Physical Development in Infancy and Toddlerhood

Physical Development in Infancy and Toddlerhood essay assignment

Physical Development in Infancy and Toddlerhood essay assignment

Infants acquire new motor skills by building on previously acquired capacities. Eager to explore her world, this baby practices the art of crawling. Once she can fully move on her own, she will make dramatic strides in understanding her surroundings.

chapter outline

·   Body Growth

·   Changes in Body Size and Muscle–Fat Makeup

·   Individual and Group Differences

·   Changes in Body Proportions

·   Brain Development

·   Development of Neurons

·   Neurobiological Methods

·   Development of the Cerebral Cortex

·   Sensitive Periods in Brain Development

·   Changing States of Arousal

Get solution to your nursing paper : Physical Development in Infancy and Toddlerhood

· ■  BIOLOGY AND ENVIRONMENT  Brain Plasticity: Insights from Research on Brain-Damaged Children and Adults

· ■  CULTURAL INFLUENCES  Cultural Variation in Infant Sleeping Arrangements

·   Influences on Early Physical Growth

·   Heredity

·   Nutrition

·   Malnutrition

·   Learning Capacities

·   Classical Conditioning

·   Operant Conditioning

·   Habituation

·   Imitation

·   Motor Development

·   The Sequence of Motor Development

·   Motor Skills as Dynamic Systems

·   Fine-Motor Development: Reaching and Grasping

·   Perceptual Development

·   Hearing

·   Vision

·   Intermodal Perception

·   Understanding Perceptual Development

· ■  BIOLOGY AND ENVIRONMENT  “Tuning In” to Familiar Speech, Faces, and Music: A Sensitive Period for Culture-Specific Learning

On a brilliant June morning, 16-month-old Caitlin emerged from her front door, ready for the short drive to the child-care home where she spent her weekdays while her mother, Carolyn, and her father, David, worked. Clutching a teddy bear in one hand and her mother’s arm with the other, Caitlin descended the steps. “One! Two! Threeee!” Carolyn counted as she helped Caitlin down. “How much she’s changed,” Carolyn thought to herself, looking at the child who, not long ago, had been a newborn. With her first steps, Caitlin had passed from infancy to toddlerhood—a period spanning the second year of life. At first, Caitlin did, indeed, “toddle” with an awkward gait, tipping over frequently. But her face reflected the thrill of conquering a new skill.

As they walked toward the car, Carolyn and Caitlin spotted 3-year-old Eli and his father, Kevin, in the neighboring yard. Eli dashed toward them, waving a bright yellow envelope. Carolyn bent down to open the envelope and took out a card. It read, “Announcing the arrival of Grace Ann. Born: Cambodia. Age: 16 months.” Carolyn turned to Kevin and Eli. “That’s wonderful news! When can we see her?”

“Let’s wait a few days,” Kevin suggested. “Monica’s taken Grace to the doctor this morning. She’s underweight and malnourished.” Kevin described Monica’s first night with Grace in a hotel room in Phnom Penh. Grace lay on the bed, withdrawn and fearful. Eventually she fell asleep, gripping crackers in both hands.

Carolyn felt Caitlin’s impatient tug at her sleeve. Off they drove to child care, where Vanessa had just dropped off her 18-month-old son, Timmy. Within moments, Caitlin and Timmy were in the sandbox, shoveling sand into plastic cups and buckets with the help of their caregiver, Ginette.

A few weeks later, Grace joined Caitlin and Timmy at Ginette’s child-care home. Although still tiny and unable to crawl or walk, she had grown taller and heavier, and her sad, vacant gaze had given way to an alert expression, a ready smile, and an enthusiastic desire to imitate and explore. When Caitlin headed for the sandbox, Grace stretched out her arms, asking Ginette to carry her there, too. Soon Grace was pulling herself up at every opportunity. Finally, at age 18 months, she walked!

This chapter traces physical growth during the first two years—one of the most remarkable and busiest times of development. We will see how rapid changes in the infant’s body and brain support learning, motor skills, and perceptual capacities. Caitlin, Grace, and Timmy will join us along the way to illustrate individual differences and environmental influences on physical development.

Get solution to your nursing paper : Physical Development in Infancy and Toddlerhood

TAKE A MOMENT…  The next time you’re walking in your neighborhood park or at the mall, note the contrast between infants’ and toddlers’ physical capabilities. One reason for the vast changes in what children can do over the first two years is that their bodies change enormously—faster than at any other time after birth.

