The human nervous system is a control system which regulates the body's responses to internal and external stimuli.
Nerve cells called neurons are the conducting units of the human nervous system.
The human nervous system is the most rapid and precise of all the control systems in the body.
The autonomic nervous system is that part of the nervous system concerned with commands for smooth muscle tissue, cardiac muscle tissue and glands.
It is organised into two major subdivisions:
the sympathetic nervous system
the parasympathetic nervous system