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Chapter 6

PSYC 2450 Chapter Notes - Chapter 6: Skeletal Muscle, Muscular Development, Myocyte

Course Code
PSYC 2450

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Chapter 6: Physical Development (164-204)
Changes in Height and Weight
Babies grow rapidly during first 2 years (x2 weight by 4-6 months and x3 [9.5-10kg] by end of
first year)
Growth is uneven in infancy (remain the same length for days and weeks)
By age of 2 toddlers already half of their eventual height, x4 birth weight
From age of 2 till puberty kids gain 5-8cm in height and 3kg in weight each year
After large growth spurt, only small increases
Changes in Body Proportion
Newborns head is already 70% of its eventual adult size and represents ¼ of total body length
Cephalocaudal Development: sequence of physical maturation and growth that proceeds from
head (cephalic region) to tail (caudal region)
Trunk grows fastest during first year
At age 1 child’s head is only 20% of total
body length
From year 1-puberty (adolescent growth
spurt) legs grow rapidly, more than 60% of
increase in height
Proximodistal Development: sequence of physical maturation and growth that proceeds from
the centre of the body (proximal region) to the extremities (distal region)
During prenatal development, the chest and internal organs form first, followed by arms and
legs then hands and feet. (166)
Reason teenagers appear clumsy is because hands and feet are tool large for rest of bodies
Skeletal Development
During prenatal development, soft cartilage skeletal structures are initially there, then they
gradually harden into (ossify) into bony material.
Nearly all bones are source of rbc at birth
At birth, infant’s bones are soft, pliable and hard to break. Because of this its hard for a baby to
sit of straight because they are too flexible
Neonates skull consists of several soft spots (fontanelles)
that gradually filled in by minerals to form a single skull by
age of 2
Sutures allow the skull the fully expand as brain grows
Wrist, ankles, feet and hands develop more bones as child matures. Wrist and hand bones of a 1
year old are less interconnected than the corresponding skeletal equipment of adolescent
Method of detecting a child’s level of physical maturation is to x-ray the wrist and hand

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Skeletal Development (cont’d)
Skeletal Age: measure of physical maturation based on child’s level of skeletal development
Researchers found that girls tend to mature faster in their skeletal development (4-6 weeks
Skulls and hands mature first, whereas the leg bones continue to develop till mid-late teens
Skeletal development is complete by the age of 18 (the widths and thickness of skull, leg bones
and hands increase slightly throughout life)
Muscular Development
Neonates are born with all the muscle fibre they’ll ever have
At birth muscle tissue is 35% water and accounts for approx. 18-24% of baby’s body weight
Protein and salt in cellular fluid of the muscle tissue allows muscle fibres to grow
Muscular development proceeds in the cephalocaudal and
Proximodistal directions, w/ muscles in head and neck
maturing before those in trunk and limbs
Maturation of muscle tissue occurs gradually then speeds
up in early adolescence
Consequence of this muscular growth spurt is that both
sexes become stronger (more dramatic in boys)
By mid 20s, skeletal muscle accounts for 40% of body
weight of an avg male, compared with 24% for the avg
Variation in Physical Development
Brain and head grow much faster and quicker to reach adult
Genitals and other reproductive organs grow slowly
throughout childhood and increase in adolescence
Lymph levels (immune system to help fight off diseases etc.)
overshoot adult levels then decrease during adolescence
Individual Variations
Development of body systems is an uneven/asynchronous
process, hence there is still a sizable individual variation in
rates ppl grow
Individual maturation rate differences also result in other areas of
development such as cognition
Cultural Variations
People from Asia, South America, and Africa tend to be smaller than
North Americans, North Europeans and Australians
Asian and African American children tend to mature faster than
European American and European children.
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