The fingers are controlled by a complex network of intrinsic and extrinsic muscles located in the hand and forearm.
These muscles can be categorized as follows:
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Extrinsic Muscles: These muscles originate in the forearm and have long tendons that extend into the hand to control finger movement. They are responsible for powerful gripping and gross motor movements.
- Flexor Digitorum Profundus: Flexes the DIP (distal interphalangeal) joints of the fingers.
- Flexor Digitorum Superficialis: Flexes the PIP (proximal interphalangeal) joints of the fingers.
- Extensor Digitorum: Extends the MCP (metacarpophalangeal) joints and PIP/DIP joints of the fingers.
- Extensor Indicis: Extends the index finger and assists in wrist extension.
- Extensor Digiti Minimi: Extends the little finger and assists in wrist extension.
- Flexor Pollicis Longus: Flexes the thumb.
- Extensor Pollicis Longus: Extends the thumb.
- Extensor Pollicis Brevis: Extends the thumb.
- Abductor Pollicis Longus: Abducts the thumb.
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Intrinsic Muscles: These muscles are located within the hand itself and are responsible for fine motor movements and intricate finger control.
- Dorsal Interossei: Abduct (spread) the fingers away from the midline of the hand. There are four dorsal interossei. They also flex the MCP joints.
- Palmar Interossei: Adduct (bring together) the fingers toward the midline of the hand. There are three palmar interossei. They also flex the MCP joints.
- Lumbricals: Flex the MCP joints and extend the PIP and DIP joints.
- Thenar Muscles (thumb): Control thumb movements (flexion, abduction, opposition). Examples include the abductor pollicis brevis, flexor pollicis brevis, opponens pollicis, and adductor pollicis.
- Hypothenar Muscles (little finger): Control little finger movements (flexion, abduction, opposition). Examples include the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi.
In summary, both extrinsic and intrinsic muscles work in coordination to allow for a wide range of finger movements, from powerful grasping to delicate manipulations. The extrinsic muscles provide the power, while the intrinsic muscles fine-tune the movements.
