Extrinsic muscles
- Long flexors and extensors that originate in the forearm and insert on the digits and thumb
- Provide the power of the grip
- Include: flexor digitorum superficialis (FDS), flexor digitorum profundus (FDP), extensor digitorum communis (EDC)
Intrinsic muscles
- Small muscles that originate and insert within the hand
- Modify the actions of the extrinsic muscles to produce finer skilled movements
- Thenar eminence
- Abductor pollicis brevis
- Flexor pollicis brevis
- Opponens pollicis
- NB: The two muscles of the thumb that are affected in carpal tunnel syndrome are the abductor pollicis brevis and the opponens pollicis
- Hypothenar eminence
- Abductor digiti minimi
- Flexor digiti minimi
- Opponens digiti minimi
- Lumbricals
- Interosseus muscles
- 4 dorsal
- 3 palmar
- NB: lumbricals and interosseus muscles are numbered from lateral to medial
Opponens pollicis is deep to abductor pollicis brevis. Opponens Digiti Minimi is deep to abductor digiti minimi.
Image Source: Anatomy and Cell Biology, Queen's University
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