Chapter 6 - Physical Development: The Brain, Body, Motor Skills, and Sexual
Changes in Height and Weight
- Grow very rapidly during first 2 years, doubling birth weight by 4 to 6 months and tripling it
by the end of the first year.
- By age 2, toddlers are half of their eventual adult height and have quadrupled their birth
- From age 2 until puberty, children gain about 5 to 8 cm in height and about 3 kg each year.
- Between ages 6 and 11, children seem to grow very little
Development proceeds in a cephalocaudal (head downward) direction.
Children grow outward according to proximodistal (Centre outward) direction. (Organs and
chest first, followed by arms, legs, hands, feet)
- Skeletal structures during prenatal period are soft cartilage that hardens into bony material
- At birth, nearly all bones are a source of blood cells.
- Postnatal development production of blood cells limited to a few specific bones
- At birth, the bones are soft, pliable and difficult to break
- Reason why they can’t stand or sit up bones are too small and flexible.
- Skull bones separated by 6 soft spots at birth and by age 2, they are filled in by minerals to
form a single skull.
- Skeletal Age: A measure of physical maturation based on the child’s level of skeletal
- Infants born with all the muscle fibers they will ever have
- At birth, muscle tissue is 35% water, and its 18% to 24% baby’s weight.
- Proceeds in cephalocaudal and proximodistal directions with muscles in the head and neck
maturing before limbs.
- People from Asia, South America, and Africa are smaller than Americans and Europeans but
they are more mature.
Development of the Brain
- 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
- Brain and nervous system cells work by transmitting electrical and chemical signals across
- Synapses: The connective space (juncture) between one nerve cell (neuron) and another.
- Neuron: Nerve cells receive and transmit neural impulses.
- Neurons are produced in the neural tube of the embryo
- Glia: Nerve cells that nourish neurons and encase them in insulating sheaths of myelin.
1 - Synaptogenesis: Formation of connections (synapses) among neurons.
- Occurs rapidly during the brain growth spurt.
- Plasticity: Capacity or change; a developmental state that has the potential to be shaped by
experience. Cells highly responsive to the effects of experience.
- Surviving neurons that are stimulated less often lose their synapses (synaptic pruning) and
stand in reserve to compensate for brain injuries or to support new skills.
The Role of Experience
- Riesen: infant chimpanzees reared in the dark for period of up to 16 months. Dark-reared
chimpanzees experienced decreased activity of the retina and the neurons that make up the
optic nerve. Decrease was reversible if exposure was less than 7 months but if it was more
than a year, it could result in complete blindness.
Brain Differentiation and Growth
- At birth, lower (subcortical) brain centers, which control consciousness, inborn reflexes,
digestion, respiration, and elimination are the most developed.
- Around that area is the cerebrum and cerebral cortex, areas most implicated in bodily
movements, perception, learning, thinking, and language.
- First areas of cerebrum to mature are the primary motor areas (waving arms), and the
primary sensory areas (vision, hearing, smelling, tasting).
- As cells grow, glia begins to produce a waxy substance called myelin, which forms a sheath
around neurons. Acts like an insulator to speed the transmission of neural impulses, allowing
the brain to communicate better.
- Myelination: The process by which neurons are enclosed in waxy myelin sheaths that will
facilitate the transmission of neural impulses.
- Reticular formation and frontal cortex, concentration on a subject for a long time, is not
myelinated until puberty.
- Highest brain center is the cerebrum, consists of two halves connected by a band of fibers
called corpus callosum.
- Each half is covered by a cerebral cortex, outer layer of gray matter that controls sensory
and motor processes, perception, and intellectual functioning.
- Left half controls right side of the body, and speech, hearing, verbal memory, decision-
making, language processing, expression of positive emotions.
- Right half controls the left side and processing visual, spatial information, nonlinguistic
sounds, music, tactile (touch) sensations, and expressing negative emotions.
- Brain is a lateralized organ.
- Cerebral laterization involves a preference for using one hand
See picture 5.6
See table 5.1
2 - Motor development proceeds in cephalocaudal (head downward) direction head, neck,
and upper body before legs and lower body.
- Motor development proceeds in proximodistal (center-outward) direction trunk, shoulders
before hands and fingers.
- Describes motor development as the unfolding of a genetically programmed sequence of
events, where the nerves and muscles mature in a downward and outward direction.
- As a result, children grain more control over the lower and peripheral parts of their bodies
displaying motor skills as seen in table 5.1
- Comes from cross-cultural research
o Practice had little impact, infants from around the world follow same sequence
Experiential (Practice) Viewpoint
- Believes that opportunities to practice motor skills are also important.
- Concludes that maturation is necessary but not sufficient.
- Practice makes perfect
Dynamical Systems Theory
- Differ from earlier theorists in two ways
o They do not view motor skills as genetically programmed responses that simply “unfold” as
said by maturation and opportunities to practice.
o Instead they view each new skill as a construction that emerges as infants actively
reorganize existing motor capabilities into new and more complex action systems.
o Said that visual orientation, going after something they want, motivates the infant to
approach interesting stimuli.
o Represents an active and intricate reorganization of several existing capabilities that is
undertaken by a curious, active infant who has a particular goal in mind.
Fine Motor Development
- Voluntary Reaching
o 3 months of age or older, infants try to grasp onto things
o Good at reaching for things that can either only hear or see
o 5 months, infants proficient at reaching for and touching stationary illuminated objects or
glowing objects that move in the dark
o Proprioceptive information: Sensory information from the muscles, tendons, and joints
that help one to locate the position of one’s bod