4.2: Rapid Physical Changes

Rapid Physical Changes

Fig. 4.2. Baby's growth from birth to one-year

Image Source: Perpetual Fostering. Child Development Stages. Wikimedia Commons.

As mentioned in the previous chapter, the average newborn in the United States weighs about 7.5 pounds and is about 20 inches in length at birth. In the following days they may experience a 5% weight loss. in the first few days is followed by a period of rapid growth.

• age 4 months: the infant will have doubled in weight
• age 12 months: the infant tripled its birth weight
• age 24 months: the infant's weight has quadrupled

The average length of the infant at one year is about 26-32 inches.

Hormones and Growth

Two hormones are very important to this growth process. The first is Human Growth Hormone (HGH) which influences all growth except that in the Central Nervous System (CNS). The hormone influencing growth in the Central Nervous System (CNS) is called Thyroid Stimulating Hormone (TSH). Together these hormones influence the growth in early childhood.

These hormones are released as babies sleep each night and as a result, children need 11 to 14 hours of sleep from ages 2-6 years old. Because seep is so important to the growth process, establishing rituals to signal to the baby that it's time to sleep helps them wind down and get the sleep they so desperately need. Examples of rituals, depending on the age of the child may be reading a story, taking a bath, brushing teeth, etc.

Proportions of the Body

Figure 4.2.1 – Body proportions from infancy to adulthood.

Image Source: Growth and Development. NurseKey. From Patton KT, Thibodeau GA: The human body in health and disease, ed 6, St Louis, 2014, Mosby.)

Another dramatic physical change that takes place in the first several years of life is the change in body proportions. The head initially makes up about 50 percent of our entire length when we are developing in the womb. At birth, the head is about 25% of our length. Imagine now how difficult it must be to raise one’s head during the first year of life! If you have ever seen a 2 to 4-month-old infant lying on the stomach trying to raise the head, you know how much of a challenge this is.

Fig. 4.2.2. Baby laying on tummy holding her head up.

Image Source: Dean Wissing. Molly and Lisa. Wikimedia Commons.

Brain Development

Some of the most dramatic physical change that occurs during this period is in the brain. At birth, the brain is about 25% of its adult weight which is not true for any other part of the body. It DOUBLES in size during the first year of life. By age 2, it is at 75% its adult weight, and 95% by age 6 and finally 100% by age 7.

Fig. 4.2.3. MRI of baby's brain from birth to 2 years of age.

Image Source: Fetal, Infant, & Toddler Neuroimaging Group—FIT’NG Mostapha & Styner 2019, Magnetic Resonance Imaging. @FIT_NGIn X.com. Feb. 2021.

MRI scans of a baby's brain over the first two years shows the first year of life represents the period of greatest brain volume growth in typical children, with slower growth during the second year of life.

While most of the brain’s 100 to 200 billion neurons are present at birth, they are not fully mature and during the next several years dendrites or connections between neurons will undergo a period of temporary dramatic growth.

Fig. 4.2.4.Diagram of basic neuron and components.

Image Source: Jennifer Walinga. Components of neuron. Wikimedia Commons.

As a person talks, sings and interacts with a baby, the baby reacts to these events, taking in information, processing it and storing it. The synapses (connections) and the pathways formed actively create a web of learning in the brain. Therefore, early responsive experiences are so crucial. Those synapses that have been activated many times tend to become permanent to ensure optimal social-emotional, language and cognitive growth.

There is a proliferation of these dendrites during the first two years so that by age 2, a single neuron might have thousands of dendrites. After this dramatic increase, the neural pathways that are not used will be eliminated thereby making those that are used much stronger. Because of this proliferation of dendrites, by age 2 a single neuron might have thousands of dendrites.

Synaptogenesis, or the formation of connections between neurons, continues from the prenatal period forming thousands of new connections during infancy and toddlerhood. This period of rapid neural growth is referred to as Synaptic Blooming. This activity is occurring primarily in the cortex or the thin outer covering of the brain involved in voluntary activity and thinking.

The prefrontal cortex that is located behind our forehead continues to grow and mature throughout childhood and experiences an additional growth spurt during adolescence. It is the last part of the brain to mature and will eventually comprise 85% of the brain’s weight. Experience will shape which of these connections are maintained and which of these are lost. Ultimately, about 40% of these connections will be lost. As the prefrontal cortex matures beyond infancy and toddlerhood throughout childhood and adolescence the child is increasingly able to regulate or control emotions, to plan activity, strategize, and have better judgment.

