PSYC 2450 Chapter Notes -Muscular Development, Skeletal Muscle, Neural Tube
PSYC 2450- CH 6: Physical Development of the Brain, Body, Motor Skills
& Sexual Development
An Overview of Maturation & Growth
Changes in Height & Weight
•Height & weight increase rapidly in the first two years- but it is very uneven.
•By age 2 toddlers are half their eventual height & have quadrupled their birth
•Age 2 until puberty, children gain 5-8 cm in height & 3kg in weight every year
•Two to 3 year growth spurt at adolescence.
Changes in Body Proportions
•A newborn’s head is 70% of it’s eventual adult size & makes up ¼ of their total
Cephalocaudal Development- a sequence of physical maturation and growth that
proceeds from the head (cephalic region) to the tail (caudal region).
Proximodistal Development- a sequence of physical maturation and growth that
proceeds from the centre of the body (the proximal region) to the extremities (distal
•Pattern reverse before puberty- hands & feet are first to adult size, followed by
limbs & then the trunk.
•At birth an infant’s bones are soft & nearly all the bones are a source of blood
cells- reason why they can’t sit up
•Skeletal & muscular development parallel the changes occurring in height &
•The skull is separated by six soft spots (fontanelles) which are filled in by
minerals to form single skull by 2
Skeletal Age- a measure of physical maturation based on the child’s level of skeletal
•Skeletal development is done by 18, but the thickness increases slightly
•Born with all the muscles we will ever have
•At birth it is 35% water but grows as the cellular fluid in muscle tissues is
bolstered by protein & salt
•Grows slowly in childhood & accelerates in adolescence
•By Mid 20’s skeletal muscle accounts for 40% of boys’ body weight & only 24%
Variations in Physical Development
•Physical growth is uneven (asynchronous)
oBrain, reproductive system & lymph tissues mature at diff rates.
oSizeable individual & cultural differences in development.
Development of the Brain
•Increases from 25% of eventual weight to 75% of eventual weight by 2.
Brain Growth Spurt- the period between the 7th prenatal month and 2 years of age
where more than half of the child’s eventual brain weight is added.
Neural Development & Plasticity
Synapses- the connective space between one nerve cell (neuron) and another.
Neurons- nerve cells that receive and transmit neural impulses
•Produced in the neural tube of developing embryos & migrate along pathways
laid out by guiding cells to form major parts of the brain.
•Formation of new neurons in the hippocampus occurs throughout life
Glia- nerve cells that nourish neurons and encase them in insulating sheaths of myelin
•Major contributor to brain development
•Many more neurons & synapses are created than are ever needed- those that are
unused disappear (pruning) and those that are used are strengthened.
•Individual neurons have the potential to serve any function, but it depends where
they end up.
Synaptogenesis- formation of connections (synapses) among neurons.
Plasticity- capacity for change; a developmental state that has the potential to be shaped
•Brain shows a lot of this up until puberty
•Highest brain centre (cerebellum) consists of two hemispheres separated by the
Myenilization- the process by which neurons are enclosed in waxy myelin sheaths that
facilitate the transmission of neural impulses.
Cerebrum- the highest brain centre; includes both hemispheres of the brain and the
fibres that connect them.
Corpus Callosum- the bundle of neural fibres that connect the two hemispheres of the
brain and transmit information from one hemisphere to the other.
Cerebral Cortex- the outer layer of the brain’s cerebrum, which is involved in voluntary
body movements, perception & higher intellectual functions such as learning, thinking
Cerebral Lateralization- the specialization of brain functions in the left and right
•Now thought that brain lateralization starts prenatally and is underway during
birth- but not completely specialized, children come to rely heavily on one
hemisphere or the other to perform each function
•Like the physical strucutres, motor development proceeds in cephalocaudal &
•Infants gain control over their heads, necks and upper arms before their hands,
feed and legs.
Maturational viewpoint- unfolding of genetically programmed development where nerves
& muscles mature in a downward & outward direction- shown by cross-cultural research
Experiential (practice) hypothesis- no one denies maturation plays a part, but experience
plays a large roll. If children don’t have the opportunity to practice the skills they gain
from maturation, they will not keep them.
Dynamical Systems Theory- a theory that views motor sills as active reorganizations of
previously mastered capabilities undertaken to find more effective ways of exploring the
environment or satisfying other objectives.
•Doesn’t see motor skills as genetically programmed
•View each new skill as a “construction” as infants “actively reorganize” their
•Fine motor skills increase dramatically in the first year
oPre-reaching are uncoordinated swipes at objects in their vision, they
change into voluntary reaching
oVoluntary reaching begins at 3 months of age and babies develop their
own unique pathways (some start too hard, and learn to grasp softer and
Proprioceptive Information- sensory info from the muscles, tendons, and joints that
help one to locate the position of one’s body (or body parts) in space.
Ulnar Grasp- an early manipulatory skill in which an infant grasps objects by pressing
the fingers against the palm
Pincer Grasp- a grasp in which the thumb is used in opposition to the fingers, enabling
an infant to become more dexterous at lifting and fondling objects
•Develops in the second half of the first year
Puberty: The Physical Transition from Child to Adult
Adolescent Growth Spurt- the rapid increase inn physical growth that marks the
beginning of adolescence
Puberty- the point at which a person reaches sexual maturity and is physical capable of
fathering or conceiving a child.
•Girls typically enter the growth spurt by 10 ½ and reach a peak at 12, and boys
typically start at 13 & peak at 14
Menarche- the first occurrence of menstruation (spermarche is the equivalent for boys-
•The secular trend refers to the fact people are reaching puberty earlier than before
oDue to improved nutrition & healthcare
oPeople are also growing taller & heavier than before
Causes & Correlates of Physical Development
Thyroxine- a hormone produced by the thyroid gland; essential for normal growth of the
brain and the body