The Autonomic Nervous System
An important functional division of the nervous system is the Autonomic Nervous System (ANS).
The Autonomic Nervous System consists of a separate group of afferent and efferent neurons that control the automatic, or visceral, functions of the body ‘those over which we do not exercise conscious control’ such as blood pressure, digestion, blood circulation, and respiratory activity.
The ANS becomes active when afferent signals from part of the body send impulses to the center of the spinal cord, brain stem, or hypothalamus (a small area of the brain that connects to most nervous system regions and exerts overall control over internal functions.) These centers, in turn, transmit the appropriate reflex responses back to the visceral organs to control their activities.
Sympathetic and Parasympathetic Nervous System: Two Major Divisions of Autonomic Nervous System
There are two major divisions of the Autonomic Nervous System through which the body transmits all autonomic impulses:
- The sympathetic nervous system (SNS) which originates in the thoracic and lumbar areas of the spinal cord;
- The parasympathetic nervous system (PSNS), which originates in the brain stem and sacral area of the spinal cord.
The actions of these two systems oppose and balance each other.
The American Autonomic Society (AAS) is a medical association made up of autonomic specialists.