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Chapter 7 Summary & Outline

Growth and Development of the Brain Are Orderly Processes

In the human embryo, the brain develops from a neural tube with three subdivisions that will become the forebrain, midbrain, and hindbrain. Review Figure 7.1, Web Activities 7.1, 7.2, and 7.3

Study questions: 1 | 2 | 3 | 4 | 5 | 6

Early embryological events in the formation of the nervous system include a sequence of six cellular processes: (1) neurogenesis, (2) cell migration, (3) cell differentiation, (4) synaptogenesis, (5) neuronal cell death, and (6) synapse rearrangement. Review Figure 7.2, Web Activities 7.4, 7.5, and 7.6
In simple animals such as the nematode Caenorhabditis elegans, neural pathways and synapses form according to an innate, genetic plan that specifies the precise relations between growing axons and particular target cells. In more-complicated animals—including all vertebrates—cell-cell interactions determine the fate of individual neurons and glia. Review Figure 7.4 and Table 7.1, Web Activities 7.7 and 7.8
Although in humans most neurons are present at birth, most synapses develop after birth and continue developing into adulthood. Review Figure 7.9

Study questions: 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36

Fetal and postnatal changes in the brain include the myelination of axons by glial cells and the development of dendrites and synapses by neurons. Review Figure 7.15

Study questions: 37 | 38 | 39

Among the many determinants of brain development are (1) intrinsic genetic information and (2) a multitude of extrinsic factors, such as neurotrophic factors, nutrition, and experience. These factors interact extensively because extrinsic factors like experience can affect gene expression.
Impairments of fetal development that lead to intellectual disability can be caused by the use of drugs such as alcohol during pregnancy. Review Figure 7.16
Maldevelopment of the brain can occur as a result of mutations or other genetically controlled disorders. Some, such as Down syndrome and fragile X syndrome, are related to disorders of chromosomes; others are metabolic disorders, such as phenylketonuria (PKU)). Review Figure 7.18
Gene expression is affected by environmental factors and experience, so epigenetic influences can profoundly affect brain development without altering the sequence of nucleotides in any genes. Similarly, genetically identical individuals, either twins or clones, do not display identical behaviors. Review Figure 7.19

Study questions: 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55

Experience affects the growth and development of the nervous system. Experience can induce and modulate the formation of synapses, maintain synapses that are already formed, or determine which neurons and synapses will survive and which will be eliminated. Review Figures 7.20–7.22

Study questions: 56 | 57 | 58

Attention deficit hyperactivity disorder (ADHD), which is characterized by distractibility, hyperactivity, and impulsiveness—exaggerations of traits common in childhood—is correlated with abnormalities in the prefrontal cortex and cerebellum, as well as in brain activity.
Autism appears to be a disruption in the development of cognitive processing about social interactions, which impairs the development of language and other behaviors. Review Figure 7.24

Study questions: 59 | 60 | 61

The brain continues to change throughout life. Old age is accompanied by the loss of neurons and synaptic connections in some regions of the brain. In some people the changes are more severe than in others; pathological changes characterize the condition of early-onset senile dementia known as Alzheimer’s disease. Review Figure 7.25
Alzheimer’s seems to be caused by a buildup of β-amyloid, causing degenerative extracellular senile plaques and intracellular neurofibrillary tangles through much of the cortex. Several genes, including those that encode the enzymes presenilin and apolipoprotein E (ApoE), influence the rate of amyloid accumulation and therefore the risk of Alzheimer’s. Mental activity, physical activity, and adequate sleep seem to postpone the onset of Alzheimer’s. Review Figures 7.26–7.28

Study questions: 62 | 63 | 64 | 65 | 66 | 67 | 68

The brain and behavior develop on two very different but equally essential timescales: eons of evolution versus days and years of individual development.

Study questions: 69