In the clonic variety there are undue rapidity and increased frequency of the movements.
In the tonic variety, the duration of the contraction is prolonged.
The intensity of the movements, likewise, is abnormal in degree.
In spite of these disfigurations, so to speak, of the original movement, it is practically always possible to detect in them co-ordination and purpose, the cause and the significance of which ought to become the object of our search.
The motor disorder can never be reduced to mere fibrillation, nor indeed to fascicular contraction unless in some one muscle different bundles have different physiological attributes. It is usual for several muscles to be concerned, and their anatomical nerve supply may be from separate sources.
Like ordinary functional motor acts, tics are distinguished by co-ordination of muscular contraction and repetition; they are preceded by a desire for their execution, and succeeded by a feeling of satisfaction.
These features, however, are carried to excess.
In addition, the functional act is inapposite, sometimes even harmful; it may be described as a parasite function.
The muscular contractions follow each other at irregular intervals; they come in attacks, which, it is true, are highly variable in frequency, duration, and degree.
Volition and attention exercise a restraining influence on the motor phenomena, but repression is accompanied by malaise, sometimes by actual anguish.