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The central nervous system (CNS) can be likened to a computer processor that is the command center for the functions of the body. The peripheral nervous system is like a set of cables that transfers critical data from the CNS to the body and then feeds back information from the body to the CNS. This sophisticated “computer system” continually makes appropriate adjustments to its inputs and outputs to allow us to react and adapt to changes in the external and internal environments (sensory systems), to maintain posture, permit locomotion, and use the fine motor control in our hands to create pieces of art (somatomotor system), to maintain homeostasis (autonomic nervous system), to regulate the transitions between sleep and wakefulness (consciousness), and to allow us to recall past events and to communicate with the outside world (higher cortical functions). This section on neurophysiology will describe the fundamental properties and integrative capabilities of neural systems that allow for the exquisite control of this vast array of physiologic functions. Medical fields such as neurology, neurosurgery, and clinical psychology build on the foundation of neurophysiology.

There are over 600 known neurologic disorders. Nearly 50 million people in the United States and a 1 billion people worldwide have experienced damage to the central or peripheral nervous system. Each year, nearly 7 million people die of a neurologic disorder or its complications. Neurologic disorders include genetic disorders (eg, Huntington disease), demyelinating diseases (eg, multiple sclerosis), developmental disorders (eg, cerebral palsy), degenerative diseases (eg, Parkinson disease and Alzheimer disease), an imbalance of neurotransmitters (eg, depression, anxiety, and eating disorders), trauma (eg, spinal cord and head injury), and convulsive disorders (eg, epilepsy). There are also neurologic complications associated with cerebrovascular problems (eg, stroke) and exposure to neurotoxic chemicals (eg, nerve gases, mushroom poisoning, and pesticides).

Advances in stem cell biology and brain imaging techniques, a greater understanding of the basis for synaptic plasticity of the brain, a wealth of new knowledge about the regulation of receptors and the release of neurotransmitters, and the detection of genetic and molecular defects that lead to neurologic problems have advanced our understanding of the pathophysiologic basis for neurologic disorders. They have also led to better therapies to prevent or reverse the physiologic deficits resulting from neurologic disorders.

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