The autonomic nervous system, also known as the visceral motor system, is the portion of the nervous system that regulates and controls the glands, muscles and organs throughout the body. As the name implies, the autonomic nervous system is autonomic, carrying out functions without conscious thought. The autonomic nervous system is responsible for the rhythm of the heart, operation of the sweat glands, involuntary muscle movements, and much more.
Stimulation of the autonomic nervous system results in visceral reflexes; the unconscious, involuntary reactions to stimuli. This stimulation follows the typical chain of nerve signalling, beginning at the nerve receptors, signalling neurons to travel toward and then away from the central nervous system, finally ending their journey at the effectors, which carry out the reflex or reaction.
Divisions of the autonomic nervous system
The autonomic nervous system, much like the nervous system as a whole, can be separated out into unique and separate subdivisions. The autonomic nervous system is typically divided into two subdivisions; the sympathetic division and the parasympathetic division.
The sympathetic division is responsible for keeping the body alert and aware and is greatly involved in the “fight or flight” instincts. The sympathetic division of the autonomic nervous system is also responsible for more subtle changes, such as increased heart rate, faster breathing and increased blood pressure. An example of the sympathetic division of the autonomic nervous system at its most extreme is the “fight or flight” instinct. The senses are heightened, heartrate and breathing speed, and excretory function are inhibited.
The parasympathetic division of the autonomic nervous system is generally regarded as having an opposite, calming, affect as the sympathetic division of the autonomic nervous system. The parasympathetic division of the autonomic nervous system regulates the calmer functions (such as digestion and elimination) of the body, such as those occurring during times of rest.
Both the sympathetic and parasympathetic division of the autonomic nervous system are functioning together at any given time, however, depending on stimuli from the environment, one may be acting dominantly. The balance or imbalance of the two divisions is referred to as autonomic tone. When the parasympathetic division is dominant, the autonomic nervous system has a parasympathetic tone. The opposite is true of sympathetic tone.
More on the nervous system
Subdivisions of the Nervous System
The Structure and Function of Neurons in the Nervous System
Understanding Nervous Tissue