Our nervous system plays a vital role in how we think, feel, and act. Neurons, the basic building
blocks of the body’s circuitry, receive signals through their branching dendrites and cell bodies
and transmit electrical impulses down their axons. Chemical messengers called
neurotransmitters traverse the tiny synaptic gap between neurons and pass on excitatory or
The central nervous system consists of the brain and spinal cord. The peripheral nervous
system consists of the somatic nervous system, which directs voluntary movements and
reflexes, and the autonomic nervous system, which controls the glands and muscles of our
Evolution has elaborated new brain systems on top of old. Within the brainstem are the
oldest regions, the medulla and the reticular formation. The thalamus sits atop the brainstem and
the cerebellum extends from the rear. The limbic system includes the amygdala, the
hippocampus, and the hypothalamus. The cerebral cortex, representing the highest level of brain
development, is responsible for our most complex functions.
Each hemisphere of the cerebral cortex has four geographical areas: the frontal, parietal,
occipital, and temporal lobes. Although small, well-defined regions within these lobes control
muscle movement and receive information from the body senses, most of the cortex—its
association areas—are free to process other information. Experiments on split-brain patients
suggest that, for most people, the left hemisphere is the more verbal and the right hemisphere
excels in visual perception and the recognition of emotion. Studies of people with intact brains
indicate that each hemisphere makes unique contributions to the integrated functions of the
Hormones released by endocrine glands affect other tissues, including the brain. The most
influential endocrine gland, the pituitary gland, releases hormones that influence growth, and its
secretions also influence the release of hormones by other glands. The nervous system directs
endocrine secretions, which then affect the nervous system.
Why psychologists are concerned with human biology.
Everything psychological is simultaneously biological. We think, feel, and act with our bodies. By
studying the links between biology and psychology, biological psychologists are gaining new
clues to sleep and dreams, depression and schizophrenia, hunger and sex, stress and disease.
The structure of a neuron; How neural impulses are generated.
A neuron consists of a cell body and branching fibers: The dendrites
receive information from
sensory receptors or other neurons, and the axons
pass that information along to other neurons.
A layer of fatty tissue, called the myelin sheath, insulates the fibers of some neurons and helps