Yup... dystonia is caused by damage to the basal ganglia - the gray stuff. Myoclonus can be caused by damage to the cortex, or damage to the spine.
I have myoclonus and spasticity. Spasticity is 'unwanted muscle tone.' Essentially as nerves get damaged, they aren't making a perfect connection with the muscle. When the muscle isn't getting its constant signal from the brain to stay relaxed, it contracts. So spastic muscles are staying just a little contracted,. and the spasticity can turn into a spasm - total contraction of the muscle.
Myoclonus seems to be involuntary jerks of the body. Sometimes they can make your body tense up, and sometimes it's just a movement. I get both! The tense-making ones happen in the mornings, when I start to get up. My legs will completely tense up and try to bend, and usually I end up pulling my feet up as well. The involuntary jerks can start up about mid-morning, and keep going for a few hours. Usually I'm so tired that I call in sick and go to bed, and after I've woken up, they've gone away.
My understanding is myoclonus is more the intermittent jerks and twitches. Dystonia is a neurological movement disorder, in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures. Dystonia is more of a continuous vs, intermittent condition.
Bob