The muscles of the thumb are primarily located in the thenar eminence, with additional contributions from muscles in the forearm and hand. These muscles work together to allow for a wide range of movements, including flexion, extension, abduction, adduction, opposition, and circumduction.
Muscles of the Thumb:
These muscles can be categorized by their location and function:
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Thenar Muscles (Intrinsic): These muscles are located at the base of the thumb and form the thenar eminence. They are crucial for fine motor control and opposition (bringing the thumb across the palm to touch the fingers).
- Abductor Pollicis Brevis: Abducts the thumb (moves it away from the palm).
- Flexor Pollicis Brevis: Flexes the thumb (bends it towards the palm).
- Opponens Pollicis: Opposes the thumb (rotates it to face the fingers).
- (Adductor Pollicis is sometimes considered a thenar muscle, but it has a different nerve supply and is located deeper.)
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Extrinsic Thumb Muscles (Located in the Forearm): These muscles have long tendons that extend into the thumb and control its movements from the forearm.
- Flexor Pollicis Longus: Flexes the distal phalanx (tip) of the thumb.
- Extensor Pollicis Longus: Extends the distal phalanx of the thumb and also abducts the wrist.
- Extensor Pollicis Brevis: Extends the metacarpophalangeal joint of the thumb (the joint at the base of the thumb).
- Abductor Pollicis Longus: Abducts the thumb and assists in wrist abduction.
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Other Muscles Contributing to Thumb Movement:
- Adductor Pollicis: Adducts the thumb (moves it towards the palm). This muscle has two heads (oblique and transverse). While not part of the Thenar eminence, it's crucial for thumb function.
- Interossei and Lumbricals: While their primary action isn't thumb movement, they contribute to stabilization and fine motor control in conjunction with the other thumb muscles.
In summary, the muscles responsible for thumb movement and function include the thenar muscles (abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis), the extrinsic muscles originating in the forearm (flexor pollicis longus, extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus) and the adductor pollicis. Also, interossei and lumbricals are important to maintain thumb function.
