Fasciculation

A fasciculation, or "muscle twitch", is a small, local, involuntary muscle contraction and relaxation. At times it may be visible under the skin. Deeper areas can be detected by EMG testing. A fasciculation can happen in any skeletal muscle in the body. Fasciculations can occur in normal healthy people.Sabyasachi Sircar, Principles of Medical Physiology (Stuttgart; New York: Thieme, 2008), p. 116 One uncommon reason for them is due to a lower motor neuron lesion that may be caused by any of several diseases. One example would be Amyotrophic Lateral Sclerosis.

 References 

 Other websites 
What is a Fasciculation? About.com 

Category:Symptoms
Category:Muscular system