Naming muscles according

to their action

Sanjaya Adikari

Department of Anatomy

Faculty of Medicine

Peradeniya

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

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

Prime mover & antagonist…

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

Synergists…

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

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

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

Fixators…

• Eg:- Abduction of the little finger

– Abductor digiti minimi is the prime mover

– Flexor carpi ulnaris acts as a fixator of pisiform bone