The commonest type of spinner - the off-break and orthodox left arm spinners (like Monty Panesar and Graeme Swann) should properly be caused forearm spinners
, since it is the supination
of the forearm which imparts spin to the ball.
Supination is the rotation of the forearm from a position with the palm facing down and the thumb on the medial (middle) side being rotated to the palm is upwards and the thumb is on the lateral (out) side.
It is this rotation of the forearm which generates spin - and it has almost nothing to do with the fingers (they merely grip the ball firmly) - so the name 'finger spinner' is wrong and misleading.
True finger spinners are those rare types who use a finger flick to impart spin - such as Mendis or Herath's carrom ball, or from the past Jack Iverson.
Wrist spinners are mostly leg break and chinaman bowlers, who bowl with the forearm in pronation (thumb medially rotated - but Saeed Ajmal is a new kind of wrist spinner
who bowls with the forearm in supination (thumb laterally rotated).
What of Murali?
He was mostly a shoulder
spinner. The whole of his arm rotated, and the ball was either an off-break or a doora according to whether the wrist was flexed/ folded palm towards arm (doosra) or extended/ with wrist 'cocked' and back of hand towards arm (off break).
Some googlies are also shoulder-spun - bowled mostly from shoulder rotation, especially when the bowler has a round arm action like Shane Warne.
Warne's most serious injury was of his shoulder, and resulted from bowling a sequence of practice googlies to Ian Healy.
(By contrast, right arm wrist spinners with a high or vertical arm action - such as Chandrasekar or Kumble - tend to bowl googlies (or top-spinners) as their stock delivery rather than leg breaks; and their googly is bowled with a flick of the wrist and not by rotating the whole arm from the shoulder.)