Changes in Body Size and Muscle–Fat Makeup

By the end of the first year, a typical infant’s height is about 32 inches—more than 50 percent greater than at birth. By 2 years, it is 75 percent greater (36 inches). Similarly, by 5 months of age, birth weight has doubled, to about 15 pounds. At 1 year it has tripled, to 22 pounds, and at 2 years it has quadrupled, to about 30 pounds.

FIGURE 4.1 Body growth during the first two years.

These photos depict the dramatic changes in body size and proportions during infancy and toddlerhood in two individuals—a boy, Chris, and a girl, Mai. In the first year, the head is quite large in proportion to the rest of the body, and height and weight gain are especially rapid. During the second year, the lower portion of the body catches up. Notice, also, how both children added “baby fat” in the early months of life and then slimmed down, a trend that continues into middle childhood.

Figure 4.1  illustrates this dramatic increase in body size. But rather than making steady gains, infants and toddlers grow in little spurts. In one study, children who were followed over the first 21 months of life went for periods of 7 to 63 days with no growth, then added as much as half an inch in a 24-hour period! Almost always, parents described their babies as irritable and very hungry on the day before the spurt (Lampl,  1993 ; Lampl, Veldhuis, & Johnson,  1992 ).

One of the most obvious changes in infants’ appearance is their transformation into round, plump babies by the middle of the first year. This early rise in “baby fat,” which peaks at about 9 months, helps the small infant maintain a constant body temperature. In the second year, most toddlers slim down, a trend that continues into middle childhood (Fomon & Nelson,  2002 ). In contrast, muscle tissue increases very slowly during infancy and will not reach a peak until adolescence. Babies are not very muscular; their strength and physical coordination are limited.

Get solution to your nursing paper : Physical Development in Infancy and Toddlerhood

Individual and Group Differences

In infancy, girls are slightly shorter and lighter than boys, with a higher ratio of fat to muscle. These small sex differences persist throughout early and middle childhood and are greatly magnified at adolescence. Ethnic differences in body size are apparent as well. Grace was below the growth norms (height and weight averages for children her age). Early malnutrition contributed, but even after substantial catch-up, Grace—as is typical for Asian children—remained below North American norms. In contrast, Timmy is slightly above average, as African-American children tend to be (Bogin,  2001 ).

Children of the same age also differ in rate of physical growth; some make faster progress toward a mature body size than others. But current body size is not enough to tell us how quickly a child’s physical growth is moving along. Although Timmy is larger and heavier than Caitlin and Grace, he is not physically more mature. In a moment, you will see why.

The best estimate of a child’s physical maturity is skeletal age, a measure of bone development. It is determined by X-raying the long bones of the body to see the extent to which soft, pliable cartilage has hardened into bone, a gradual process that is completed in adolescence. When skeletal ages are examined, African-American children tend to be slightly ahead of Caucasian children at all ages, and girls are considerably ahead of boys. At birth, the sexes differ by about 4 to 6 weeks, a gap that widens over infancy and childhood (Tanner, Healy, & Cameron,  2001 ). This greater physical maturity may contribute to girls’ greater resistance to harmful environmental influences. As noted in  Chapter 2 , girls experience fewer developmental problems than boys and have lower infant and childhood mortality rates.

Changes in Body Proportions

As the child’s overall size increases, different parts of the body grow at different rates. Two growth patterns describe these changes. The first is the  cephalocaudal trend —from the Latin for “head to tail.” During the prenatal period, the head develops more rapidly than the lower part of the body. At birth, the head takes up one-fourth of total body length, the legs only one-third. Notice how, in  Figure 4.1 , the lower portion of the body catches up. By age 2, the head accounts for only one-fifth and the legs for nearly one-half of total body length.

In the second pattern, the  proximodistal trend , growth proceeds, literally, from “near to far”—from the center of the body outward. In the prenatal period, the head, chest, and trunk grow first, then the arms and legs, and finally the hands and feet. During infancy and childhood, the arms and legs continue to grow somewhat ahead of the hands and feet.

Get solution to your nursing paper : Physical Development in Infancy and Toddlerhood

At birth, the brain is nearer to its adult size than any other physical structure, and it continues to develop at an astounding pace throughout infancy and toddlerhood. We can best understand brain growth by looking at it from two vantage points: (1) the microscopic level of individual brain cells and (2) the larger level of the cerebral cortex, the most complex brain structure and the one responsible for the highly developed intelligence of our species.

