Why do we sometimes move without meaning to?
The nerve impulses that make skeletal muscles move are under conscious control, most of the time. Losing that control can be harmless, such as shivering in the cold, or more serious, as a result of diseases that affect the nervous system. A well-known example is Parkinson’s disease, in which cells that make the neurotransmitter dopamine gradually disappear from one brain region, the substantia nigra.
Early symptoms of Parkinson’s disease include too much movement (shaking) and too little (freezing or rigidity). In cases of another disease called Tourette’s syndrome, movement is normal most of the time, but people with this complex condition sometimes have involuntary, repetitive tics, often involving the facial muscles or shoulders.Lead image:
Sean MacEntee/Flickr CC BY