Naming muscles according to their action

1. Naming muscles according to their action Sanjaya Adikari Department of Anatomy Faculty of Medicine Peradeniya

2. Origin and insertion • Origin – Proximal attachment where there is less movement • Insertion – Distal attachment where there is greater movement • Use the terms, proximal/ distal attachment to avoid confusions

3. Prime mover & antagonist • Prime mover is the muscle that does the desired movement at a joint • Antagonist is the muscle that has the action opposite to that of prime mover • Eg:- Flexion of the elbow joint • Biceps brachii is a prime mover • Triceps is the antagonist

4. Prime mover & antagonist…

5. Synergist • Synergist assists the prime mover by preventing unwanted movements at other joints • Eg:- Flexion of the fingers • Flexor digitorum profundus and superficialis are the prime movers • Extensor muscles of the wrist joint are the synergists

6. Synergists…

7. Synergists… • Eg:- Supination of the pronated forearm • Biceps brachii and spinator are the prime movers • Triceps acts as a synergists of biceps to prevent flexion of the elbow joint

8. Synergists… • Eg:- Flexion of the elbow joint • Biceps brachii is a prime mover • Posterior fibres of deltoid acts as a synergist to prevent extension of the shoulder joint

9. Fixators • Fixators stabilize one attachment of a muscle so that the contraction moves the other end • Eg:- Abduction of the shoulder joint • Deltoid is the prime mover • Levator scapulae, rhomboids and trapezius are fixators

10. Fixators… • Eg:- Abduction of the little finger • Abductor digiti minimi is the prime mover • Flexor carpi ulnaris acts as a fixator of pisiform bone