HI....IF YOU KNOW THE ORIGIN AND INSERTIONS OF THE MUSCLES YOU CAN DETERMINE THEIR ACTIONS. THE MUSCLE ALWAYS MOVES TOWARD THE ORIGIN TO SHORTEN THE ANGLE. IF THE MUSCLE CROSSES 2 JOINTS IT WILL MOVE THE DISTAL PART, USUALLY ASSIST FLEXION,ADDUCT OR ABDUCT, AND THE MAIN ACTION WILL BE ON THE MORE PROXIMAL JOINT.
AS FOR THE UPPER LIMB, ALL OF THE WRIST EXTENSORS ORIGINATE ON THE LATERAL EPICONDYLE OF THE HUMERUS, LOOK AT THEIR NAMES THEY WILL ALL EXTEND THE WRIST AND IF THE NAME HAS ANYTHING ELSE SUCH AS DIGITORUM IT WILL MOVE THE FINGERS TOO, IF IT SAYS CARPI IT WILL EXTEND THAT AREA BUT EITHER ADDUCT FOR ULNARIS OR ABDUCT FOR RADIUS,AND THE FLEXORS ON THE MEDIAL EPICONDYLE.
FOR THE ROTATOR CUFF MUSCLES: SITS,SUPRASPINATUS, INFRASPINATUS, TERES MINOR AND SUBSCAPULARIS
ALL OF THEIR ORIGINS ARE IN THE FOSSA OF THEIR RESPECTIVE NAMES, OTHER THAN TERES MINOR AND THEY ALL INSERT ON THE GREATER TUBERCLE OF THE HUMERUS EXCEPT SUBSCAPULARIS, LESSER TUBERCLE.SITS: THE FIRST ABDUCTS, SECOND TWO LATERALLY ROTATE AND THE LAST MEDIALLY ROTATES.I HOPE SOME OF THIS HELPS
