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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