Chapter 5

Chapter 5
Body, Brain, and Health
The Endocrine System
 the body’s “slow”
 a set of glands that
secrete hormones
into the
Hormonal Influences on Growth and
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
– 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
• 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
Emotional Content of
Brain Lateralization
Our Divided Brain
Corpus callosum
 large band of
neural fibers
 connects the
two brain
Brain Development
• Never truly complete
– Changes occur across lifespan
• Growth spurts in infancy, childhood and
• 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
• 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