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Child Development - A Thematic Approach
, Fifth Edition
Danuta Bukatko - College of the Holy Cross
Marvin W. Daehler - University of Massachusetts, Amherst
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| | Chapter Outline
Chapter 5:
Brain, Motor Skill, and Physical Development
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The brain and nervous system
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The developing brain
Our knowledge of the brain and brain structure has increased tremendously over the past decade due in no small part to technological advances. Cognitive
neuroscientists utilize a number of different procedures including positron
emission tomography (PET), functional magnetic resource imaging (fMRI), and
event-related potentials (ERP) to determine which regions of the brain are functioning during the processing
of various kinds of information.
The brain grows rapidly during the prenatal period and continues to grow
after birth, though at a slower rate. Different brain areas grow at different rates; the brainstem and midbrain are almost complete at birth,
while the cerebral cortex continues to develop postnatally. The brain consists
of neurons and glial cells, which outnumber neurons by a factor of ten. Parts of many neurons become surrounded by myelin, a sheath of fatty material that insulates and speeds up neural impulses.
Neuron proliferation, neuron migration, and neuron differentiation are all
part of prenatal brain development. After birth, additional brain development
is due largely to neuron differentiation, which increases the number of connections
between neurons. However, recent research has revealed that at least in some
regions even neuron production can take place well into adulthood. Both the
number of neurons and the density of their synapses with other neurons are probably greater in infancy
in many regions of the brain than at other times in development. -
Plasticity in brain development
Certain brain areas and the individual neurons within these areas possess plasticity, the ability of a brain structure to replace the functions normally controlled
by other brain areas should these other areas become damaged. Some neurons are sensitive
to experience-expectant information, such as in the development of depth
or pattern vision in many animals. Other neurons are sensitive to experience-dependent
information. -
Brain lateralization
The cerebral cortex is divided into right and left hemispheres. In general,
each hemisphere has specialized functions. The process by which one hemisphere
dominates the other is called lateralization. For example, in most right-handed people the left hemisphere is especially
involved in language, while the right hemisphere is involved in spatial processing.
Studies suggest that infants display behaviors that indicate lateralization
at birth; however, lateralization may increase later in development.
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Motor skill development
Motor development follows cephalocaudal and proximodistal patterns. In addition,
differentiation and integration of motor abilities occur with development.-
The first actions: reflexes
The earliest movements of the newborn are reflexes, involuntary responses to environmental stimuli such as touch, sound, and
light. Primitive reflexes are necessary for survival and include reflexes that provide
nourishment, such as rooting and sucking. Postural reflexes maintain body
orientation and include stepping and body righting.
Research Applied to Parenting: Helping to Reduce Sudden Infant Death Syndrome
The ability to modify reflexes and integrate them with voluntary motor skills
is an important developmental process. Sudden infant death syndrome (SIDS), the abrupt, unexplained death of an otherwise healthy infant, may be a result of an unsuccessful integration of reflexive and voluntary
control of breathing. Although no single cause has been identified, several
factors have been correlated with SIDS. The steps parents can take to help
reduce the likelihood of SIDS include placing the infant on his or her back or side to sleep, eliminating
exposure to cigarette smoke, providing firm bedding, and avoiding overheating.
Some researchers also suggest that having the infant sleep in the same room
as the caregiver during the first few months of development also helps reduce the risk of SIDS. |
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Motor milestones
During the first year of life, infants exhibit rhythmical stereotypes, repeated sequences of movements that do not appear to be goal directed but may be integrated into later voluntary behaviors.
Directed, voluntary behaviors gradually emerge in the first year. Some of
these behaviors can be described as motor milestones because they provide
the infant with new ways to interact with the environment. Among these are the ability to maintain postural
control, and locomotion, including the ability to walk independently. Learning
about the many objects in the world improves when progress in eye-hand coordination
and preheating behavior develops into the ability to control objects manually. -
Motor skills in preschool and later-childhood years
Differentiation and integration of motor and sensory skills continue to
develop into the preschool and later-childhood years. Toddlers and young preschoolers engage
primarily in large-muscle activity. Older preschoolers engage in a greater
number of small-muscle activities such as coloring, drawing, and cutting.
Throughout childhood, children perform motor skills more quickly and efficiently, providing them with increasing
competence in their interactions with the environment. -
Determinants of motor development
Evidence consistent with a maturational view of motor development is suggested by the tendency in all children
to undergo predictable and orderly patterns of motor development. Even developmentally
disabled babies achieve milestones in the same sequence as normal babies,
although somewhat more slowly. Greater concordance in motor skills with increasing genetic similarity
supports a genetic influence on motor development.
The serious developmental delays seen in institutionalized children who are
severely deprived of experiences with motor activity demonstrate that environmental
factors are also crucial for proper motor development. Some types of experiences
may promote the acquisition of motor milestones. However, infants engaged in a range of
physical activity often receive a sufficient variety of experiences to allow
them to assemble the multiple processes that underlie the acquisition of
complex motor behavior. -
Cross-cultural differences
Cross-cultural differences in the onset of motor milestones may indicate
genetic differences as the source of cultural dissimilarities in motor development.
However, differences in child rearing across cultures cannot be ruled out as a contributor to such cultural
dissimilarity.
