A type of tremor not mentioned by others results
from damage to the cerebellum.
The tremor of Parkinson’s is called “resting”
because it may not be as noticeable on “intention” that is, when one performs a
voluntary motor behaviour,
A cerebellar tremor, on the other hand, is absent
at rest. However, it is noticed on intention, when one tries to perform a motor
act, such as putting a straw into the mouth. The closer one gets to the mouth,
the greater the tremor.
This is because the cerebellum normally acts as a
“steering wheel”. It does not initiate the movement, but once it is in
progress, the cerebellum acts to fine tune it.
Using the analogy of a car, the gas pedal (motor
system) initiates the behaviour. The cerebellum is the steering wheel that
guides it. The brakes are the basal ganglia, which enable complete stopping. In
Parkinson’s, (disease of the basal ganglia) the brakes don’t fully engage, so
the person is left with ongoing motion (resting tremor).
It is fairly normal for people to tremble in
response to excess sympathetic nervous system activation (to “shake like a
leaf” due to fear)
Reference: Joyce Schenkein
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