Chapter 5 Body, Brain, and Health The Endocrine System the body’s “slow” chemical communication system a set of glands that secrete hormones into the bloodstream Hormonal Influences on Growth and Development Neural Communication The Brain and Nervous System • Neurons – Dendrite, cell body, and axon Principles of Growth • Cephalocaudal principle • • – Growth occurs in a head-to-tail direction Proximodistal principle – Growth and development of muscles from the center outward to the extremities Orthogenetic principle – Development starts globally and undifferentiated – Moves toward increasing differentiation and hierarchical integration The Infant • Synaptogenesis • • – Growth of synapses, during childhood Synaptic pruning – Removal of unnecessary synapses Developing brain has plasticity – Responsive to the individual’s experiences and can develop in a variety of ways Figure 5-2 Plasticity • Responsiveness to experiences – Can be negative • Vulnerable to damage • Environmental deprivation – Can be positive • Aids in recovery from from injury • Can compensate for each other • Can benefit from stimulation • Allows for adaptability Visual-spatial Emotional Content of Language Brain Lateralization Our Divided Brain Corpus callosum large band of neural fibers connects the two brain hemispheres Brain Development • Never truly complete – Changes occur across lifespan • Growth spurts in infancy, childhood and adolescence • Full adult weight by about age 16 • Processing speed increases in adolescence • Myelination continues into adulthood The Changing Brain • Brain development is never truly complete • Neurogenesis • – Process of generating new neurons Elderly adults may end up with 5–30% fewer neurons than early adulthood – Neuron loss greater in areas that control sensory and motor activities • Increased activity in the prefrontal cortex Brain Development The Aging Brain – Gradual and mild degeneration Elderly adults – 5-30% fewer neurons than younger adult – Greater loss in sensory-motor areas – Plasticity still possible Main result of age is slower processing • Programmed theories of aging – Maximum life span (species specific) – Hayflick Limit – cells from embryos divide a limited amount 50 ± 10; for adult cells even less telomeres • Random error theories of aging – Free radicals – toxic by-products of the metabolism of O2 damage cells and their functioning (also damage DNA) • Interaction of the two – or more