Development of Neurons

The human brain has 100 to 200 billion  neurons , or nerve cells that store and transmit information, many of which have thousands of direct connections with other neurons. Unlike other body cells, neurons are not tightly packed together. Between them are tiny gaps, or  synapses , where fibers from different neurons come close together but do not touch (see  Figure 4.2 ). Neurons send messages to one another by releasing chemicals called  neurotransmitters , which cross the synapse.

FIGURE 4.2 Neurons and their connective fibers.

This photograph of several neurons, taken with the aid of a powerful microscope, shows the elaborate synaptic connections that form with neighboring cells.

FIGURE 4.3 Major milestones of brain development.

Formation of synapses is rapid during the first two years, especially in the auditory, visual, and language areas of the cerebral cortex. The prefrontal cortex undergoes more extended synaptic growth. In each area, overproduction of synapses is followed by synaptic pruning. The prefrontal cortex is among the last regions to attain adult levels of synaptic connections—in mid-to late adolescence. Myelination occurs at a dramatic pace during the first two years, more slowly through childhood, followed by an acceleration at adolescence and then a reduced pace in early adulthood. The multiple yellow lines indicate that the timing of myelination varies among different brain areas. For example, neural fibers myelinate over a longer period in the language areas, and especially in the prefrontal cortex, than in the visual and auditory areas.

(Adapted from Thompson & Nelson, 2001.)

The basic story of brain growth concerns how neurons develop and form this elaborate communication system.  Figure 4.3  summarizes major milestones of brain development. In the prenatal period, neurons are produced in the embryo’s primitive neural tube. From there, they migrate to form the major parts of the brain (see  Chapter 3 ,  page 82 ). Once neurons are in place, they differentiate, establishing their unique functions by extending their fibers to form synaptic connections with neighboring cells. During the first two years, neural fibers and synapses increase at an astounding pace (Huttenlocher,  2002 ; Moore, Persaud, & Torchia,  2013 ). A surprising aspect of brain growth is  programmed cell death , which makes space for these connective structures: As synapses form, many surrounding neurons die—20 to 80 percent, depending on the brain region (de Haan & Johnson,  2003 ; Stiles,  2008 ). Fortunately, during the prenatal period, the neural tube produces far more neurons than the brain will ever need.

As neurons form connections, stimulation becomes vital to their survival. Neurons that are stimulated by input from the surrounding environment continue to establish synapses, forming increasingly elaborate systems of communication that support more complex abilities. At first, stimulation results in a massive overabundance of synapses, many of which serve identical functions, thereby ensuring that the child will acquire the motor, cognitive, and social skills that our species needs to survive. Neurons that are seldom stimulated soon lose their synapses, in a process called  synaptic pruning  that returns neurons not needed at the moment to an uncommitted state so they can support future development. In all, about 40 percent of synapses are pruned during childhood and adolescence to reach the adult level (Webb, Monk, & Nelson,  2001 ). For this process to advance, appropriate stimulation of the child’s brain is vital during periods in which the formation of synapses is at its peak (Bryk & Fisher,  2012 ).

If few new neurons are produced after the prenatal period, what causes the dramatic increase in brain size during the first two years? About half the brain’s volume is made up of  glial cells , which are responsible for  myelination , the coating of neural fibers with an insulating fatty sheath (called myelin) that improves the efficiency of message transfer. Glial cells multiply rapidly from the fourth month of pregnancy through the second year of life—a process that continues at a slower pace through middle childhood and accelerates again in adolescence. Gains in neural fibers and myelination are responsible for the extraordinary gain in overall size of the brain—from nearly 30 percent of its adult weight at birth to 70 percent by age 2 (Johnson,  2011 ; Knickmeyer et al.,  2008 ).

Brain development can be compared to molding a “living sculpture.” First, neurons and synapses are overproduced. Then, cell death and synaptic pruning sculpt away excess building material to form the mature brain—a process jointly influenced by genetically programmed events and the child’s experiences. The resulting “sculpture” is a set of interconnected regions, each with specific functions—much like countries on a globe that communicate with one another (Johnston et al.,  2001 ). This “geography” of the brain permits researchers to study its developing organization and the activity of its regions using neurobiological methods.