Infants and Children in Context. Tara L. Kuther

in the United States, which can mask the health dangers of once-common infections. With little to no experience with vaccine-preventable diseases, young parents may be unaware of the threat these diseases pose or the need to seek protection.

      Another reason is that many families in the United States do not have access to the health care they need. Children in families with incomes below the poverty level are less likely to receive the combined series vaccination (Child Trends, 2015). Many parents are unaware that children from low-income families who do not have medical insurance can receive vaccinations through the federal Vaccines for Children program, begun in 1994.

      Some parents choose not to vaccinate their children because of the common misconception that vaccines are linked with autism (Salmon, Dudley, Glanz, & Omer, 2015). Extensive research indicates that there is no association between vaccination and autism (Modabbernia, Velthorst, & Reichenberg, 2017; Taylor, Swerdfeger, & Eslick, 2014). Instead, children tend to receive vaccines at the age when some chronic illnesses and developmental disorders—such as autism—tend to emerge, but this correlation is not indicative of a cause-and-effect relationship. (Recall from Chapter 1 that correlational research documents phenomena that occur together but cannot demonstrate causation.) As we discuss later in this chapter, although specific causes of autism spectrum disorders have yet to be fully identified, these disorders appear to have a strong genetic component (Lee & McGrath, 2015; Waltes et al., 2014). Other parents report concerns about chemicals in vaccines and possible unforeseen future effects of vaccination (Martin & Petrie, 2017). Yet longitudinal research has suggested no negative long-term effects of vaccines administered in infancy (Henry et al., 2018; Su et al., 2017; Wessel, 2017).

      A challenge to immunizing children is that the vaccination schedule is complicated, with specific vaccines administered at specific times in development (Kurosky, Davis, & Krishnarajah, 2017). Even when children receive the full schedule of vaccinations, many do not receive them on the timetable recommended by the National Vaccine Advisory Committee. Vaccine timeliness is important because the efficacy of early and late vaccination is not always known and may vary by disease. When a child receives a vaccination may be just as important as whether the child receives it in promoting disease resistance.

      What Do You Think?

      What do you think are the most compelling reasons parents might choose not to vaccinate their children? How might you counter these reasons? ●

      Interventions to increase vaccination rates tend to focus on education and counseling and improving access to vaccines (Ventola, 2016). Health care workers can inform parents about vaccination by describing the infections that they prevent, discussing the research supporting their use, and dispelling myths. Offering combination vaccines that include several at once minimizes the number of injections and visits. Providing opportunities to administer vaccinations during all pediatric visits—well, sick, and follow-up—as well as by nurses can increase compliance. At the community level, advertising, public messaging campaigns, and social media and text messaging educational materials and reminders can inform parents of the benefits of vaccinations. Access to free vaccines and opportunities for vaccination within the community, such as at day care facilities, walk-in clinics, pharmacies, and financial aid offices, can help remove financial barriers to vaccination.

      Thinking in Context 4.1

      1 Identify ways in which contextual factors influence growth. What do parents need to know about these factors? How might you increase parents’ knowledge?

      2 Prepare a brief presentation for parents of newborns explaining SIDS, risk factors for it, and what parents can do to help protect their infants.

      Brain Development During Infancy and Toddlerhood

      Infants’ bodies grow rapidly, but the most dramatic changes during infancy are much less visible. All of the developments in infants’ physical and mental capacities are influenced by the changes that occur in the brain. At birth, the brain is about 25% of its adult weight, and it grows rapidly throughout infancy, reaching about 70% of its adult weight by 2 years of age (Lyall et al., 2015). As the brain develops, it becomes larger and more complex.

      The Neuron

      The brain is made up of billions of cells called neurons. Neurons are specialized to communicate with one another to make it possible for people to sense the world, think, move their bodies, and carry out their lives. As shown in Figure 4.6, neurons have distinct structures that set them apart from other cells and enable the communicative functions characteristic of neurons. Dendrites are branching receptors that receive chemical messages (called neurotransmitters) from other neurons that are translated into an electrical signal (Stiles, 2017). The axon is a long tube-like structure that extends from the neuron and carries electrical signals to other neurons. Neurons do not touch. Instead, there are gaps between neurons called synapses. Once the electrical signal reaches the end of the axon, it triggers the release of the neurotransmitter, which crosses the synapse to communicate with the dendrites of another neuron (Carson, 2014). This process of neural transmission is how neurons communicate with other neurons. Neurons also communicate with sensory and motor cells. Some axons synapse with muscle cells and are responsible for movement. The dendrites of some neurons synapse with sensory cells, such as those in the eyes or ears, to transfer sensory information such as vision and hearing (Gibb & Kovalchuk, 2018). Finally, axons are often coated with a fatty substance called myelin, which speeds the transmission of electrical impulses and neurological function.

      Description

      Figure 4.6 The Neuron

      Processes of Neural Development

      The first neurons form early in prenatal development, in the embryo’s neural tube, through a process called neurogenesis. We are born with more than 100 billion neurons, more than we will ever need—and more than we will ever have at any other time in our lives. Some of our neurons die, but neurogenesis continues throughout life and new neurons are formed, although at a much slower pace than during prenatal development (Stiles et al., 2015). As the brain develops, new neurons migrate along a network of glial cells, a second type of brain cell that outnumbers neurons (Gibb & Kovalchuk, 2018). Glial cells nourish neurons and move throughout the brain to provide a physical structure to the brain. As shown in Figure 4.7, neurons travel along glial cells to the location of the brain where they will function, often the outer layer of the brain, known as the cortex, and glial cells instruct neurons to form connections with other neurons (Kolb, Whishaw, & Teskey, 2016).

      Description

      Figure 4.7 Glial Cell–Neuron Relationship

      Neurons migrate along thin strands of glial cells

      Source: Gasser and Hatten (1990).

      At birth, the networks of neurons are simple, with few connections, or synapses, between neurons (Kolb et al., 2016). Early in infancy, major growth takes place. Neurons and glial cells enlarge. The dendrites grow and branch out, increasing synapses with other neurons, a process called synaptogenesis. Synaptogenesis peaks in different brain regions at different ages (Remer et al., 2017). The most active areas of synaptogenesis during the first 5 weeks of life are in the sensorimotor cortex and subcortical parts of the brain, which are responsible for respiration and other essential survival processes. The visual cortex develops very rapidly between 3 and 4 months and reaches peak density by 12 months of age. The prefrontal cortex—responsible for planning and higher thinking—develops more slowly and is not complete until early adulthood (Tamnes et al., 2017).

      In response