The muscular tone is the condition of permanent semicontraction (slight constraction) which the muscle always has during the resting state. The muscular tone can be observed in a healthy person (without neurological problems) both in the striated and smooth muscles. It is a nervous system reflex phenomenom called "myotatic reflex". The muscular tone reflex varies in intensity according to the central nervous system nervous mechanism of regulation, being the origin of other reflexes called "tonic", such as the posture reflex, which is very necessary for the maintenance of a any given body position in space; it is the postural tone, through which we are able to maintain an erect body position.
Since the striated muscle's muscular tone is a reflex activity, its nervous centers are located in the spinal cord. Thus, it can be terminated if the spinal cord is destroyed, or if the efferent, motor, nervous fiber that innervate the muscle is severed. However, the muscular tone can also be ended if the afferent fibers is cut, even when the efferent fiber is intact.
The centers of the smooth muscle's muscular tone of blood vessels is situated in the medulla oblongata vasomotor centers and is effectuated through vasoconstrictor, sympathetic nerve fibers.