Another major change occurring in the central nervous system is the development of myelin, a coating of fatty tissues around the axon of the neuron. Myelin helps insulate the nerve cell and speed the rate of transmission of impulses from one cell to another. This enhances the building of neural pathways and improves coordination and control of movement and thought processes. The development of myelin continues into adolescence but is most dramatic during the first several years of life.

Brain Lobes

Fig. 4.2.5. Brain Lobes.

Image Source: Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

Each side of your brain is comprised of four lobes:

• occipital
  • primarily responsible for vision.
• temporal
  • temporal lobe processes memories, integrating them with sensations of taste, sound, sight and touch
• frontal
  • important for cognitive functions and control of voluntary movement or activity
• parietal
  • processes information about temperature, taste, touch and movement

Strong brain architecture supports the development of integrated cognitive, social, and emotional skills called executive function. A good analogy is to think of this as an air traffic controller in a child’s mental airspace.

Executive functions process

• what needs attention
• how to plan ahead,
• how to follow rules and
• how to manage conflicts

As you can imagine, until this is fully developed the child is “wired” to have many behavior challenges. It is important to help young children build these skills and form strong brains.

Optimal and Critical Periods of Brain Development

Our understanding of windows of opportunities has made a difference in how we view the importance of the early years. These are periods in the development of the brain when specific types of learning take place. The brain development in the first three years is a foundation for the child to build on for developing capacity for learning and loving. These windows are more difficult to open and use as the child ages.

These optimal and critical periods exist for

• vision
• hearing
• math and logic
• language - birth to age 10
• emotional development

For example, the optimal and critical period window for language is birth to 10 years but the circuits in the auditory section of the brain are wired by age 1. The more words a child hears in a meaningful way by age 2, the larger the child’s vocabulary will be. Think about the impact of that for caregivers of infants and toddlers and on the importance of proper hearing screenings.

Trauma, Toxic Stress and Cortisol

This is also the time to reduce a young child’s stress levels. The experiences a child has can affect how the brain is structured and even the physical size of the brain. Toxic stress -- when a child experiences strong, frequent, and/or prolonged adversity—

• physical or emotional abuse
• chronic neglect,
• caregiver substance abuse
• caregiver mental illness
• exposure to violence
• accumulated burdens of family economic hardship

Without adequate adult support changes the architecture of the brain and other organs and causes impairment. Toxic stress releases high levels of cortisol into the system which can have long lasting health effects. However, it is important to remember that children are very resilient. There are many ways children can overcome challenging starts in life.

Fig. 4.2.6. Parents and baby interaction (serve and return).

Image Source: Anna Shvets. Parents playing with their baby. Pexels.com

Serve and Return Interactions

Serve and return interactions shape brain architecture. When an infant or young child babbles, gestures, or cries, and an adult responds appropriately with eye contact, words, or a hug, neural connections are built and strengthened in the child’s brain that support the development of communication and social skills. Much like a lively game of tennis, volleyball, or Ping-Pong, this back-and-forth is both fun and capacity-building.

When caregivers are sensitive and responsive to a young child’s signals and needs, they provide an environment rich in serve and return experiences. Because responsive relationships are both expected and essential, their absence is a serious threat to a child’s development and well-being. Healthy brain architecture depends on a sturdy foundation built by appropriate input from a child’s senses and stable, responsive relationships with caring adults.

If an adult’s responses to a child are unreliable, inappropriate, or simply absent, the developing architecture of the brain may be disrupted, and subsequent physical, mental, and emotional health may be impaired. The persistent absence of serve and return interaction acts as a “double whammy” for healthy development: not only does the brain not receive the positive stimulation it needs, but the body’s stress response is activated, flooding the developing brain with potentially harmful stress hormones.

Building the capabilities of adult caregivers can help strengthen the environment of relationships essential to children’s lifelong learning, health, and behavior. A breakdown in reciprocal serve and return interactions between adult caregivers and young children can be the result of many factors. Adults might not engage in serve and return interactions with young children due to significant stresses brought on by financial problems, a lack of social connections, or chronic health issues.

Sources

• Lifespan Development - Module 4: Infancy by Lumen Learning references Psyc 200 Lifespan Psychology by Laura Overstreet, licensed under CC BY 4.0.
• Serve and Return. Center for the Developing Child. Harvard University.