Voluntary and involuntary movements: A proposal from a clinician

In this communication, I first summarize the mechanisms underlying human voluntary movements and define the involuntary movements (medical term).

Human movements are classified into two main kinds: intentional movements and non-intentional movements in which the involuntary movements are included. Non-intentional movements have many kinds of movement: normal non-intentional movements (associate movements, mirror movements or juggling knees etc.), several reflexes (spinal tendon, spinal flexion, spino-bulbo-spinal, cortical reflexes and startle response) and pathological non-intentional movements which should be treated (so called "involuntary movements" in clinical practice, medical term of involuntary movement).

The final motor commands for movements are mediated by several descending motor pathways. These final pathways are modified, regulated by two main loops (basal ganglia loop and cerebellar loop).

The involuntary movements are produced by a non-intentional, pathological activation anywhere within the final common pathways or the above two loops. I would like to personally divide those into four major groups.

Some oscillation mechanisms may produce tremor: one site oscillation or loop oscillation.

Sudden, brief, shock-like involuntary movements arising from anywhere from the cortex to the muscle.

Suddenly appearing, irregular, phasic movements which are usually mimicked by normal subjects.

Sustained, long duration muscle contraction sometimes associated with torsion components.