HG&D: Chapter 5 Body Changes (pgs. 121-125)

Average North American newborn: -20 in (51 cm) -7 lbs (3 Average North American newborn: -20 in (51 cm) -7 lbs (3.2 kg) The phenomenon in which inadequate nutrition causes the body to stop growing but not the brain is called head-sparing.

A standard, or average, of physical development that is derived for a specific group or population is a norm. By age 2, the typical child weighs about 30 lbs (13 kg) and measures 32-36 in (81-91 cm). The typical 2-year-old is almost 1/5 (20%) of his or her adult weight and half (50%) of his or her adult height.

A percentile is a point on a ranking scale of 1 to 99 A percentile is a point on a ranking scale of 1 to 99. Throughout childhood, regular and ample sleep correlates with maturation of the: Brain Learning Emotional regulation And psychological adjustment in school and within the family. Approximately 80% of 1-year-olds sleep through the night.

Over the first months of life, the relative amount of time spent in the different stages of sleep changes. The stage of sleep characterized by flickering eyes behind closed lids and dreaming is called REM sleep.

During this stage of sleep brain waves are fairly rapid During this stage of sleep brain waves are fairly rapid. This stage of sleep decreases over the first months, as does the dozing stage called transitional sleep. Slow-wave sleep, also called quiet sleep, increases markedly at about 3 or 4 months of age.

Early Brain Development (pgs 125-130)

At birth, the brain has attained about 25% of its adult weight; by age 2 the brain is about 75% of its adult weight. In comparison, body weight at age 2 is about 20% of what it will be in adulthood.

The brain’s communication system consists primarily of nerve cells called neurons connected by intricate networks of nerve fibers, called axons and dendrites. About 70% of these cells are in the brain’s outer layer called the cortex. Each neuron has many dendrites but only a single axon.

Neurons communicate with one another at intersections called synapses Neurons communicate with one another at intersections called synapses. After traveling down the length of the axon, electrical impulses excite chemicals called neurotransmitters that carry information across the synaptic gap to the dendrite of a “receiving” neuron. Most of the nerve cells are present at birth whereas the fiber networks are rudimentary.

During the first months of life, brain development is most noticeable in the cortex. From birth until age 2, the density of dendrites in the cortex increases by a factor of 5. The phenomenal increase in neural connections over the first two years has been called transient exuberance.

Following this growth process, neurons in some areas of the brain wither in the process called pruning because experience does not activate those brain areas.

Brain functions that require basic common experiences in order to develop are called experience-expectant brain functions; those that depend on particular, and variable, experiences in order to develop are called experience-dependent brain functions.

(Thinking Like a Scientist) Neuroscientists once believed that brains were entirely formed by genes and prenatal influences; today, most believe in plasticity, which is the concept that personality, intellect, habits, and emotions change throughout life for a combination of reasons.

William Greenough discovered that the brains of rats who were raised in stimulating environments were better developed, with more dendrite branching, than the brains of rats raised in barren environments.

Orphaned Romanian children who were isolated and deprived of stimulation showed signs of emotional damage. Placed in healthier environments, these children improved; years later, persistent deficits in these children were found.