Why is my index finger involuntarily having spasams?

Fasciculations...: Are usually harmless twitches which can occur in any skeletal muscle in the body. There are several pathological conditions associated with these spasms which are usually accompanied by abnormalities on neurological examination and/or on a special test called electromyogram (emg). See a doctor if your symptoms are bothersome or are of concern to you.

Muscle/tendon/nerve?: This could be due to one of several conditions including electrolyte abnormalities but is likely a benign process such as muscle fatigue. However other causes should be evaluated and excluded. See your physician.