Why does the human hand tremble?

Answer 1

Factors that can make a normal tremor more noticeable include stress, anxiety, fatigue, withdrawal of alcohol or certain other drugs (such as opioids), an overactive thyroid gland (hyperthyroidism), consumption of caffeine, and use of certain drugs. The reason for all trembling ultimately is due to way muscles work. At a microlevel there are [[sarcomeres]], which are the base unit of muscles, and are analagous to the thinnest threads of a muscle. These threads actually consist of to parts that overlap by a greater of lesser extent depending on whether the muscles are expanding or contracting. At any given time half the sarcomeres are at rest, and the other half take up the tension if the muscle is in use, and alternate taking up the strain. When the body is stressed (eg due to fatigue, stress, other factors), then this mechanism does not work perfectly and the result is that when the alternate groups of sacromeres do not perfectly take the strain the muscle will tremble. This is particularly noticeable at the extremities as it is easier for a small motion to be exagerrated.

Further links: http://www.YouTube.com/watch?v=U2TSaz8-yNQ http://www.maxanim.com/physiology/Sarcomere/Sarcomere.htm http://en.wikipedia.org/wiki/Sarcomere