Section 1, Article 2 - When a baby is born, one hundred billion neurons are present and accounted for. They have been busily firing messages within the child’s nervous system since about the fourth month of life (). All five senses function within the womb, allowing the pre-born child to touch, taste, smell, hear, feel, and even see long before their comfortable existence is disrupted by birth. It appears that some thought processes are also functioning as children have learned to recognize their mother’s voice, preferring this sound above all others soon after birth (). In spite of all this prenatal activity, much development in the brain remains undone when the child is born. In fact, more growth in brain volume and structure takes place between birth and the child’s second birthday than at any other period of time in life.
Before we begin analyzing the process of development within the brain and nervous system, let’s begin by reviewing basic brain physiology. The brain is divided into two halves, or hemispheres. The hemispheres are divided into four parts, or lobes, with each area of the brain uniquely “wired” for specific tasks. The frontal lobe controls voluntary movement, thinking, personality, and goal-directed behavior; the temporal lobe controls hearing language processing, and memory; the occipital lobe controls vision; and the parietal lobe controls sensory processing. The cortex forms the outer layer of these structures. It is the part of the brain where thinking, analyzing, feeling, and planning take place (). At birth, the ability to touch, smell, and taste which are controlled by the cortex are all present and functioning. Sensory areas of the cortex mature first, followed by the motor areas. Both of these regions are fairly well-developed by a child’s second birthday. The frontal lobes, those responsible for higher-order thinking, are still developing throughout childhood, adolescence, and into the mid-twenties (; ).
Neurons are the most basic part of the nervous system (some call neurons the “building blocks” of the nervous system). Each neuron is a single cell designed to transmit messages throughout the body. Each neuron has three parts: the cell body, the axon, and dendrites. Neurons communicate by transmitting electrical impulses from the cell body down the axon to a gap or space called the synapse. Neurotransmitters, chemicals that facilitate the transfer of the electrical impulse, help the impulse leap across the synapse to the dendrites of other neurons. The dendrite provides a path to the next neuron’s cell body
Critical changes take place in the brain beginning at birth and continue throughout childhood and adolescence (; ; ). The most dramatic change that takes place in the first two years of life is in the growth of the communication network through a proliferation of synapses and dendrites, and through the process of myelination. Immediately after birth, and continuing through the child’s second birthday, the brain is developing this important network. In fact, 83% of the connections used throughout one’s life are formed during the first two years (). This period of growth involves not only the creation of connectors (dendrites) but also the destruction of many of these dendrites in a process called pruning (; ; ). Dendrites that are unused in the brain are “pruned”; dendrites that are not strengthened through use will wither and die during this period of time.
There is no question that proper brain development is crucial to a child’s survival. In fact, the body itself has a built-in mechanism to nourish and protect the brain during times of extreme physical deprivation. If an infant or young child is starving, the body will first direct available nutrients to the brain in a process called head-sparing. Even if the rest of the body wastes away due to starvation, the brain is protected for a time. Another issue related to protection and harm is a tragic condition called shaken baby syndrome. It results when a caregiver shakes the baby violently. Blood vessels in the brain are damaged, and neural connections break. Long term injury to the brain or death results. Other factors that can help or hurt brain development are nutrition and sleep.