PSYC 2450 Chapter 6: Chapter 6

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Developmental Psychology Chapter 6
Changes in Height and Weight
In the first few months of life, babies gain over 28g each day and 2.5 cm each
month
Babies grow very rapidly during the first 2 years, often doubling their birth weight
by 4-6 months of age and tripling it by the end of the first year
By age 2, toddlers are already half their eventual adult height and have
quadrupled their birth weight to about 12-14 kg
From age 2 until puberty, children gain about 5-8 cm in height and about 3 kg in
weight each year
During middle childhood, children may seem to grow very little; over the course
of an entire year, 5 cm and 3 kg gained are hard to detect on a child who stands
1.2-1.4 m tall and weighs 27-36 jg
Physical growth and development are obvious at puberty, when adolescents
enter a two to three-year growth spurt, during which they may post an annual
gain of about 4.5 to 7 kg and 5 to 10 cm in height
There are typically small increases in height until full adult stature is attained in
the mid to late teens
Changes in Body Proportions
The newborn’s head is already 70% of its eventual adult size and represents one
quarter of total body length, the same fraction as the legs
Development proceeds in a cephalocaudal (head downward) direction
Cephalocaudal development: a sequence of physical maturation and growth that
proceeds from the head (cephalic region) to the tail (or caudal region)
the trunk grows fastest during the first year
at 1 year of age, a child’s head now accounts for only 20% of total body length
from the child’s first birthday until the adolescent growth spurt, the legs grow
rapidly, accounting for more than 60% of the increase in height
during adolescence, the trunk once again becomes the fastest-growing segment
of the body, although the legs are also growing rapidly at this time
when we reach our eventual adult height, our legs will account for 50% of total
height and our heads only 12%
while children grow upward, they are also growing outward according to a
proximodistal (centre outward) direction
Proximodistal development: a sequence of physical maturation and growth that
proceeds from the centre of the body (the proximal region) to the extremities
(distal regions)
The chest and internal organs form first, then arms and legs, then the hands and
feet
Throughout infancy and childhood, the arms and legs grow faster than the hands
and feet,
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However, this centre-outward growth pattern reverses just before puberty, when
the hands and feet begin to grow rapidly and become the first body parts to reach
adult proportions, followed by the arms and legs and finally the trunk
Skeletal Development
The skeletal structures that form during the prenatal period are initially soft
cartilage that will gradually ossify (harden) into bony material
At birth, nearly all of the bones are a source of blood cells
During postnatal development, production of blood cells is limited to few specific
bones
Neonates cannot sit up because their bones are too small and too flexible
The neonate’s skull consists of several soft bones that can be compressed to
allow the child to pass through the cervix and the birth canal
The skull bones are separated by 6 soft spots, or fontanelles, that are filled in by
minerals to form a single skull by age 2, with pliable points at seams where skull
bones join
These seams, or sutures, allow the skull to expand as the brain grows larger
Other parts of the body namely, the ankles and feet, wrists, and hands-
develop more bones as the child matures
One method of estimating a child’s level of physical maturation is to X-ray wrist &
hand
o The X-ray shows the number of bones and the extent of their ossification,
which is then interpretable as a skeletal age
o Skeletal age: a measure of physical maturation based on the child’s level
of skeletal development
Girls mature faster than boys
At birth, girls are only 4-6 weeks ahead of boys in their level of skeletal
development: but by age 12 the gender difference has widened to two full years
Skull and hands mature first, whereas the leg bones develop until the mid to late
teens
Skeletal development is complete by age 18, although the widths of the skull, leg
bones, and hands increase slightly throughout life
Muscular Development
Neonates are born with all the muscle fibres they will ever have
At birth, muscle tissue is 35% water, and it accounts for no more than 18-24% of
a baby’s body weight
Muscular development proceeds in a cephalocaudal and proximodistal
directions, with muscles in the head and neck maturing before those in the trunk
and limbs
Maturation of muscle tissue occurs very gradually over childhood and then
accelerates during early adolescence
Increases in both muscle mass and physical strength are more dramatic for boys
By the mid-20’s, skeletal muscle accounts for 40% of the body weight of an
average male, compared with 24% for the average female
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Variations in Physical Development
Growth of the lymph tissues which make up part of the immune system and
help children fight off infections actually overshoots adult levels late in
childhood, before declining rapidly in adolescence
Individual Variations
Development of body systems are an uneven process
Warren Eaton and Kathryn Ritchot at the University of Malibu found that faster
processing speed was found in early maturers, especially among boys
Cultural Variations
People from Asia, South America, and Africa tend to be smaller than North
Americans, Northern Europeans, and Australians
Asian and African American children tend to mature faster than European
American and European children
Asynchronies in the maturation of different body systems are built into our
species’ heredity – that is, the common maturational program that all humans
share
Development of the brain
The last 3 prenatal months and the first two years after birth have been termed
the period of the brain growth spurt because more than half of an individual’s
adult brain weight is added at this time
Brain growth spurt: the period between the seventh prenatal month and 2 years
of age when more than half of the child’s eventual brain weight is added
Neural Development and Plasticity
The human brain and nervous system consist of more than a trillion highly
specialized cells that work together to transmit electrical and chemical signals
across many trillions of synapses, or connective spaces between the cells
o Synapse: connective space (juncture) between one nerve cell(neuron) and
another
Neurons are the basic unit of the brain and nervous system the cells that
receive and transmit neural impulses
o Neurons are produced in the neural tube of the developing embryo
o From there, they migrate along pathways laid down by a network of
guiding cells to form the major parts of the brain
100-200 billion of neurons already formed by the end of the 2nd trimester of
pregnancy
scientists have established the formation of new neurons in the hippocampus (an
area of the brain important to learning and memory) occurs throughout life
what accounts for the brain growth spurt?
o The development of a second type of nerve cells, called a glia, which
nourish the neurons and eventually encase them in insulating sheaths of a
waxy substance called myelin
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