Chapter 4: Growth and Health


  • Growth follows two distinct trends
  • Cephalocaudal - Head to tail
  • Proximodistal - Close in to farther out
  • Head and trunk grow faster than the legs in infants
  • Secular growth trends- physical development from one generation to the next

Mechanisms of Physical Growth

  • Sleep
  • Infants have more time in the day of sleep than awake
  • The amount of time that children spend asleep drops gradually from 12 hours at age 3 to 10 hours at age 7 and 8 hours at age 12
  • Growth hormone- 80 percent is secreted by the pituitary gland while children and adolescents sleep. It is essential to growth.
  • Sleep loss can be a particular problem for adolescents, less sleep, harmful and more symptoms for depression and lower self esteem.
  • Nutrition
  • Growth requires much energy and so must consume more calories
  • Breastfeeding- antibodies to decrease the risk of allergies, the right amount of nutrients and calories for the infant

The Adolescent Growth Spurt and Puberty

Puberty - The adolescent growth spurt and sexual maturation

  • 2-year growth spurt between girls and boys

Osteoporosis - a disease in which a person’s bones become thin and brittle and, as a consequence, sometimes break. It can strike at any age but people above 50 are at greater risk. More women than men suffer this form of bone loss because after menopause the ovaries no longer produce as much estrogen, which guards against bone deterioration.

  • Sexual Maturation
  • Primary sex characteristics- maturation of organs that are directly involved in reproduction.
  • Secondary sex characteristics- physical signs of maturity that are not linked directly to the reproductive organs.

Menarche - The onset of menstruation- at around age 13

Spermarche - The first spontaneous ejaculation of sperm laden fluid

  • Mechanisms of Maturation
  • The pituitary gland in the brain causes the many physical changes in puberty.


  • Malnutrition during rapid periods of growth apparently damages the brain, affecting a child’s intelligence and ability to pay attention and learn.
  • Short- Term Hunger- When children don’t eat breakfast, they often have difficulty paying attention or remembering in school.

Eating Disorders- Anorexia and Bulimia

  • Anorexia nervosa is a disorder marked by a persistent refusal to eat and an irrational fear of being overweight.
  • Individuals with bulimia nervosa alternate between binge eating, when they eat uncontrollably, and purging—through self-induced vomiting or with laxatives.
  • Body dysmorphic disorder individuals are not satisfied with their body shape or the shape of a particular part of the body, and perceived muscularity is often the focus. More in Boys.


  • BMI - body mass index- an adjusted ratio of weight to height.
  • Given the health risks associated with obesity, it is unfortunate that many parents and children seem to underestimate their own weight and think them¬ selves a normal weight when in fact they are overweight or even obese.
  • Basal metabolic rate - the speed at which the body consumes calories.
  • Heredity plays an important role in juvenile obesity.
  • Environment is also influential - Cultural norms, television advertising, external ques reinforced by parents.


  • The five condition leading killers of young children worldwide-
  • Pneumonia
  • Diarrhea
  • Measles
  • Malaria
  • Malnutrition

Organization of the Mature Brain

Neuron - The basic unit of the brain and the rest of the nervous system, a cell that specializes in receiving and transmitting information.

Cell body - at the center of the neuron, contains the basic biological machinery that keeps the neuron alive.

Dendrite - The receiving end of the neuron, looks like a tree with many branches.

Axon - the slender elongated structure at the other end of the cell body, which sends information to other neurons.

Myelin - raps the axon, a fatty sheath that allows it to transmit information more rapidly.

Terminal buttons - at the end of the axon, small knobs which release neurotransmitters, chemicals that carry information to nearby neurons.

Synapse - The gap between one neuron and the next.

Cerebral cortex - wrinkled surface of the brain, made up of 10 billion neurons, it regulates many of the functions that we think of as distinctly human.

Hemispheres - Left and right halves

  • Producing and understanding language - Left hemisphere
  • Artistic and musical abilities, perception of spatial relationships and face and emotion recognition - Right hemisphere

Corpus callosum - links the left and right hemispheres by millions of axons in a thick bundle.

Frontal cortex - personality and ability to make and carry out plans.

The Developing Brain

  • Emerging Brain Structures
  • Neural plate - a flat structure formed at roughly 3 weeks after conception.
  • At 4 weeks the neural plate folds to form a tube that ultimately becomes the brain and the spinal cord
  • When the ends of the tube fuse shut, neurons are produced in one small region of the neural tube. Production of neurons begins about 10 weeks after conception, and by 28 weeks the developing brain has virtually all it will ever have.
  • The brain is built in layers- from innermost layer to outermost layer.
  • At 4 months, axons begin to acquire myelin to speed up transmission.
  • More myelin- improves coordination and reaction time.
  • In the months after birth, the brain grows rapidly. Axons and dendrites grow longer, and, like a maturing tree, dendrites quickly sprout new limbs. As the number of dendrites increases, so does the number of synapses, reaching a peak number at about the first birthday.
  • Synaptic pruning - decrease of synapses, synapses that are active are preserved, bit those that aren’t are eliminated.
  • Structure and Functions
  • For many years, the only clues to specialization came from children who had suffered brain injury.
  • Other ways to study brain development
  • Electro-encephalography (EEG)- measuring electric activity from electrodes on the scalp.
  • Functional magnetic resonance imaging (fMRI)- uses magnetic fields to track blood flow in the brain.

Brain specializations as children develop

  • Specialization occurs early in development- certain areas of the brain specialize in different functions.
  • Specialization takes two specific forms- First, regions that are active during cognitive processing become more focused and less diffuse. Second, kinds of stimuli that trigger brain activity shift from being general to being specific.
  • Different brain systems specialize at different rates- brain regions involving basic sensory and perceptual processes specialize well before those regions necessary for higher-order processes.
  • Successful specialization requires stimulation from the environment
  • Environmental input influences experience-expectant growth - Over the course of evolution, human infants have typically been exposed to some forms of stimulation that are used to adjust brain wiring, strengthening some circuits and eliminating others.
  • Experience-dependent growth denotes changes in the brain that are not linked to specific points in development and that vary across individuals and across cultures.
  • The immature brain’s lack of specialization confers a benefit- greater plasticity. Young children often recover more skills after brain injury than older children and adults, apparently because functions are more easily reassigned in the young brain

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