The receptive organs of the muscular sense and of the semicircular canals are to be regarded as the sites of origin of this reflex tonus of the skeletal muscles.
Striped muscles possessing an autochthonous tonus appear to be the various sphincter muscles.
There slowly successive phases of increased and of diminished tonus regularly alternate, and upon them are superposed the rhythmic "beats" of the pulsating heart.
This gentle continuous activity of the neuron is called its tonus.
In tracing the tonus of neurons to a source, one is always led link by link against the current of nerve force - so to say, "up stream" - to the first beginnings of the chain of neurons in the sensifacient surfaces of the body.