By exchanging signals, the cortex on the basal ganglia allow your hand muscles to hold their position. This cycle of signals repeats continuously entire time your hand is extended, but by most mysteries of brain, this one involving motor control is not fully understood by scientists. However, scientists believe that the mental effort required to hold your hand still causes the muscles in your hand to contract a bit at a regular a* and therefore, experiences a tremor, even under normal circumstances. When you are nervous, the part of your brain that regulates anxiety interferes with response cycle between the cortex and basal ganglia, increasing the severity of these muscle contractions and then altering your ability to actually control the position of your hand. Though your hand will shake a little bit under normal conditions, it will shake a lot more when these nervous feelings influence your hand control.

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