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Body growth and development
Physical growth and development of motor skills influence cognitive, social,
and other dimensions of development. Cognitive and social factors, such as how an individual
is perceived by others, can in turn influence the physical growth and development
of motor skills. Growth refers specifically to the increase in physical size
of the body. Development refers to the orderly patterns and levels of functioning associated
with growth.-
Norms of growth
To determine whether rate of growth in an individual is proceeding satisfactorily,
physical characteristics such as weight and height are measured quantitatively
in a sample of the population at different ages to establish norms. Such normative data indicate that while males and females grow at a similar
rate in infancy and childhood, an adolescent growth spurt occurs in girls about two years earlier than it occurs
in boys. -
Directionalities of growth
The rate of growth for various body systems differs and depends on the functional
importance of the particular system. Thus, the brain grows rapidly early in infancy, whereas
maturity of the reproductive system is delayed until adolescence. The pattern
of development for individual systems of the body is often cephalocaudal--parts of the body near the head grow more rapidly than parts more distant from the head--or proximodistal--parts of the body near the middle develop before those near the periphery.
Considerable variability occurs in the rate of physical growth and development
among individuals within a group as well as among ethnic and cultural groups. -
Determinants of body growth and development
Genetic influences on physical growth are strongly implied by similarities
in height and body proportion among family members and significant differences among cultural and racial groups.
Many researchers believe the brain contains a growth center, a genetically
established program or template that monitors and compares expected and actual
rate and levels of growth for the individual. Support for this idea comes from catch-up growth and lagging-down growth, which occur when factors interfere with normal growth. This brain structure
regulates the pituitary gland to release hormones necessary for growth.
The effects of the nutritional environment on growth can be positive, such as when diet
is sufficient or when supplements are added to increase weight in children
at risk for malnourishment, or negative, as in the case of miasmas and kwashiorkor,
forms of severe malnutrition. Inadequate or abusive care giving can lead to retardation of physical
growth as indicated by failure to thrive. The powerful influence of the environment on maturation is also evident when
examining secular trends, consistent patterns of change that occur over generations when the environment changes. -
The social-emotional consequences of body growth
When no organic reason is found, failure to thrive is the term applied to children whose growth or weight fall below the third percentile for children of the same age. Parental
factors, such as abuse or neglect, may contribute to this syndrome. Increased
knowledge of nutrition has also resulted in secular trends, in that the average height of people has steadily increased over several generations.
Social emotional factors also influence people's reactions towards children based on their height and weight. People's perceptions of one another are often influenced by observable physical
characteristics. Taller boys, for example, are seen as more competent than shorter boys. Society's stereotypical attitudes about height have led some parents to seek human
growth hormone treatment to increase their children's height, a procedure that raises many ethical questions.
Despite the negative attitudes toward people with excess weight, obesity has increased substantially in recent decades.
An increase in the time spent in sedentary activity, limited physical activity,
and shifts to higher-calorie diets all contribute to the increase in obesity
in children. Genetic predispositions for obesity may interact with the environment so that obese
children less effectively monitor their calorie intake.
Atypical Development: Dieting and Eating Disorders
Many people, especially girls, report dissatisfaction with their weight and report efforts to diet. The perceived social and
cultural pressures to maintain an ideal weight may also contribute to eating
disorders such as anorexia nervosa and bulimia nervosa. These eating disorders
appear to be increasing in Western societies. Cultural influences appear to be a contributing factor
especially for bulimia nervosa. Both disorders can have serious health consequences. |
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Physical maturity
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Defining maturity
The most reliable measure of growth is skeletal maturity, which is determined by x-rays of the size, shape, and position of bones and
measures the extent to which ossification of cartilage into bony tissue has
occurred. Other observable indicators of increasing maturity are associated with puberty, such as spermarche in males and menarche in females. Gonad tropic hormones released by the pituitary gland contribute
to the production of sperm and elevate the production of testosterone in boys. They also regulate the menstrual cycle and stimulate the
production of estrogen and progesterone in girls. But indexes of sexual maturity,
as in the case of physical size, are quite variable both within and among
individuals. -
Early versus late maturity
Most teenagers are concerned about their changing bodies and their attractiveness.
Teenagers' attitudes toward their physical appearance depend on many factors, including
maturity, sex, degree of preparedness for the physical changes that occur at puberty, and other
sociocultural factors. In females, knowledge of the changes that occur at
puberty decreases the likelihood of viewing menarche as a negative event.
Early maturity enhances satisfaction with appearance in males but is associated with a more mixed outcome
for females, especially if older peers are among their friends. -
Sexual behavior
With increasing numbers of teenagers engaging in sexual behavior at younger ages, concerns about the factors, such as parental interaction
and neighborhood contexts, that contribute to this behavior are increasing.
In addition, the moral and ethical issues surrounding adolescent sexual behavior
have important health and social consequences, including sexually transmitted diseases and
teenage pregnancy.
Controversy: What Should the Content Be in Sex Education Programs?
Most adults believe sex education should be taught in school. However, the content of the curriculum is often debated. Tests of the effectiveness of
sex education have yielded mixed results. However, programs that emphasize
addressing the many tasks that confront teenagers in addition to their concerns
about sexual activity may be among the most effective in promoting responsible behavior. |
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