the embryo, it is not until the 6th month postpartum that it is myelinated in the fibers that carry down the bundle and bind when the child is 4 years old. Therefore, in young children, the Babinski reflex can still be positive but does not indicate the damage to the pyramid, but only a physiological manifestation.

The infant's brain has about 14 billion cells (there are data that the brain has 17 billion cells) as an adult, the cortex is divided into 6 layers, but until the age of 8, the cells are completely ized. full as adults. At first, brain development is mainly focused on subcortical centres (such as striatum, vision, gray nucleus), after which the cerebral cortex and neocortex (new striatum) are formed and developed.

It is difficult for an infant's brain to distinguish between grey matter and white matter because the nerve cell body encroaches on the white matter.

The capillary network in the brain of a newborn develops strongly, the blood flow to the brain is large, the blood vessel wall is still fragile.

Children's brains are full of water, proteins and lipids. Up to 2 years old, the brain chemistry of a new child as in an adult.

Cerebellum

Differentiation of nerve cells in the cerebellar hemisphere ends about 9-11 months. The cerebellum develops simultaneously with the development of the motor organs. The cerebellum has the function of automatically regulating movement, muscle tone, balance and coordination of movements. Therefore, children often can stand and walk after 9 months, and can only perform a combination of movements such as dancing, balancing ... after 3-4 years old.

Spinal cord

Appearance: Spinal cord is cylindrical, slightly flat anterior and posterior direction.

The spinal cord has a direction of curving like a spine: The neck is bent backwards; the back is concave forward. The infant spinal cord tip is located relatively low, on par with the III lumbar vertebra, while in adults - horizontal to the II lumbar vertebrae.

The weight of the infant's spinal cord is 2 - 6 g; 5-year-old children increased 3 times; 15 years old children reach 24 - 30g as adults.

Cerebrospinal fluid

The amount of cerebrospinal fluid for infants is 15 - 20 ml, children at 1 year old are 35 ml, and adults are 120 - 150 ml.

Cerebrospinal fluid colour in a newborn may be slightly yellow, coinciding with the stage of physiological jaundice.

The protein in the infant's cerebrospinal fluid is slightly high (0, 4 - 0.8g / l), so the Pandey reaction may be mildly positive.

WBC count:

Premature babies can have up to 50 WBCs / mm3.

Infants can have up to 30 leukocytes / mm3.

Adults, mostly lymphocytes of no more than 5 leukocytes/mm 3.

Cerebrospinal fluid is produced from clusters of capillaries in the lateral ventricles. From there, cerebrospinal fluid passes through the Monroe hole into the third ventricle, continues through the Sylvius drain into the IV ventricle, through the Magendie hole and the Luska hole into the venous and subarachnoid sinuses of the brain and spinal cord - where they will be destroyed gradually. As a result, any disorder associated with proliferation, decreased extinction or a delay in cerebrospinal fluid circulation can lead to hydrocephalies (Hydrocephaly).

H Stand neurovegetative

The real nervous system is composed of two sympathetic and parasympathetic systems. They work immediately after childbirth, in which the sympathetic nervous system dominates.

Sympathetic system (denoted by ɛ):

Strings of fibres from lateral horn centres spinal grey matter

belongs to the segments from lumbar segment 1 (L1) to segment lumbar 3 (S3).

The nodule of the sympathetic system is located near the centre, but far from the organ.

Most organs contain 8 fibres, except for the pancreas (multiply ɛ 'fibres only).

The parasympathetic system (denoted by ɛ '):

Including fibres derived from the nuclei Edinger - Westphel (brain stem), the upper saliva nucleus, the lower saliva nucleus, the dorsal nucleus (the brain) and then follow the cranial nerve III, VII, IX and X.

The fibres originate from the centres in the anterior horns of the spinal grey matter that belong to the same segments 1 - 4.

The nodule of the parasympathetic system is located far from the centre, such as near or within the organs.

Most organs contain fibres \ except womb (multiply s fibres only).

Physiological and pathological features of the children's nervous system

Physiological characteristics

Since brain cells have not yet differentiated, nerve axons have not been myelinated, the response of the cerebral cortex tends to spread: Any small stimulus can cause a systemic reaction ( capture reaction example).

In the infancy period, due to the weak ability of euphoria of the cerebral cortex, environmental stimuli are often excessive, leading to protective inhibition, the child sleeps during this period (sleeping from 20-22 hour/day).

Since the new cortex and striatum are underdeveloped, the subcortical activities prevail. Therefore, in newborns, there can be extrapyramidal movements such as dancing, abnormal limb movement.

In newborns, because the medulla, peripheral nerves, and optic nerve have been myelinated, the baby has reflexes to suck, swallow, cry and look at a fixed point. But because the myelin process is incomplete, some reflexes that are pathological in older children are physiological in young children (like the Babinski reflex).

In the early years, to ensure that the brain can develop rapidly in volume and quality, the demand for oxygen and cerebral circulation is higher than that of adults.

EEG also changes with age:

Infants: Centralized EEG activity in the peak and central regions, delta waves 0.5 - 3 cycles/second, voltage 20 - 50 microvolts, uneven waves, not simultaneously.

Children under 1-year-old: Electro-brain activities are mostly delta waves; occipital region appears theta wave 3-7 cycles/sec.

Children 1-3 years old: EEG activity is theta wave 3-7 cycles/second, voltage 30 - 50 microvolts.

Children aged 4 years and older: Theta waves gradually decrease, appear alpha waves 8-12 cycles / second, amplitude 30-50 microvolts.

Pathological characteristics

Because the cells have not been differentiated, the chemical composition has a lot of water, so it is easy to have meningeal reactions and more severe reactions when infected or poisoned.

Characteristics of cerebral capillaries in young children thrive, thin vessel walls and susceptible to hypoxia, so meningeal haemorrhage easily occurs.

Because the brain of a young child contains a lot of water, is located in the skull is not sure, so a small injury such as a fall, falling from a standing position can cause hippocampus, herniation between the two. hemisphere or nerve axis damage leading to clinical hemiplegia.